From: Robert L Barns <75612.2635@..............> Subject: Geophones Date: Mon, 30 Jun 1997 20:19:59 -0400 Hi gang, I just got the current catalog of Mitcham Industries (www.mitchamindustries.com). Among the large list of wild and wonderful= seismic equipment (some around $500,000) is "3 Hz l15B single phone w/Muller clip". They have 50 for $25 ea. (This is more like my price range.) They have a bunch more with higher freq. cut-offs. I know nothing about these things but will buy one to play with. Two questions:1. What is a Muller clip? and 2. Where can I get pin-outs etc= =2E so that I can hook it up. I think that someone on this list stated that these things are vertical= s unless otherwise labeled. Bob Barns _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: David A Nelson Subject: Re: Geophones Date: Tue, 01 Jul 1997 12:31:27 +1200 Bob I spoke to the CEO of Mitchum two weeks ago and unfortunately the L15B's are sold out and will not be replaced because Mark products who supplied them no longer make that model. The Muller clip is just a small forcefit clip that slides onto the two contact prongs of the seismometer there are only to pins on the seismometer and they just go straight to the input of your preamp Dave N. At 08:19 PM 6/30/97 -0400, you wrote: >Hi gang, > I just got the current catalog of Mitcham Industries >(www.mitchamindustries.com). Among the large list of wild and wonderful >seismic equipment (some around $500,000) is "3 Hz l15B single phone >w/Muller clip". They have 50 for $25 ea. (This is more like my price >range.) They have a bunch more with higher freq. cut-offs. > I know nothing about these things but will buy one to play with. Two >questions:1. What is a Muller clip? and 2. Where can I get pin-outs etc. >so that I can hook it up. > I think that someone on this list stated that these things are verticals >unless otherwise labeled. >Bob Barns > >_____________________________________________________________________ > >Public Seismic Network Mailing List (PSN-L) > >To leave this list email listserver@............. with the body of the >message: leave PSN-L > > Dave A. Nelson 24 Jensen St., Green Is., Dunedin, South Is.. New Zealand. http://psn.quake.net/dave/home.htm Q-BIT'SLAWNo.9: INTERCHANGEABLEPARTS-WON'TBE Q-BIT'SLAWNo.10: ANY WIRING ERRORINANYCONSTRUCTIONWILLBEIN THE DIRECTION OF THE MOST DAMAGE Q-BIT'SLAWNo.13:IDENTICALPARTSAREN'T _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: David A Nelson Subject: Re: Geophones Date: Tue, 01 Jul 1997 12:50:52 +1200 Bob, further to my last message, Jim Croix, of Mitchum, informed me that they do have this model available SHEARWAVE 4.5 HZ LITTON Each $35.00 NOTE anything you see on their list stated as " SHEARWAVE " is a HORIZONTAL geophone at 4.5 Hz these are the same as the ones I am using here in New Zealand. Dave N. At 08:19 PM 6/30/97 -0400, you wrote: >Hi gang, > I just got the current catalog of Mitcham Industries >(www.mitchamindustries.com). Among the large list of wild and wonderful >seismic equipment (some around $500,000) is "3 Hz l15B single phone >w/Muller clip". They have 50 for $25 ea. (This is more like my price >range.) They have a bunch more with higher freq. cut-offs. > I know nothing about these things but will buy one to play with. Two >questions:1. What is a Muller clip? and 2. Where can I get pin-outs etc. >so that I can hook it up. > I think that someone on this list stated that these things are verticals >unless otherwise labeled. >Bob Barns Dave A. Nelson 24 Jensen St., Green Is., Dunedin, South Is.. New Zealand. http://psn.quake.net/dave/home.htm Q-BIT'SLAWNo.9: INTERCHANGEABLEPARTS-WON'TBE Q-BIT'SLAWNo.10: ANY WIRING ERRORINANYCONSTRUCTIONWILLBEIN THE DIRECTION OF THE MOST DAMAGE Q-BIT'SLAWNo.13:IDENTICALPARTSAREN'T _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: Doug Crice Subject: Re: Geophones Date: Mon, 30 Jun 1997 21:45:46 -0700 If you go to the geospace home page at http://www.geospacecorp.com/gs11d.htm you can see pictures of geophones. There's no scale in the picture, but they are about 1 inch diameter and 1.25 inches long. The schematic is a coil of wire (in a magnetic field) with two terminals. I'm afraid David used a New Zealand accent when describing a Mueller clip. A Mueller clip is one of those temporary test lead clips in the same class as "alligator clips", except that the teeth are bite shaped and made to connect with a contact that looks exactly like a coil spring. They are called Mueller clips after Mueller the manufacturer. They have red and black insulators and come in two different widths, which mate with two adjacent springs of different widths molded into a multi-conductor geophone cable. There is another common connector called the "split spring" or split ring. They look like those fuse holders you see nounted on circuit boards. There are also a family of waterproof connectors sometimes used in marshy situations. The reason geophones are described with their connector is so that the potential buyer can know if they will match the cables he has. Yes, geophones are vertical unless noted as horizontal or shear phones. Doug Crice _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: John Hernlund Subject: Re: Geophones Date: Mon, 30 Jun 1997 23:44:54 -0700 (MST) Robert, Could you send me the address of that company so that I could request a catalog? ****************************************************************************** John Hernlund E-mail: hernlund@....... WWW: http://www.mc.maricopa.edu/academic/phy_sci/Geology/hernlund/ ****************************************************************************** On Mon, 30 Jun 1997, Robert L Barns wrote: > Hi gang, > I just got the current catalog of Mitcham Industries > (www.mitchamindustries.com). Among the large list of wild and wonderful > seismic equipment (some around $500,000) is "3 Hz l15B single phone > w/Muller clip". They have 50 for $25 ea. (This is more like my price > range.) They have a bunch more with higher freq. cut-offs. > I know nothing about these things but will buy one to play with. Two > questions:1. What is a Muller clip? and 2. Where can I get pin-outs etc. > so that I can hook it up. > I think that someone on this list stated that these things are verticals > unless otherwise labeled. > Bob Barns > > _____________________________________________________________________ > > Public Seismic Network Mailing List (PSN-L) > > To leave this list email listserver@............. with the body of the > message: leave PSN-L > _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: Larry Cochrane Subject: Strange event... Date: Mon, 30 Jun 1997 23:58:36 -0700 Greetings, Yesterday my SDR systems when into alarm around 6/30/97 16:28 UTC. All of the USGS sensors that I monitor, and my S-G sensor, picked up the event. The problem is I can't find it on any of the Internet location services. The seismograms look like the P wave of a large teleseismic event with all of the waves near 2 hz but I can't see or find any matching S or long period surface waves. The closes event I can find is the Mb5.3 in Hawaii but it happened at 15:47. That's to early for the travel time of P wave and to high of a frequency for the S and long period surface waves. It's also to high of an amplitude for a 5.3 that far away. Anyone else get something around that time? This is a strange one... Regards, Larry Cochrane Redwood City, PSN _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: David A Nelson Subject: Re: Geophones Date: Wed, 02 Jul 1997 00:43:01 +1200 John they have a online catalog along with online ordering facilities at http://www.mitchamindustries.com Dave N. > Could you send me the address of that company so that I could request >a catalog? > >****************************************************************************** > > John Hernlund > E-mail: hernlund@....... > WWW: http://www.mc.maricopa.edu/academic/phy_sci/Geology/hernlund/ > >> Dave A. Nelson 24 Jensen St., Green Is., Dunedin, South Is.. New Zealand. http://psn.quake.net/dave/home.htm Q-BIT'SLAWNo.9: INTERCHANGEABLEPARTS-WON'TBE Q-BIT'SLAWNo.10: ANY WIRING ERRORINANYCONSTRUCTIONWILLBEIN THE DIRECTION OF THE MOST DAMAGE Q-BIT'SLAWNo.13:IDENTICALPARTSAREN'T _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: ct@....... (Charlie Thompson) Subject: Re: Strange event... Date: Tue, 01 Jul 1997 10:12:15 -0500 Larry, I did see something strange but I didn't note the time. I'll look again when I get home from work. Keep in mind that there was a volcanic event in Mexico City that spewed ashes 40,000 feet into the air and closed Mexico City Airport. I think the event was yesterday. -Charlie >Greetings, > >Yesterday my SDR systems when into alarm around 6/30/97 16:28 UTC. All of >the USGS sensors that I monitor, and my S-G sensor, picked up the event. >The problem is I can't find it on any of the Internet location services. >The seismograms look like the P wave of a large teleseismic event with all >of the waves near 2 hz but I can't see or find any matching S or long >period surface waves. The closes event I can find is the Mb5.3 in Hawaii >but it happened at 15:47. That's to early for the travel time of P wave and >to high of a frequency for the S and long period surface waves. It's also >to high of an amplitude for a 5.3 that far away. > >Anyone else get something around that time? This is a strange one... > >Regards, >Larry Cochrane >Redwood City, PSN > > >_____________________________________________________________________ > >Public Seismic Network Mailing List (PSN-L) > >To leave this list email listserver@............. with the body of the >message: leave PSN-L > > ------------------------------------------------------------------------- Charlie Thompson WB4HVD 30.112N 97.891W 800 Elliott Ranch Rd. Buda, TX 78610 http://www.onr.com/user/ct/ct.html Seismic Station .BUE _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: Dennis Leatart Subject: Re: Strange event... Date: Tue, 01 Jul 1997 08:53:22 -0700 I picked up this event also- I have not downloaded it yet-- but if anyone needs to look at it -- it is about 26K in bmp format. -- _____ __ | \.-----.-----.-----.|__|.-----. | -- | -__| | || ||__ --| |_____/|_____|__|__|__|__||__||_____| _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: "Phil Giannini" Subject: Strange Event Date: 1 Jul 1997 09:08:45 U REGARDING Strange Event Hi Guys, Yes I got it too, but didn't put it up yet because I was waiting for a comformation from one of the USGS sites. I will put it up tonight when I get home. Maybe if enough of us have it we can figure out where it came from. I received it on both of my sensors. Phil SFN SFZ _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: Charlie Plyler Subject: Re: Strange event... Date: Tue, 01 Jul 1997 12:25:18 -0400 Hello all, Whatever caused this event it was both electrical as well as seismic in nature. The 2hz wave form was very predominate on the East Coast. If anyone would desire an SDR file just let me know. Charlie Elfrad Group 35.728N 80.810W _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: "Martin Brewer" Subject: Re: Bermuda 'quake Date: Tue, 1 Jul 1997 18:24:08 -0300 Robert, I seem to have picked up a small event [M2.5] at 07/01/97, 21:12:36; 1.33 degrees (148km) from Bermuda [lat 32.3N, long 64.8W. Is there any chance you picked it up? Regards, Martin _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: Robert L Barns <75612.2635@..............> Subject: Re: Bermuda 'quake Date: Tue, 1 Jul 1997 21:47:00 -0400 Martin, I agree that it is handy to have others in the area to check out the weird ones. We have a different set of problems compared to that mob around the Pacific. On 6/24 I got one that looked pretty good. The internet report was Indonesia, org. 23:4:53 m6.1 at 1.8S and 127.8E. From me 9380 mi, 135.6 deg. (No P or S expected from that dist.) I calc. that the LQ here shou= ld be 24:16 (sic) but the biggest waves started here at about 24:18 to 24:2= 7. It was rather strange in that the largest waves were not much bigger tha= n what came before. From that far away, things get scrambled up. Bob Barns _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: Charlie & Terri Thompson Subject: Strange Event might be Hawaii Date: Tue, 01 Jul 1997 21:24:30 -0500 I recorded the strange event and went searching for a source.. here are the arrival times for the Hawaii Event into Buda, Texas. My peak waves arrived around 16:15 to 16:21 which is included in the arrival times below: DATE-(UTC)-TIME LAT LON DEPTH MAG Q COMMENTS 97/06/30 15:47:37 19.34N 155.06W 1.0 5.3Mb HAWAII delta azimuth (degrees clockwise from north) (deg) eq-to-station station-to-eq 52.56 66.5 272.1 travel arrival time # code time(s) dy hr mn sec 1 P 554.96 0 15 56 51 2 pP 555.28 0 15 56 52 3 sP 555.41 0 15 56 52 4 PcP 625.12 0 15 58 2 5 PP 673.94 0 15 58 50 6 PP 680.34 0 15 58 57 7 ScP 863.54 0 16 2 0 8 PcS 863.66 0 16 2 0 9 S 1003.67 0 16 4 20 10 pS 1004.06 0 16 4 21 11 sS 1004.21 0 16 4 21 12 PKiKP 1024.38 0 16 4 41 13 pPKiKP 1024.73 0 16 4 41 14 sPKiKP 1024.85 0 16 4 41 15 ScS 1146.10 0 16 6 43 16 SS 1223.23 0 16 8 0 17 SKiKP 1237.95 0 16 8 14 18 SS 1242.13 0 16 8 19 19 PKKPdf 1881.91 0 16 18 58 20 SKKPdf 2095.45 0 16 22 32 21 PKKSdf 2095.58 0 16 22 32 22 SKKSdf 2308.98 0 16 26 5 23 P'P'df 2384.51 0 16 27 21 24 P'P'bc 2401.56 0 16 27 38 25 P'P'ab 2426.24 0 16 28 3 26 S'S'df 3241.11 0 16 41 38 Thanks to John for the nice calculator! -Charlie Thompson Buda, Texas _ ________________________________________________ _ / ) | | ( \ / / | Charlie Thompson WB4HVD | \ \ _( (_ | _ e-mail: ct@....... _ | _) )_ (((\ \> |/ ) http://www.onr.com/user/ct/ct.html ( \| Subject: Re: Strange event... Date: Tue, 01 Jul 1997 19:51:43 -0700 At 11:58 PM 6/30/97 -0700, you wrote: >Greetings, > >Yesterday my SDR systems when into alarm around 6/30/97 16:28 UTC. All of >the USGS sensors that I monitor, and my S-G sensor, picked up the event. >The problem is I can't find it on any of the Internet location services. >The seismograms look like the P wave of a large teleseismic event with all >of the waves near 2 hz but I can't see or find any matching S or long >period surface waves. The closes event I can find is the Mb5.3 in Hawaii >but it happened at 15:47. That's to early for the travel time of P wave and >to high of a frequency for the S and long period surface waves. It's also >to high of an amplitude for a 5.3 that far away. > >Anyone else get something around that time? This is a strange one... > Larry- I am up the coast from you at Sea Ranch and I got it also. My computer is down but I got it on the drum recorder. The waves were of low frequency as you noted and I got them at about 16:05 (+- 5 minutes) UT. If you are interested, I can mail you the drum trace. George Bush _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: Larry Cochrane Subject: Re: Strange event... Date: Wed, 02 Jul 1997 00:59:54 -0700 Hi George, I think you got the surface waves of the Hawaii event. The event I was taking about happened 25 minutes later. I received the surface wave of the Hawaii event around 16:04 UTC. -Larry At 07:51 PM 7/1/97 -0700, you wrote: >I am up the coast from you at Sea Ranch and I got it also. My computer is >down but I got it on the drum recorder. The waves were of low frequency as >you noted and I got them at about 16:05 (+- 5 minutes) UT. If you are >interested, I can mail you the drum trace. > >George Bush > >_____________________________________________________________________ > >Public Seismic Network Mailing List (PSN-L) > >To leave this list email listserver@............. with the body of the >message: leave PSN-L > _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: Larry Cochrane Subject: More on the strange event... Date: Wed, 02 Jul 1997 01:24:58 -0700 Hi, I got this from David Wolny: >Date: Tue, 1 Jul 1997 10:25:17 -0600 (MDT) >From: David Wolny >To: cochrane@.............. >Subject: strange event >Hi Larry, >If you haven't gotten an answer yet, try this; >june 30 1997 16:29:04.4 38.2N 123.4 W Ml 2.8 depth 10 >You can get the info by phoning the NEIC and giving them the time that >you recorded the event. >Dave Thanks Dave, I think this is it. I was only 147km (79 miles) from the event and it would be big enough to register on my system at home and all of the USGS sensors I monitor. This event never showed up on any of the local (Berkeley or the Menlo Park USGS) finger servers. This is probably do to the fact that it was out in the ocean north west of me. The seismograms look different then a normal local 2.8, must be because of its location. Dave, did you get this info from the USGS phone system or somewhere on the NET? -Larry Cochrane Redwood City, PSN _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: gchantler@....... (Gary Chantler) Subject: Q's on 6/17/97 Date: Thu, 3 Jul 1997 08:19:19 -0800 Hi all, its been awhile since I've written. :-( I've been looking at some gravity data and I was wondering if something (quake) happened on the 17 of June???? I see the Washington (W. coast) quakes clearly in the trace(23,24th), but I also see something on the 17th (Wish I could be more specific) and thought someone might have the time to respond. I also have another question. Was there some talk awhile back about mercury pendulum seismometers???? You can write back to the list or to me at gchantler@....... _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: Robert L Barns <75612.2635@..............> Subject: Re: Geophones Date: Thu, 3 Jul 1997 19:59:45 -0400 John Hernlund, Mitcham Industries, PO Box 1175 Huntsville, TX 77342-1175 409-291-2277 Bob Barns _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: Robert L Barns <75612.2635@..............> Subject: Re: Bermuda 'quake Date: Thu, 3 Jul 1997 19:59:49 -0400 Martin, I see nothing at or near 7/1 21:12 although my noise level was high for= a few hours around that time. Bob _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: "Martin Brewer" Subject: Re: Bermuda 'quake Date: Thu, 3 Jul 1997 21:29:11 -0300 > From: Robert L Barns > I see nothing at or near 7/1 21:12 although my noise level was high for a > few hours around that time. Bob, Thanks for the response. How close would a M2.5 'quake have to be for you to see it (under normal circumstances)? regards, Martin _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: John Hernlund Subject: frequency, energy, and rupture length Date: Fri, 04 Jul 1997 21:30:49 -0700 (MST) I have a question for y'all. I was told once that the period of a seismic wave was approximately proportional to the rupture length of the event. In addition, it was inferred that the longer period quakes had a larger magnitude. I don't know a whole lot about this stuff yet and was wondering if anyone could elaborate on this for me. I know this much: The amount of energy released is proportional to the work done by the force on the system. Some of it is released as heat energy, and some as kinetic energy which it eventually transmits as various seismic waves due to the transfer of these kinetic displacements. As far as the forces go there is the tectonic or gravitational force that causes the initial stress, the force of static friction which is overcome by the stress, and then the kinetic friction as the displacement begins. A lot of energy can be released when this happens because the coefficient of static friction is always greater than the coefficient of kinetic friction. What I don't understand is: Why an increase in rupture length will cause a decrease in frequency. Is it because the movement will be impeded by the increased mass alongside the rupture therefore slowing the frequency? ****************************************************************************** John Hernlund E-mail: hernlund@....... WWW: http://www.mc.maricopa.edu/academic/phy_sci/Geology/hernlund/ ****************************************************************************** _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: David A Nelson Subject: Re: frequency, energy, and rupture length Date: Sat, 05 Jul 1997 17:45:23 +1200 this is a new one on me, John, In the many books read over the years never come across a comment like that, have you any references, were the comments to you from a scientific source??? the surface waves of an event are the ones with the real long preiods BUT!!! you get very large deep events where the surface waves are virtually non-existant but you still have a large rupture area Dave At 09:30 PM 7/4/97 -0700, you wrote: >I have a question for y'all. I was told once that the period of a seismic >wave was approximately proportional to the rupture length of the event. >In addition, it was inferred that the longer period quakes had a larger >magnitude. I don't know a whole lot about this stuff yet and was >wondering if anyone could elaborate on this for me. >What I don't understand is: > Why an increase in rupture length will cause a >decrease in frequency. Is it because the movement will be impeded by >the increased mass alongside the rupture therefore slowing the frequency? > > John Hernlund > E-mail: hernlund@....... Dave A. Nelson 24 Jensen St., Green Is., Dunedin, South Is.. New Zealand. http://psn.quake.net/dave/home.htm Q-BIT'SLAWNo.9: INTERCHANGEABLEPARTS-WON'TBE Q-BIT'SLAWNo.10: ANY WIRING ERRORINANYCONSTRUCTIONWILLBEIN THE DIRECTION OF THE MOST DAMAGE Q-BIT'SLAWNo.13:IDENTICALPARTSAREN'T _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: Robert L Barns <75612.2635@..............> Subject: Re: Bermuda 'quake Date: Sat, 5 Jul 1997 10:10:42 -0400 Martin, I est. that a 2.5 would have to be less than 15 miles for me to see it.= Bob Barns _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: Charlie & Terri Thompson Subject: Quake detection distance Date: Sat, 05 Jul 1997 09:20:04 -0500 The two Texas quakes that have occurred this year were approx Mag 3.5 and I recorded them at a distance of about 200 miles. So a Mag 2.5 at 20 miles seems to scale correctly. I have a quake distance detection map on my web page. The data for the map was based on a Lehman seismometer. http://www.onr.com/user/ct/ct.html -Charlie Thompson At 10:10 AM 7/5/97 -0400, you wrote: >Martin, > I est. that a 2.5 would have to be less than 15 miles for me to see it. >Bob Barns > >_____________________________________________________________________ > >Public Seismic Network Mailing List (PSN-L) > >To leave this list email listserver@............. with the body of the >message: leave PSN-L > > _ ________________________________________________ _ / ) | | ( \ / / | Charlie Thompson WB4HVD | \ \ _( (_ | _ e-mail: ct@....... _ | _) )_ (((\ \> |/ ) http://www.onr.com/user/ct/ct.html ( \| Charlie Thompson wrote: > Subject: Quake detection distance > Date: Saturday, July 05, 1997 11:20 AM > > The two Texas quakes that have occurred this year were approx Mag 3.5 > and I recorded them at a distance of about 200 miles. So a Mag 2.5 > at 20 miles seems to scale correctly on the same subject Bob Burns wrote > > I est. that a 2.5 would have to be less than 15 miles for me to see it. Thank you both for your comments. It looks as if my calibration is way out. Not surprising perhaps as the only confirmed 'quake I have detected is the Mag 6.6 event in the Aleutians on 17 June. Thanks Charlie for directing me to your web site, I shall visit with interest. Martin _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: John Hernlund Subject: linear response Date: Sat, 05 Jul 1997 23:00:12 -0700 (MST) I have been thinking ever since somebody posted here a while back on the best arrangement of a magnet-coil system. It seems for the most part that for small displacments in relation to the size of the coil and magnet that any non-linearity will be mostly negligible. I think this is one of the areas where large coil designs have an accuracy advantage when measuring larger displacements. Ideally, since the output is proportional to the cross product of the relative velocity and the magnetic field a single wire should be arranged so that it is both perpendicular to the direction of motion and the the magnetic field lines. But applying the correct geometry to a coil is a bit more involved. It seems like the best way is to have an arrangement like this: Use sets of flat long magnets that are magnetized thickwise, not lengthwise (one or more set depending). Set up some on the inside of a coil so that the south pole faces point outwards from the center of the circle thus formed. Orient these as close to the inside face of the coils as possible. Next, put matching pairs of magnets around the outside of the coil as close as possible to each one inside with the north poles facing inward toward in center of the circular coil. Now this would have to be oriented so that the magnets would be stationary and the coil moving along its symmetric axis, or vice versa. The theory for this is that the net magnetic flux for the cylinder walls will be more positive or negative, provided that the coil is not taller than the magnets. In this way, the field lines from the north poles of the inner magnets will be repulsed and tend toward the top and bottom of the coil. Is this correct? Has anyone else tried anything similar to this??? ****************************************************************************** John Hernlund E-mail: hernlund@....... WWW: http://www.mc.maricopa.edu/academic/phy_sci/Geology/hernlund/ ****************************************************************************** _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: Jim Hannon Subject: Re: linear response Date: Sun, 06 Jul 1997 07:50:26 -0500 John Hernlund wrote: > > > > The theory for this is that the net magnetic flux for the cylinder > walls will be more positive or negative, provided that the coil is not > taller than the magnets. In this way, the field lines from the north > poles of the inner magnets will be repulsed and tend toward the top and > bottom of the coil. > > Magnetics was one of the more difficult subjects I had in school. It is so hard to visulize what those magnetic field lines are going to do. It seems that the coil and magnet arrangment for a hombuilt seismograph has at least these requirements. 1. A somewhat linear response to the velocity of the coil. 2. As much voltage output as possible. 3. Be relativly easy to make with materials that can be obtained inexpensively. Requirement number 3 seems to be at the heart of a lot of the struggling that goes into a design. One thing that seems to be common in the design of commercial electromagnetic devices is that they use a single magnet and provide a path from one pole of the magnetic to the other, for the magnetic flux with soft iron or some other permeable material. The coil is then placed in a small gap in this magnetic circuit. Magnetic flux being compared to electric current and any resistance to the flux, such as air in the path, causes the field in the gap to be weaker. Look at the magnetic design of a loudspeaker or the voice coil actuator in a computer hard drive. I think the magnets in a hard drive voice coil actuator would make a great seismograph. -- Jim Hannon http://soli.inav.net/~jmhannon/ 42,11.90N 91,39.26W _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: Charlie & Terri Thompson Subject: Unidentified Event Date: Sun, 06 Jul 1997 10:13:57 -0500 Looks like USGS missed a small event at: 7/6/97 1:36 UTC (approx mag 4.8) about 1500 miles from Buda, Texas. This was probably Mexico or the Carribbean. Did anyone else record an event at or near this time? thanks, Charlie _ ________________________________________________ _ / ) | | ( \ / / | Charlie Thompson WB4HVD | \ \ _( (_ | _ e-mail: ct@....... _ | _) )_ (((\ \> |/ ) http://www.onr.com/user/ct/ct.html ( \| Subject: Re: linear response Date: Sun, 06 Jul 1997 07:30:28 -0700 Hi Jim & John Since I wrote to origninal note I tried a couple of coil/magnetic arrangements. The one that worked the best with the minimum # of parts was to orientate the coil pertendicular to the direction of motion and place a cylindrical magnet near ,but not inside, the coil. The flux lines are crossing the coil going from pole to pole. I think that the idea John suggested would be stronger; However, I have had problems in the past placing magnets next to each other that were oriented the same way. They tend to repel each other. I have also thought a hard drive coil would be great also. I would love to find a NG one somewhere to play with. But I think hard drives can also come with stepper motors. Any ideas as to which have stepper motors and which have voice coil? Barry Jim Hannon wrote: > Look at the > magnetic design of a loudspeaker or the voice coil actuator in a > computer hard drive. I think the magnets in a hard drive voice coil > actuator would make a great seismograph. > -- > Jim Hannon > http://soli.inav.net/~jmhannon/ > 42,11.90N 91,39.26W > _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: roger baker Subject: Re: linear response Date: Sun, 6 Jul 1997 11:34:22 -0500 (CDT) Friends, The optimum requirements for a force balancing setup are distinctly different than those for detection of motion, least this might be an issue. Magnetic circuits weaken rapidly as any gap increases and this has caused loudspeakers to be designed the way they are with narrow circular gaps just wide enough to admit a light coil. But since the design has been optimized for low weight and high power its hard to get many turns into this gap for good voltage output. You can design the coil around the magnets or vice versa, but here you generally want lots of turns, so a pancake sort of coil has evolved to balance lots of turns with a modest magnet gap. Of course you could double the sensitivity by mountting a second magnet on the opposite side of the coil with the poles reversed. This might improve linearity if arranged so that when one half signal strengthens, the other attenuates. My suggestion however would be to take apart a geophone and remount the magnet and coil on a Lehman, but without the geo's spring of course. I offer this suggestion in light of the fact that geophones have been carefully engineered to do about exactly what you want to do in terms of generating voltage from small motions. You can all get ready to flame me for saying this, but my opinion is that coils may be obsolete as displacement transducers on the best long period instruments and may be replaced by optical and capacitative transducers that have as much sensitivity but are DC; they do not weaken in signal strength as velocity increases with long periods. From the time of Galitizen, magnetics has been favored because it was cheap and easy and sensitive and fit in with the technology of the day. Now things are different. Force feedback has different requirements and as a method of achieving the desired results, it is the only game in town. Since the displacement is miniscule, theoretically zero in fact, there are no magnetic non-linearities to fight and a coil attracts and repels equally with a reverse in voltage so long as nothing moves. I figure that so long as you have to have some mass, that mass might just as well be a ceramic magnet. I use a flat magnet and a flat coil made of fine wire wound with wire wet with a little epoxy so the coil holds its shape.The two are mounted facing each other with a narrow gap. --Yours, Roger Baker _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: Jim Hannon Subject: Re: linear response Date: Sun, 06 Jul 1997 12:12:14 -0500 barry lotz wrote: > But I think hard drives can also come with stepper motors. > Any ideas as to which have stepper motors and which have voice coil? > Barry > > message: leave PSN-L I don't know by brand and model but most of the newer ones have evolved to the voice coil arrangment. We get a lot of dead drives at work and sometimes the PC repair guy will let someone have the old drive to salvage. I haven't gotten any myself so I don't have any to play with. -- Jim Hannon http://soli.inav.net/~jmhannon/ 42,11.90N 91,39.26W _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: barry lotz Subject: Re: linear response Date: Sun, 06 Jul 1997 11:47:11 -0700 Roger Even though my Lehman has given results to my satisfaction over the years, I agree and force balance has my attention right now. You mentioned they are DC, I assume you mean response wise since both types you mentioned require a AC excition signal. I am still using a coil as the restoring force. To get around the high frequencies produced by acceleration measurements I plan to integrate the digital signal mathematically ,in real time, to velocity. I think this could be accomplished by simply adding the readings in time. The readings would have to be adjusted to be centered around zero to avoid overflow. Barry >roger baker wrote: > > You can all get ready to flame me for saying this, but my opinion is that > coils may be obsolete as displacement transducers on the best long period > instruments and may be replaced by optical and capacitative transducers > that have as much sensitivity but are DC; they do not weaken in signal > strength as velocity increases with long periods. From the time of > Galitizen, magnetics has been favored because it was cheap and easy and > sensitive and fit in with the technology of the day. Now things are > different. > > Force feedback has different requirements and as a method of achieving > the desired results, it is the only game in town. Since the displacement > is miniscule, theoretically zero in fact, there are no magnetic > non-linearities to fight and a coil attracts and repels equally with > a reverse in voltage so long as nothing moves. I figure that so long as > you have to have some mass, that mass might just as well be a ceramic > magnet. I use a flat magnet and a flat coil made of fine wire wound with > wire wet with a little epoxy so the coil holds its shape.The two are > mounted facing each other with a narrow gap. > > --Yours, Roger Baker > _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: Al Allworth Subject: Re: linear response Date: Sun, 6 Jul 1997 12:49:23 -0700 At 07:50 AM 7/6/97 -0500, you wrote: >John Hernlund wrote: I think the magnets in a hard drive voice coil >actuator would make a great seismograph. >-- >Jim Hannon Hi Jim and all, I have saved the head drive assemblies from several hard drives but haven't put anything together yet. I think the parts from the 3 1/2 inch drives are all voice coil type. The stepping motors were too slow for modern computers. I have seen the inside of 2 1/2 inch drives used in laptop computers at trade shows and think they would be great for making a sensor. They use rare earth magnets that are so strong that one can't pull them off of a flat piece of iron by hand. New subject: Has any experience with the use of strain guages in making seismometers? They are true displacement devices and can be easily constructed. Cost is low also. I have designed them into electronic scales and felt they were quite stable. You connect them as a bridge so the thermal effects cancel. It's also possible to connect them so you can get two axis output. ____________________________________________________________________________ Al Allworth, Gold Beach, OR aallworth@........ _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: Ron Westfall Subject: Re: Unidentified Event Date: Sun, 06 Jul 1997 13:59:03 -0700 The NEIC is currently showing that an M4.8 occurred near the coast of Nicaragua (11.61N, 86.89W) at 1:36:39. That was probably it. Did anybody else see a large event around 10:00 UTC 07/06/97? I had what looked like surface waves coming in for an hour and a half. The NEIC is showing an M6.5 near the coast of Chile (29.99S, 71.68W) at 9:54:02. I wonder if that's it? This is my first experience seeing surface waves. Does anybody have a sense of how large a quake has to be at a given distance before you will pick up the surface waves? Ron Westfall westfall@...... Charlie & Terri Thompson wrote: > Looks like USGS missed a small event at: > > 7/6/97 1:36 UTC (approx mag 4.8) about 1500 miles > from Buda, Texas. > > This was probably Mexico or the Carribbean. > > Did anyone else record an event at or near this time? _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: Jean-Jacques HUNSINGER Subject: Re: Unidentified Event Date: Sun, 06 Jul 1997 23:57:19 +0200 Ron Westfall wrote: ...... > Did anybody else see a large event around 10:00 UTC 07/06/97? I had > what looked like surface waves coming in for an hour and a half. The > NEIC is showing an M6.5 near the coast of Chile (29.99S, 71.68W) at > 9:54:02. I wonder if that's it? > ..... Hi, I got this event here in France at 10h28 UTC Regards. _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: Edward Cranswick Subject: Re: Quake detection distance Date: Sun, 06 Jul 1997 16:10:20 -0600 Charlie- Very interesting map you have made. Station noise will be a limiting factor of recordings of local/regional events that are dominated by high frequencies. -Edward Charlie & Terri Thompson wrote: > > The two Texas quakes that have occurred this year were approx Mag 3.5 > and I recorded them at a distance of about 200 miles. So a Mag 2.5 > at 20 miles seems to scale correctly. I have a quake distance detection > map on my web page. The data for the map was based on a Lehman seismometer. > > http://www.onr.com/user/ct/ct.html > > -Charlie Thompson > > At 10:10 AM 7/5/97 -0400, you wrote: > >Martin, > > I est. that a 2.5 would have to be less than 15 miles for me to see it. > >Bob Barns > > > >_____________________________________________________________________ > > > >Public Seismic Network Mailing List (PSN-L) > > > >To leave this list email listserver@............. with the body of the > >message: leave PSN-L > > > > > > _ ________________________________________________ _ > / ) | | ( \ > / / | Charlie Thompson WB4HVD | \ \ > _( (_ | _ e-mail: ct@....... _ | _) )_ > (((\ \> |/ ) http://www.onr.com/user/ct/ct.html ( \| (\\\\ \_/ / Latitude 30.112 N \ \_/ ////) > \ / Longitude 97.891 W \ / > \ _/ Seismic Station .BUE \_ / > / / |________________________________________________| \ \ > / / \ \ > > _____________________________________________________________________ > > Public Seismic Network Mailing List (PSN-L) > > To leave this list email listserver@............. with the body of the > message: leave PSN-L -- Edward Cranswick Tel: 303-273-8609 US Geological Survey, MS 966 Fax: 303-273-8600 PO Box 25046, Federal Center cranswick@........ Denver, CO 80225-0046 USA E.M. Forster said, "Only connect". _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: Charlie & Terri Thompson Subject: Re: Quake detection distance Date: Sun, 06 Jul 1997 21:28:31 -0500 In-Reply-To: <33C017CC.E82@........> References: <3.0.1.16.19970705092004.2c974e84@.......> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" I can't take credit for the map...one of our PSN members in San Diego generated it for me based on his Lehman data and my Lat/Lon. It does however, correlate well with my Lehman data. -Charlie At 04:10 PM 7/6/97 -0600, you wrote: >Charlie- >Very interesting map you have made. Station noise will be a limiting >factor of recordings of local/regional events that are dominated by high >frequencies. >-Edward > >Charlie & Terri Thompson wrote: >> >> The two Texas quakes that have occurred this year were approx Mag 3.5 >> and I recorded them at a distance of about 200 miles. So a Mag 2.5 >> at 20 miles seems to scale correctly. I have a quake distance detection >> map on my web page. The data for the map was based on a Lehman seismometer. >> >> http://www.onr.com/user/ct/ct.html >> >> -Charlie Thompson >> >> At 10:10 AM 7/5/97 -0400, you wrote: >> >Martin, >> > I est. that a 2.5 would have to be less than 15 miles for me to see it. >> >Bob Barns >> > >> >_____________________________________________________________________ >> > >> >Public Seismic Network Mailing List (PSN-L) >> > >> >To leave this list email listserver@............. with the body of the >> >message: leave PSN-L >> > >> > >> >> _ ________________________________________________ _ >> / ) | | ( \ >> / / | Charlie Thompson WB4HVD | \ \ >> _( (_ | _ e-mail: ct@....... _ | _) )_ >> (((\ \> |/ ) http://www.onr.com/user/ct/ct.html ( \| > (\\\\ \_/ / Latitude 30.112 N \ \_/ ////) >> \ / Longitude 97.891 W \ / >> \ _/ Seismic Station .BUE \_ / >> / / |________________________________________________| \ \ >> / / \ \ >> >> _____________________________________________________________________ >> >> Public Seismic Network Mailing List (PSN-L) >> >> To leave this list email listserver@............. with the body of the >> message: leave PSN-L > >-- >Edward Cranswick Tel: 303-273-8609 >US Geological Survey, MS 966 Fax: 303-273-8600 >PO Box 25046, Federal Center cranswick@........ >Denver, CO 80225-0046 USA E.M. Forster said, "Only connect". > >_____________________________________________________________________ > >Public Seismic Network Mailing List (PSN-L) > >To leave this list email listserver@............. with the body of the >message: leave PSN-L > > _ ________________________________________________ _ / ) | | ( \ / / | Charlie Thompson WB4HVD | \ \ _( (_ | _ e-mail: xctx@....... _ | _) )_ (((\ \> |/ ) http://www.onr.com/user/ct/ct.html ( \| Subject: Re: Quake detection distance Date: Sun, 06 Jul 1997 21:31:58 -0500 In-Reply-To: <33C017CC.E82@........> References: <3.0.1.16.19970705092004.2c974e84@.......> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Proper credit for the generation of the map should (I think) go to: Fred Bruenjes in San Diego. Thanks Fred! -Charlie At 04:10 PM 7/6/97 -0600, you wrote: >Charlie- >Very interesting map you have made. Station noise will be a limiting >factor of recordings of local/regional events that are dominated by high >frequencies. >-Edward > >Charlie & Terri Thompson wrote: >> >> The two Texas quakes that have occurred this year were approx Mag 3.5 >> and I recorded them at a distance of about 200 miles. So a Mag 2.5 >> at 20 miles seems to scale correctly. I have a quake distance detection >> map on my web page. The data for the map was based on a Lehman seismometer. >> >> http://www.onr.com/user/ct/ct.html >> >> -Charlie Thompson >> >> At 10:10 AM 7/5/97 -0400, you wrote: >> >Martin, >> > I est. that a 2.5 would have to be less than 15 miles for me to see it. >> >Bob Barns >> > >> >_____________________________________________________________________ >> > >> >Public Seismic Network Mailing List (PSN-L) >> > >> >To leave this list email listserver@............. with the body of the >> >message: leave PSN-L >> > >> > >> >> _ ________________________________________________ _ >> / ) | | ( \ >> / / | Charlie Thompson WB4HVD | \ \ >> _( (_ | _ e-mail: ct@....... _ | _) )_ >> (((\ \> |/ ) http://www.onr.com/user/ct/ct.html ( \| > (\\\\ \_/ / Latitude 30.112 N \ \_/ ////) >> \ / Longitude 97.891 W \ / >> \ _/ Seismic Station .BUE \_ / >> / / |________________________________________________| \ \ >> / / \ \ >> >> _____________________________________________________________________ >> >> Public Seismic Network Mailing List (PSN-L) >> >> To leave this list email listserver@............. with the body of the >> message: leave PSN-L > >-- >Edward Cranswick Tel: 303-273-8609 >US Geological Survey, MS 966 Fax: 303-273-8600 >PO Box 25046, Federal Center cranswick@........ >Denver, CO 80225-0046 USA E.M. Forster said, "Only connect". > >_____________________________________________________________________ > >Public Seismic Network Mailing List (PSN-L) > >To leave this list email listserver@............. with the body of the >message: leave PSN-L > > _ ________________________________________________ _ / ) | | ( \ / / | Charlie Thompson WB4HVD | \ \ _( (_ | _ e-mail: xctx@....... _ | _) )_ (((\ \> |/ ) http://www.onr.com/user/ct/ct.html ( \| Proper credit for the generation of the map >should (I think) go to: > > Fred Bruenjes > >in San Diego. > >Thanks Fred! That's correct, and you're welcome! I just thought that some people might be interested in the story behind the map. See http://icse1.ucsd.edu/~mbruenje/seismo/data.html if you're interested. Also, I've been meaning to update the map - the one Charlie has (and the one on my web site) was based on only about 3 months of data. Now that my Lehman has been running for around 10 months, I have a much better idea of its' capabilities. To make a long story short, I think the circles on the maps need to be a wee bit farther out, since lately I have been getting quakes from outside the circles (most recently, last week's 5.3 in Hawaii). Below are some real numbers derived from my distance vs magnitude plot (see the web page above), which is based on observations of around 500 earthquakes. Of the 500 quakes I searched for in my recordings over a 10 month period, about 130 were actually detected. Magnitude: Distance: ---------- --------- 2.0 40 mi 2.5 110 mi 3.0 140 mi 3.5 200 mi 4.0 300 mi 4.5 700 mi 5.0 1,300 mi 5.5 2,500 mi 6.0 4,500 mi 6.5 10,000 mi 7.0+ Anywhere on Earth By 'distance' I mean the maximum distance at which the effects of the quake can be seen by a standard Lehman-style seismometer in the middle of a large city (in my case, San Diego). People in quieter locations, or with better equipment, can expect to do better. I have noticed that Karl Cunningham, who is a few miles east of me, has a lower background noise - his earthquake traces stand out more and look cleaner than mine. So he can probably do better than this table suggests. I have also noticed that you really need higher sample rates to get local quakes. I had been using 1 sample/second for a long time and recently upgraded to 5 samples/s and this has made an incredible difference in the reception of local quakes. Now I can actually see the P and S waves! Fred Bruenjes ------------------------------------------ Fred Bruenjes mbruenje@........ http://icse1.ucsd.edu/~mbruenje/index.html _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: Norman Davis WB6SHI Subject: Norcal network and detection Date: Sun, 06 Jul 1997 06:53:45 Can anyone point me to the Norcal Network, The frequencies they are on and a means to detect the sites. I have done this a few years back on the single axis sites, but the one I can hear at my new location in Shingle Springs, Ca is a 3 axis site with 3 tones. Any one have a skematic on a decoder. Norman Davis WB6SHI Email normd@............. Shingle Springs, Ca, USA _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: Mike Stickney Subject: Re: frequency, energy, and rupture length Date: Mon, 7 Jul 97 08:12:28 MDT At 09:30 PM 7/4/97 -0700, you wrote: >What I don't understand is: > Why an increase in rupture length will cause a >decrease in frequency. Is it because the movement will be impeded by >the increased mass alongside the rupture therefore slowing the frequency? > > >****************************************************************************** > > John Hernlund > E-mail: hernlund@....... > WWW: http://www.mc.maricopa.edu/academic/phy_sci/Geology/hernlund/ > >****************************************************************************** Hi John: I haven't seen much response to your querry so I'll take a stab at it. Large earthquakes do generate lots of high frequency energy but they also generate low frequency energy not present in smaller quakes. Large quakes generate low frequencies because the long dimensions of the fault that slipped can radiate waves with long wavelengths. For distant large earthquakes, significant amounts of the high frequency energy has attenuated but most of the low frequency energy remains unattenuated and can be recorded by your seismograph. The lowest frequency generated by an earthquake is proportional to fault rupture dimensions. -Mike Stickney Montana Bureau of Mines and Geology Butte MT _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: "Charles R. Patton" Subject: Re: linear response Date: Mon, 07 Jul 1997 09:54:12 -0700 A few notes on disk drives (I work in the industry). 1) You can pretty much tell the stepper drives because the stepper motors were mounted on the outside at one end. The end of the shaft was outside and had a "flag" on it for an opto-interrupter in order to locate track zero. The disk motor had an external flywheel/drive magnets with a small inductive sense of a small hole drilled in the rim. The drive coils underneath that flywheel had hall effect sensors for position sense. (All my experience is with Western Digital drives, but most others are similar at the same time frame.) We quit manufacturing stepper drives about 7 or 8 years ago and went totally to voice coil designs. 2) Voice coil designs have nothing except the circuit board on the outside. (This is because they must be sealed against dust due to the low flying heights of the heads.) On 3 1/2 drive designs the actuator is a rotary design with the heads about 2" from the pivot and the center of the voice coil about 1" from the pivot. If you imagine the coil as a flat trapezoidal shaped (like a pie wedge) with the narrow end of the wedge pointing to the pivot point. This moves over the flat magnet which is poled with one area N and one area S. The coil moves close over the surface of this magnet. Then on top of this is placed a 'keeper' or 'flux return plate' which returns the flux to the other side of the magnet. Some designs use two magnets or even four for very powerful (read fast access times) accelerations. One of the key design points is maintain the field evenly over the stroke. Uneven fields affects the ability of the control system. So as for some stakes in the ground: This field uniformity is in the 10% range and a typical BEMF would be 40mV per inch per second of the coil movement. |------------------------------------| |--------- upper flux plate----------| |------------------------------------| |--| |--| |--| |XXX| |***| |--| |--| |XXX| coil |***| |--| Sliced |--| ^ | |--| End View of coil in field |--| | field | |--| Along With Flux Plates |--| |N vS |--| (Coil moves side-to-side |--| |**************************| |--| this illustration.) |--| |********magnet************| |--| |------------------------------------| |------- lower flux plate -----------| |------------------------------------| Charles R. Patton patton@......... _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: Jim Hannon Subject: Re: Quake detection distance Date: Mon, 07 Jul 1997 17:24:44 -0500 This map really makes it easy to visulize the quake distances. It looks a lot like a satellite visability map. One thing that I think would be a useful addition is showing the shadow zone for the P waves on the same map. -- Jim Hannon http://soli.inav.net/~jmhannon/ 42,11.90N 91,39.26W _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: Edward Cranswick Subject: Re: frequency, energy, and rupture length Date: Mon, 07 Jul 1997 21:13:19 -0600 John- With respect to why the dominant period of the source ground motions generated by an earthquake is proportional to the rupture length, consider the fault as an antenna that radiates seismic waves. Imagine the fault to be divided into a set of segments that are some fraction of the total fault length. In general, wavelengths equal to these segment lengths will tend to destructively interfere with each other at some distance from the fault, and their sum will be less than the contribution of one segment times the number of segments. For wavelengths similar to the total fault length, the fault will appear to be a single coherent radiator and there will be no destructive interference at that period, which will thus appear to be a maximum. Jim Brune has written the classic paper on the subject: Brune, J.N. (1970). Tectonic stress and the spectra of seismic shear waves from earthquakes, J. Geophys. Res., v. 75, pp. 4997-5009. -Edward John Hernlund wrote: > > I have a question for y'all. I was told once that the period of a seismic > wave was approximately proportional to the rupture length of the event. > In addition, it was inferred that the longer period quakes had a larger > magnitude. I don't know a whole lot about this stuff yet and was > wondering if anyone could elaborate on this for me. > > I know this much: > The amount of energy released is proportional to the work done by the > force on the system. Some of it is released as heat energy, and some as > kinetic energy which it eventually transmits as various seismic waves due > to the transfer of these kinetic displacements. As far as the forces go > there is the tectonic or gravitational force that causes the initial > stress, the force of static friction which is overcome by the stress, and > then the kinetic friction as the displacement begins. A lot of energy > can be released when this happens because the coefficient of static > friction is always greater than the coefficient of kinetic friction. > > What I don't understand is: > Why an increase in rupture length will cause a > decrease in frequency. Is it because the movement will be impeded by > the increased mass alongside the rupture therefore slowing the frequency? > > ****************************************************************************** > > John Hernlund > E-mail: hernlund@....... > WWW: http://www.mc.maricopa.edu/academic/phy_sci/Geology/hernlund/ > > ****************************************************************************** > > _____________________________________________________________________ > > Public Seismic Network Mailing List (PSN-L) > > To leave this list email listserver@............. with the body of the > message: leave PSN-L -- Edward Cranswick Tel: 303-273-8609 US Geological Survey, MS 966 Fax: 303-273-8600 PO Box 25046, Federal Center cranswick@........ Denver, CO 80225-0046 USA E.M. Forster said, "Only connect". _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: Larry Cochrane Subject: Re: Norcal network and detection Date: Mon, 07 Jul 1997 21:31:17 -0700 At 06:53 AM 7/6/97, Norman wrote: > Can anyone point me to the Norcal Network, The frequencies they are on and >a means to detect the sites. Unfortunately the frequencies and tone channels are not on the Net that I know of. This info is kept in a book in the basement of the local (Menlo Park) USGS office. They are VERY reluctant to give out this info because they are afraid of people stilling their equipment. BUT the latitude and longitude of the stations are on the Web at http://quake.geo.berkeley.edu/ncedc/station.info.html, so go figure.... The lat/long info is down to 4 decimal points (a few feet?) so anyone with a GPS receiver could find them. There are several ways to figure out the station you are receiving. You can go over to the Menlo Park USGS office and see if they will tell you the info. If you have a RF frequency and tell them you are with the PSN they might tell you what tone as what. Most of the channels are short period high gain vertical sensors. But they do have some short period horizontal and other types of sensors around. Also, a RF link may be a repeater for other stations sensor. You can figure out the location of the sensors two other ways. Both use known locations of events. By using the P and S wave distance you can plot on a map several known local events. This way you should be able to figure out the location, but, reading the P and S waves takes some practice. The other way requires that you have accurate timing, down to about 10 ms. At the Berkeley.edu site you can get the P arrival times for local events. By looking at the list of arrival times for each station you should be able to fine one that matches the unknown station. >I have done this a few years back on the >single axis sites, but the one I can hear at my new location in Shingle >Springs, Ca is a 3 axis site with 3 tones. Any one have a skematic on a >decoder. I sell a demodulator card that can be used to receive the info (see http://psn.quake.net/telebrd.html). The advantage of my card is it can receive any one of the 8 tones, used by the USGS, by simple setting a dip switch on the board. The card connects up to the audio output of a police scanner (or other receiver) and produces a +- 5 volt signal than can then go into a A/D card or chart recorder. Hope this helps... -Larry Cochrane _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: mbruenje@........ (Fred Bruenjes) Subject: Re: Quake detection distance Date: Tue, 08 Jul 1997 00:04:07 -0700 >One thing that I think would be >a useful addition is showing the shadow zone for the P waves on the same >map. Excellent suggestion. I've now redrawn the map, with my new data, and with the P wave shadow zone. It's kind of neat to be able to see just which areas this covers. I also made up several versions of the map, each for a different place around the world, so everybody can get an idea of what it looks like at their location. The URL again, in case anyone missed it: http://icse1.ucsd.edu/~mbruenje/seismo/data.html The new maps are about halfway down the page. Fred ------------------------------------------ Fred Bruenjes mbruenje@........ http://icse1.ucsd.edu/~mbruenje/index.html _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: "Martin Brewer" Subject: Building a Rigid Seismometer Date: Tue, 8 Jul 1997 19:57:30 -0300 Hi everyone, Now that the Bermuda N-S, home-built Lehman instrument seems to be working, I am about to start building its E-W sibling. Being cramped for useable space, my idea is to build a tripod around the N-S instrument and place an E-W oriented sensor on a raised platform above the N-S instrument. I need some advice on the engineering so that the structure is rigid enough not to have unwanted resonance and can track 'quakes accurately. I am thinking of building a tripod about 4 feet high to support the base of the sensor. Can I use galvanized pipe (given that it will be built around the N-S ground level sensor)? Could I use concrete pillars? If so what diameter should they be? Can the pillars be reinforced by ordinary galvanized re-bar without affecting the N-S instrument which will have magnet and coil within, say, a foot of the nearest pillars? Does anyone have any working designs for instruments built four feet (plus or minus) above the ground? One last question. Does such an elevated support need to be bolted to the ground? From earlier correspondence on the PSN, I conclude that it is totally unnecessary. My "Doubting Thomas" of a brother-I- law (who is the nuts and bolts man on this project) thinks differently. I would be grateful for any and all comments. Regards, Martin _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: "Martin Brewer" Subject: Surface Waves Date: Tue, 8 Jul 1997 22:27:09 -0300 Bermuda has picked up two sets of waves 13 minutes apart. I thought it might be some major event in the Aleutians but no follow through. In any case the waves are long period. Has anyone picked up the event(s): Long waves in two separate packets at 01:23 UTC and 01:36 UTC arrival times at Bermuda? Regards, Martin _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: Charlie & Terri Thompson Subject: Re: Surface Waves Date: Tue, 08 Jul 1997 23:17:53 -0500 Martin, Dr.John Lahr's wave arrival time prediction web page can help you identify the Bermuda arrival times of various waves..try the following URL: http://www.giseis.alaska.edu/Input/lahr/artim.html Operation is reasonably self-explanatory. A wonderful tool! -Charlie At 10:27 PM 7/8/97 -0300, you wrote: >Bermuda has picked up two sets of waves 13 minutes apart. I thought it >might be some major event in the Aleutians but no follow through. In any >case the waves are long period. Has anyone picked up the event(s): Long >waves in two separate packets at 01:23 UTC and 01:36 UTC arrival times at >Bermuda? >Regards, >Martin > >_____________________________________________________________________ > >Public Seismic Network Mailing List (PSN-L) > >To leave this list email listserver@............. with the body of the >message: leave PSN-L > > _ ________________________________________________ _ / ) | | ( \ / / | Charlie Thompson WB4HVD | \ \ _( (_ | _ e-mail: xctx@....... _ | _) )_ (((\ \> |/ ) http://www.onr.com/user/ct/ct.html ( \| Subject: Re: Building a Rigid Seismometer Date: Wed, 09 Jul 1997 10:14:25 -0600 Content-Transfer-Encoding: 7bit Martin- I think it is an EXTREMELY BAD idea to place the seismometer on any kind of platform above the ground. The structure of the platform will tend to produce amplifications and resonances that will significantly compound the complexities that already exist from site response and instrument response. So avoid it if you can. -Edward Martin Brewer wrote: > > Hi everyone, > > Now that the Bermuda N-S, home-built Lehman instrument seems to be working, > I am about to start building its E-W sibling. Being cramped for useable > space, my idea is to build a tripod around the N-S instrument and place an > E-W oriented sensor on a raised platform above the N-S instrument. > > I need some advice on the engineering so that the structure is rigid enough > not to have unwanted resonance and can track 'quakes accurately. > > I am thinking of building a tripod about 4 feet high to support the base of > the sensor. Can I use galvanized pipe (given that it will be built around > the N-S ground level sensor)? Could I use concrete pillars? If so what > diameter should they be? Can the pillars be reinforced by ordinary > galvanized re-bar without affecting the N-S instrument which will have > magnet and coil within, say, a foot of the nearest pillars? > > Does anyone have any working designs for instruments built four feet (plus > or minus) above the ground? > > One last question. Does such an elevated support need to be bolted to the > ground? From earlier correspondence on the PSN, I conclude that it is > totally unnecessary. My "Doubting Thomas" of a brother-I- law (who is the > nuts and bolts man on this project) thinks differently. > > I would be grateful for any and all comments. > > Regards, > Martin > > _____________________________________________________________________ > > Public Seismic Network Mailing List (PSN-L) > > To leave this list email listserver@............. with the body of the > message: leave PSN-L -- Edward Cranswick Tel: 303-273-8609 US Geological Survey, MS 966 Fax: 303-273-8600 PO Box 25046, Federal Center cranswick@........ Denver, CO 80225-0046 USA E.M. Forster said, "Only connect". _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: Robert L Barns <75612.2635@..............> Subject: Surface Waves Date: Wed, 9 Jul 1997 15:07:58 -0400 Martin, I looked in my DSR files for 7/4-7/8 (today at 18:00 UTC) and see nothi= ng around 1:30 for any of these days. I checked them all since you did not state a date. Bob Barns = _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: Robert L Barns <75612.2635@..............> Subject: Quake detection dist. Date: Wed, 9 Jul 1997 15:07:53 -0400 Hi gang, The info at Charlie's page (www.onr.com/user/ct/ct.html) is very interesting esp. the photos and drawing of his Lehman. The use of Dexion= is a good idea. = The several messages discussing 'quake detection distance ignores an important factor. A vertical seismometer is omnidirectional and this factor is irrelevant. However, most of us use horizontal (e.g., Lehman &= S-G) seismometers. They have a bi-directional response. Ground motion perpendicular to the boom will give a maximum output but motion along the= boom will produce zero output (at least in theory). = The output should be close to proportional to the cosine of the angle between the incoming wave and the boom. This factor is also ignored in SDR and WINQUAKE which uses only the distance and an empirical factor to estimate the magnitude. = Also, it would be handy if WINQUAKE showed the azimuth the quake a= s well as the azi the 'quake. The azi to the quake, combined with t= he orientation of the seismometer could be used to correct the est. of magnitude. Bob Barns = _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: Nick & Sophie Caporossi Subject: Homebrew Lehman Date: Wed, 09 Jul 97 17:24:57 -0500 -- [ From: Nick & Sophie Caporossi * EMC.Ver #2.5.02 ] -- Hi Charlie Thompson: You have a interesting Homepage. The jpgs of your homebrew seismometer give a pretty good idea of your setup. A few dimensions of your set up would be even more help. I would like to know the distance between the Copper Damper plate and the pickup coil. Do have any trouble keeping the Bolt end ( that is ground sharp) in place with the horizontal threaded rod? Some of the other sites on your Homepage are also interesting. Nick Caporossi nickcap@............. 40, 24.757N 74, 23.435W _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: "Walter Williams" Subject: GeoPhone? Date: Wed, 9 Jul 1997 16:08:01 +0000 Hello All, Ok. I am a rank newbie. I have read several of the archives for this year and I have clicked and clacked around the various PSN personal pages and now I have a question or two. What is a geophone?, and how is it useful for instrumenting seismic activity? I have seen several people's implementations of 'Lehman' seismometers and I was wondering if maybe an all digital (well almost) instrument is feasible? Some blend of optical/ccd and DSP without all the attendant analog filter circuits, maybe? Best Regards, Walt Williams, 97.07.09 SIS Woodland Hills, California, USA dfheli@.............. Checkout web page I helped make: http://mars.sgi.com/rovercom/rovcom.html _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: David A Nelson Subject: Re: Building a Rigid Seismometer Date: Thu, 10 Jul 1997 13:15:32 +1200 Ed, I agree totally, I sent Martin a personal message a few days ago also stating the resonance problems etc thanks for the professional backup Dave At 10:14 AM 7/9/97 -0600, you wrote: > >Content-Transfer-Encoding: 7bit > >Martin- > I think it is an EXTREMELY BAD idea to place the seismometer on any >kind of platform above the ground. The structure of the platform will >tend to produce amplifications and resonances that will significantly >compound the complexities that already exist from site response and >instrument response. So avoid it if you can. >-Edward > >Martin Brewer wrote: >> >> Hi everyone, >> >> Now that the Bermuda N-S, home-built Lehman instrument seems to be working, >> I am about to start building its E-W sibling. Being cramped for useable >> space, my idea is to build a tripod around the N-S instrument and place an >> E-W oriented sensor on a raised platform above the N-S instrument. >> >> I need some advice on the engineering so that the structure is rigid enough >> not to have unwanted resonance and can track 'quakes accurately. >> >> I am thinking of building a tripod about 4 feet high to support the base of >> the sensor. Can I use galvanized pipe (given that it will be built around >> the N-S ground level sensor)? Could I use concrete pillars? If so what >> diameter should they be? Can the pillars be reinforced by ordinary >> galvanized re-bar without affecting the N-S instrument which will have >> magnet and coil within, say, a foot of the nearest pillars? >> >> Does anyone have any working designs for instruments built four feet (plus >> or minus) above the ground? >> >> One last question. Does such an elevated support need to be bolted to the >> ground? From earlier correspondence on the PSN, I conclude that it is >> totally unnecessary. My "Doubting Thomas" of a brother-I- law (who is the >> nuts and bolts man on this project) thinks differently. >> >> I would be grateful for any and all comments. >> >> Regards, >> Martin >> >> _____________________________________________________________________ >> >> Public Seismic Network Mailing List (PSN-L) >> >> To leave this list email listserver@............. with the body of the >> message: leave PSN-L > >-- >Edward Cranswick Tel: 303-273-8609 >US Geological Survey, MS 966 Fax: 303-273-8600 >PO Box 25046, Federal Center cranswick@........ >Denver, CO 80225-0046 USA E.M. Forster said, "Only connect". > >_____________________________________________________________________ > >Public Seismic Network Mailing List (PSN-L) > >To leave this list email listserver@............. with the body of the >message: leave PSN-L > > Dave A. Nelson 24 Jensen St., Green Is., Dunedin, South Is.. New Zealand. http://psn.quake.net/dave/home.htm Q-BIT'SLAWNo.9: INTERCHANGEABLEPARTS-WON'TBE Q-BIT'SLAWNo.10: ANY WIRING ERRORINANYCONSTRUCTIONWILLBEIN THE DIRECTION OF THE MOST DAMAGE Q-BIT'SLAWNo.13:IDENTICALPARTSAREN'T _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: David A Nelson Subject: big event Date: Thu, 10 Jul 1997 13:24:53 +1200 Martin, you must have got a great record of the Ms6.8, Mw6.9 from nthrn coast of Venezuela "just down the road from you". the Univ. of Reno Helicorder shows a great trace ( www address near bottom of my quakes page) Dave Dave A. Nelson 24 Jensen St., Green Is., Dunedin, South Is.. New Zealand. http://psn.quake.net/dave/home.htm Q-BIT'SLAWNo.9: INTERCHANGEABLEPARTS-WON'TBE Q-BIT'SLAWNo.10: ANY WIRING ERRORINANYCONSTRUCTIONWILLBEIN THE DIRECTION OF THE MOST DAMAGE Q-BIT'SLAWNo.13:IDENTICALPARTSAREN'T _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: David A Nelson Subject: Re: GeoPhone? Date: Thu, 10 Jul 1997 13:33:54 +1200 hello Walt, welcome to the group, a geophone is a very small and compact seismometer they are designed for the exploration industry but work very well for general seismic recording see http://www.geospacecorp.com/lg11d.jpg for a pic. of one that I use here in New Zealand dave At 04:08 PM 7/9/97 +0000, you wrote: >Hello All, > >Ok. I am a rank newbie. > >I have read several of the archives for this year and I have clicked >and clacked around the various PSN personal pages and now I have >a question or two. > >What is a geophone?, and how is it useful for instrumenting seismic >activity? > >I have seen several people's implementations of 'Lehman' seismometers >and I was wondering if maybe an all digital (well almost) instrument >is feasible? Some blend of optical/ccd and DSP without all the >attendant analog filter circuits, maybe? > >Best Regards, > >Walt Williams, 97.07.09 >SIS >Woodland Hills, California, >USA >dfheli@.............. > >Checkout web page I helped make: >http://mars.sgi.com/rovercom/rovcom.html > >_____________________________________________________________________ > >Public Seismic Network Mailing List (PSN-L) > >To leave this list email listserver@............. with the body of the >message: leave PSN-L > > Dave A. Nelson 24 Jensen St., Green Is., Dunedin, South Is.. New Zealand. http://psn.quake.net/dave/home.htm Q-BIT'SLAWNo.9: INTERCHANGEABLEPARTS-WON'TBE Q-BIT'SLAWNo.10: ANY WIRING ERRORINANYCONSTRUCTIONWILLBEIN THE DIRECTION OF THE MOST DAMAGE Q-BIT'SLAWNo.13:IDENTICALPARTSAREN'T _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: "Martin Brewer" Subject: Re: big event Date: Wed, 9 Jul 1997 21:54:17 -0300 David A Nelson wrote > Subject: big event > Date: Wednesday, July 09, 1997 10:24 PM > > Martin, you must have got a great record of the Ms6.8, Mw6.9 from > nthrn coast of Venezuela "just down the road from you". I certainly did Dave. I am posting it to the PSN event address in case anyone would like to see it. The recorded amplitudes are ten times larger than the best recorded here so far. The focus being directly south of Bermuda the N-S Lehman is in optimal orientation to record the S waves. I think I shall have the trace colourised and framed :o) Regards, Martin _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: "Martin Brewer" Subject: Re: Building a Rigid Seismometer Date: Wed, 9 Jul 1997 22:19:12 -0300 > Edward Cranswick wrote > Subject: Re: Building a Rigid Seismometer >July 09, 1997 1:14 PM > > Martin- > I think it is an EXTREMELY BAD idea to place the seismometer on any > kind of platform above the ground. Edward, Thank you for your advice. As you know Dave Nelson also pointed out the resonance problems. As a result of your's and David's comments, I think it is likely that I shall either find a convenient space in the basement (given the potential problems, more spaces are appearing convenient all the time!) or build a concrete slab outside. I have one of Larry's three-channel filter/amplifier boards as I had always intended to build a three axis system. The problem, as I understand it, is that I cannot afford to have more than about six feet of phono cable between the pickup coil and the amplifier. Am I right? or can I get away with say 12 feet? Of course I could buy another filter/amp board from Larry but I would rather not have to spend more than necessary :o) regards, Martin _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: "Martin Brewer" Subject: Re: Surface Waves Date: Wed, 9 Jul 1997 22:31:57 -0300 Martin, I looked in my DSR files for 7/4-7/8 (today at 18:00 UTC) and see nothing around 1:30 for any of these days. I checked them all since you did not state a date. Bob Barns Sorry Bob, The trace came through on 8 June, minutes before I e-mailed you. I must learn to be more explicit. What sort of recording did you get for today's Venezuela event [19:24 UTC, 9 July 1997, Lat 10.43N, Long 63.49W, Mag 6.8 - USGS NEIC data]? Regards, Martin _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: "Martin Brewer" Subject: Re: Homebrew Lehman Date: Wed, 9 Jul 1997 22:49:32 -0300 ---------- > Nick & Sophie Caporossi wrote about > Homebrew Lehman > Date: Wednesday, July 09, 1997 7:24 PM to > Charlie Thompson: > > Do have any trouble keeping the Bolt end ( that is ground sharp) in place > with the horizontal threaded rod? I had the same question when I started to build my Lehman. What I did was to find the balance point of the boom assembly - with all weights, magnet and damping mechanism in place - when it was suspended vertically from it's suspension wire. When the support wire is attached to the boom (via a washer with a small hole drilled near its edge) at the balance point determined by test hanging it as described, there is no tendency for the knife-edge at the other end of the boom to slip down or up from its position against the support system. I achieved this balance by splitting the weight. I have two three pound lead weights. One of them is on the knife-edge side of the magnet and its counterbalancing weight, the other is on the other side. I think on my next attempt I shall reduce the weight of the distant boom weight so that I can move it closer to the inner weight. On my assembly the weights are about 8 inches apart. I worry that some arcane compound pendulum effect may produce unwanted resonance. Comments greatly appreciated. regards, Martin _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: David A Nelson Subject: Venezuela quake Date: Thu, 10 Jul 1997 19:57:21 +1200 Martin, what an excellent record WELL DONE Dave Dave A. Nelson 24 Jensen St., Green Is., Dunedin, South Is.. New Zealand. http://psn.quake.net/dave/home.htm Q-BIT'SLAWNo.9: INTERCHANGEABLEPARTS-WON'TBE Q-BIT'SLAWNo.10: ANY WIRING ERRORINANYCONSTRUCTIONWILLBEIN THE DIRECTION OF THE MOST DAMAGE Q-BIT'SLAWNo.13:IDENTICALPARTSAREN'T _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: Larry Cochrane Subject: Re: GeoPhone? Date: Thu, 10 Jul 1997 00:42:33 -0700 At 01:33 PM 7/10/97 +1200, David Nelson wrote: >hello Walt, > welcome to the group, a geophone is a very small and >compact seismometer they are designed for the exploration industry but work >very well for general seismic recording > I'm not sure about that... Short period sensors, like geophones, are fine for local and larger regional events but are not good for teleseismic events. Short period velocity sensors just can't pickup, or resolve, the low frequency waves from distant events. I think a Lehman (or modified SG sensors), is a little more "general purpose" do to its broader frequency range. A Lehman, with a period over 10 seconds, can be used for both local and teleseismic events. The SG sensor (see http://psn.quake.net/sgsensor.html) design can be modified to recording local events better by taking a signal out of the sensors before the integrator. This creates a signal that has more high frequency information and is better for viewing local events. Since Walt lives in So. California he can us a geophone and receive lots of events, but someone not so "lucky" to live in an EQ area will need something like a Lehman or SG sensors to pickup teleseismic events. Just my .02 cents... -Larry Cochrane Redwood City, PSN _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: Larry Cochrane Subject: Re: Building a Rigid Seismometer Date: Thu, 10 Jul 1997 00:57:19 -0700 At 10:19 PM 7/9/97 -0300, Martin Brewer wrote: >Edward, >Thank you for your advice. As you know Dave Nelson also pointed out the >resonance problems. As a result of your's and David's comments, I think it >is likely that I shall either find a convenient space in the basement >(given the potential problems, more spaces are appearing convenient all the >time!) or build a concrete slab outside. I have one of Larry's >three-channel filter/amplifier boards as I had always intended to build a >three axis system. The problem, as I understand it, is that I cannot afford >to have more than about six feet of phono cable between the pickup coil >and the amplifier. Am I right? or can I get away with say 12 feet? Of >course I could buy another filter/amp board from Larry but I would rather >not have to spend more than necessary :o) >regards, The problem is your are dealing with low levels of signal and the high impedance of the pickup coil. 12 to 15 feet of good shielded audio or RF cable should be fine. The thing to do is try it and see how much extra noise you get with the added cable. What you can do is see how much background noise (Min/Max A/D counts) you get with the pickup coil connected to the amp card with a small amount of cable. Then add the extra cable and see if the noise goes up much. This test should be done without the coil near a magnet. Hope this helps. Larry Cochrane Redwood City, PSN _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: "Martin Brewer" Subject: Re: Building a Rigid Seismometer Date: Thu, 10 Jul 1997 06:49:21 -0300 ---------- > From: Larry Cochrane > > The problem is your are dealing with low levels of signal and the high > impedance of the pickup coil. 12 to 15 feet of good shielded audio or RF > cable should be fine. The thing to do is try it and see how much extra > noise you get with the added cable. What you can do is see how much > background noise (Min/Max A/D counts) you get with the pickup coil > connected to the amp card with a small amount of cable. Then add the extra > cable and see if the noise goes up much. This test should be done without > the coil near a magnet. Thank you Larry for your good advice. I shall experiment as you suggest. Martin _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: "Martin Brewer" Subject: Re: Venezuela quake Date: Thu, 10 Jul 1997 06:54:53 -0300 ---------- > From: David A Nelson > To: psn-l@............. > Subject: Venezuela quake > Date: Thursday, July 10, 1997 4:57 AM > > Martin, > what an excellent record WELL DONE > > Dave > Dave A. Nelson Thank you Dave, I'm still a bit awestruck that a home made device like mine can do such a good job. Of course it would be nothing without Larry's excellent electronics. Even so it is very pleasing. Martin _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: Robert L Barns <75612.2635@..............> Subject: Re: Homebrew Lehman Date: Thu, 10 Jul 1997 10:48:30 -0400 Martin, The common use for a Lehman is for teleseismic events. This means that= frequencies less than 0.1 Hz are the only ones of primary concern. I thi= nk that it is impossible to get boom or suspension resonances at these low frequencies even if you tried. Bob Barns _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: Robert L Barns <75612.2635@..............> Subject: Re: Surface Waves Date: Thu, 10 Jul 1997 10:48:26 -0400 Martin, Venezuela emitted a beauty! Should we send a thank-you note? Probably= not--I doubt that the government caused it. I got 20,000 counts p-p, 112,000 nm/sec with a signal/noise ratio of 100. P, S & SS obvious. With my P & S pics, I got org. of 19:24:31 and dis= t. 2154 mi. My clock was 2" fast. I wonder where the other 18 secs. went. I also saw what may be 2 aftershocks. One near 21:55:35 (1400 counts p-p) and one near 24:4:32 (700 counts). The tail of the main 19:24:11 shock was still vis. but these were above the level of the tail. Take a look for these. Bob Barns _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: Doug Crice Subject: Re: Surface Waves Date: Thu, 10 Jul 1997 08:31:21 -0700 The morning news mentioned that a massive rescue effort is underway in Venezuela. A multi-story building collapsed and they reported 40 are believed dead. As with all earthquake reports from under-developed countries, the casualty count will probably increase as more news filters out. There were no pictures in the report, and the story was followed immediately with pictures from Mars. I was struck by the fact that we could get pictures from Mars but not from Venezuela. Doug Crice _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: JIM CRISTIANO Subject: Re: cables Date: Thu, 10 Jul 1997 09:13:09 -0700 Larry Cochrane wrote: > The problem is your are dealing with low levels of signal and the high > impedance of the pickup coil. 12 to 15 feet of good shielded audio or RF > cable should be fine. The thing to do is try it and see how much extra > noise you get with the added cable. What you can do is see how much > background noise (Min/Max A/D counts) you get with the pickup coil > connected to the amp card with a small amount of cable. Then add the extra > cable and see if the noise goes up much. This test should be done without > the coil near a magnet. > > Hope this helps. > et al, This is a good case for the afore mentioned suggestions of using a differential input amplifier configuration on the coil input and a 4-20mA current loop for the output. A current to voltage converter ( easier than it sounds) would interface to the A to D. Burr-Brown has a hot new 4-20mA IC called a XTR105 along with other current transmitter IC'S at burr-brown.com. If you're going remote, Linx tech. in Medford, Or. sells very small single-in-line package data radio transmitters and receiver boards that work at up to 800'. I found a way to get a linear, high sensitivity output from a 25mV/gauss MicroSwitch Linear Hall Effect Device. The problem is that the output is dc and getting the #*$?@~! magnet centered to the LOHET face for zero is impossible. So now I'm trying to use it in a vertical force-balanced sensor so that it will auto-zero itself. Regards, Jim cristiano@........... _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: Dennis Leatart Subject: VENEZUELA QUAKE Date: Thu, 10 Jul 1997 12:25:10 -0700 I also got a good trace of the Venezuela event-- 3 hours of data and over 56,000 data points. I also am seeing what looks like some aftershocks and surface waves. I have this on a *.bmp file if anyone is interested, I'll send you a copy? -- _____ __ | \.-----.-----.-----.|__|.-----. | -- | -__| | || ||__ --| |_____/|_____|__|__|__|__||__||_____| _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: "Walter Williams" Subject: Seismic Abstract Date: Thu, 10 Jul 1997 16:10:14 +0000 Hello All, In my studies I ran across this interesting abstract which may be of interest to some of you, please reference: http://www.agu.org/pubs/abs/jb/96JB01905/96JB01905.html Cheers, Walt Williams, 97.07.10 Woodland Hills, California, USA dfheli@.............. _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: "Martin Brewer" Subject: Re: Homebrew Lehman Date: Thu, 10 Jul 1997 19:09:55 -0300 From: Robert L Barns Subject: Re: Homebrew Lehman Date: Thursday, July 10, 1997 11:48 AM Martin, The common use for a Lehman is for teleseismic events. This means that frequencies less than 0.1 Hz are the only ones of primary concern. I think that it is impossible to get boom or suspension resonances at these low frequencies even if you tried. Bob Barns Hi Bob, Thanks for the comforting words. But I'd seem to have seen some relatively high frequency stuff at about 0.3Hz in some events which I took to be P wave arrivals. Am I wrong? Regards, Martin _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: "Rex Klopfenstein, Jr." Subject: Re: Transmitting signal Date: Thu, 10 Jul 1997 19:22:16 -0400 ---------- > From: Martin Brewer > To: PSN-L Mailing List > Subject: Re: Building a Rigid Seismometer > Date: Wednesday, July 09, 1997 9:19 PM > > > The problem, as I understand it, is that I cannot afford > to have more than about six feet of phono cable between the pickup coil > and the amplifier. Am I right? or can I get away with say 12 feet? You might look at using 4-20mA current loops. There are ic's manufactured by Burr-Brown and others that convert voltage signals into 4-20mA tracking current loops. There are also ic's that convert the 4-20mA back to voltage _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: "Martin Brewer" Subject: Re: Surface Waves Date: Thu, 10 Jul 1997 19:29:34 -0300 From: Robert L Barns Subject: Re: Surface Waves Date: Thursday, July 10, 1997 11:48 AM Martin, Venezuela emitted a beauty! Hi Bob, She sure did. I didn't know seismic waves got that big!! I've been looking for anything that pokes it's head out of the 'ground noise. Obviously I have to set my sights higher. On that note, I have thought that I have been seeing some rumblings from the Montserrat volcano. have you been recording any long duration twice background microseismic activity of late especially on 25 June? With my P & S pics, I got org. of 19:24:31 and dist. 2154 mi. My clock was 2" fast. I wonder where the other 18 secs. went. Well two seconds of that is probably from my clock which could have been as much as 2 seconds slow. My origin time of 19:24:23 is still is still 12 seconds ahead of USGS's origin time of 09:24:11. I note on my trace that, depending on the Y-scale being used, the P wave pick can change. Two seconds before the main - relatively constant amplitude - P arrivals, there is a short train of lower amplitude waves that are still well above background. You may want to have a look at the initial P wave train at higher "magnification" I also saw what may be 2 aftershocks. One near 21:55:35 (1400 counts p-p) and one near 24:4:32 (700 counts). The tail of the main 19:24:11 shock was still vis. but these were above the level of the tail. Take a look for these. Bob Barns I looked for the reported aftershock of Mag 4.4 that USGS reported at 20:06 but of course that was completely swamped. I shall have look and see if I can see the aftershocks you indicate. Thanks for the challenge :o) Regards, Martin _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: "Martin Brewer" Subject: Re: Transmitting signal Date: Thu, 10 Jul 1997 19:48:11 -0300 ---------- > From: Rex Klopfenstein, Jr. > Subject: Re: Transmitting signal > Date: Thursday, July 10, 1997 8:22 PM > > > > ---------- > > From: Martin Brewer > > To: PSN-L Mailing List > > Subject: Re: Building a Rigid Seismometer > > Date: Wednesday, July 09, 1997 9:19 PM > > > > > > The problem, as I understand it, is that I cannot afford > > to have more than about six feet of phono cable between the pickup coil > > and the amplifier. Am I right? or can I get away with say 12 feet? > > You might look at using 4-20mA current loops. There are ic's manufactured > by Burr-Brown and others that convert voltage signals into 4-20mA tracking > current loops. There are also ic's that convert the 4-20mA back to voltage > Hi Rex, Thank you for your suggestion. I might have to set the second sensor in a more remote location than I would like to, in which case I might want to learn more about the solution you suggest. I am relatively ignorant in this area and will need some help if it gets to that stage. Regards, Martin _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: "Walter Williams" Subject: Meteor & Seismic Detectors Date: Thu, 10 Jul 1997 17:08:06 +0000 Hello All, I stumbled onto this "seismic instrument" while doing my search for low frequency anomaly detectors. Probably a very simple instrument? See: http://www.nitehawk.com/rasmit/jml0.html "EARTHQUAKE GROUND VELOCITY SENSOR Radio Astronomy Supplies is pleased to offer the FRANKLIN Ground Velocity Sensor. This system is the first portable and user friendly instrument ever produced, for recording earthquake and ground motion signals. You can record and view signals hundreds of times smaller than can be felt! This plug and go system simply attaches to your computer's serial port. Windows or DOS software included (please specify). " Cheers, Walt Williams, 97.07.10 Woodland Hills, California, USA dfheli@.............. _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: David A Nelson Subject: Re: venezuela Date: Fri, 11 Jul 1997 12:40:16 +1200 Doug, the pic from venezuela show major damage...... so far 56 confirmed dead more expexted hospitals flooded with casulties people calling , from within the rubble, to rescuers using cellphones. Dave At 08:31 AM 7/10/97 -0700, you wrote: >The morning news mentioned that a massive rescue effort is underway in >Venezuela. A multi-story building collapsed and they reported 40 are >believed dead. As with all earthquake reports from under-developed >countries, the casualty count will probably increase as more news >filters out. > >There were no pictures in the report, and the story was followed >immediately with pictures from Mars. I was struck by the fact that we >could get pictures from Mars but not from Venezuela. > >Doug Crice > > > >_____________________________________________________________________ > >Public Seismic Network Mailing List (PSN-L) > >To leave this list email listserver@............. with the body of the >message: leave PSN-L > > Dave A. Nelson 24 Jensen St., Green Is., Dunedin, South Is.. New Zealand. http://psn.quake.net/dave/home.htm Q-BIT'SLAWNo.9: INTERCHANGEABLEPARTS-WON'TBE Q-BIT'SLAWNo.10: ANY WIRING ERRORINANYCONSTRUCTIONWILLBEIN THE DIRECTION OF THE MOST DAMAGE Q-BIT'SLAWNo.13:IDENTICALPARTSAREN'T _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: David A Nelson Subject: Re: cables Date: Fri, 11 Jul 1997 12:54:22 +1200 all, on one of my sensors I am using 30 metres (~100ft) of RG59 (75 Ohm) coax cable between the seismometer and the pre-amp (that I use) the non seismic noise is virtually unmeasureable. the two seismometers that are on the digital system are fed to the preamps with a 10 metre (~30 ft) of twin core screened computer data cable and again the unwanted noise level is unmeasurable obviously pre-amp input arrangement may be a factor I am planning to try one of Larry C's pre-amps to see the difference between it and the three I currently use Dave N. At 09:13 AM 7/10/97 -0700, you wrote: >Larry Cochrane wrote: > >> The problem is your are dealing with low levels of signal and the high >> impedance of the pickup coil. 12 to 15 feet of good shielded audio or RF >> cable should be fine. The thing to do is try it and see how much extra >> noise you get with the added cable. What you can do is see how much >> background noise (Min/Max A/D counts) you get with the pickup coil >> connected to the amp card with a small amount of cable. Then add the extra >> cable and see if the noise goes up much. This test should be done without >> the coil near a magnet. >> >> Hope this helps. >> > et al, > This is a good case for the afore mentioned suggestions of > using a differential input amplifier configuration on the coil > input and a 4-20mA current loop for the output. A current to > voltage converter ( easier than it sounds) would interface to > the A to D. > > Burr-Brown has a hot new 4-20mA IC called a XTR105 along with > other current transmitter IC'S at burr-brown.com. > > If you're going remote, Linx tech. in Medford, Or. sells > very small single-in-line package data radio transmitters and > receiver boards that work at up to 800'. > > I found a way to get a linear, high sensitivity output from > a 25mV/gauss MicroSwitch Linear Hall Effect Device. The problem > is that the output is dc and getting the #*$?@~! magnet centered > to the LOHET face for zero is impossible. So now I'm trying > to use it in a vertical force-balanced sensor so that it will > auto-zero itself. > > Regards, > > Jim cristiano@........... > > >_____________________________________________________________________ > >Public Seismic Network Mailing List (PSN-L) > >To leave this list email listserver@............. with the body of the >message: leave PSN-L > > Dave A. Nelson 24 Jensen St., Green Is., Dunedin, South Is.. New Zealand. http://psn.quake.net/dave/home.htm Q-BIT'SLAWNo.9: INTERCHANGEABLEPARTS-WON'TBE Q-BIT'SLAWNo.10: ANY WIRING ERRORINANYCONSTRUCTIONWILLBEIN THE DIRECTION OF THE MOST DAMAGE Q-BIT'SLAWNo.13:IDENTICALPARTSAREN'T _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: Edward Cranswick Subject: Re: Venezuela quake Date: Thu, 10 Jul 1997 21:54:55 -0600 Martin- That is a very beautiful set of wiggles you recorded from Venezuela. It took me a little while to get my act together to look at them, but I am very impressed. -Edward -- Edward Cranswick Tel: 303-273-8609 US Geological Survey, MS 966 Fax: 303-273-8600 PO Box 25046, Federal Center cranswick@........ Denver, CO 80225-0046 USA E.M. Forster said, "Only connect". _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: Al Allworth Subject: Re: Transmitting signal Date: Thu, 10 Jul 1997 23:40:19 -0700 At 07:48 PM 7/10/97 -0300, you wrote: > >Thank you for your suggestion. I might have to set the second sensor in a >more remote location than I would like to, in which case I might want to >learn more about the solution you suggest. I am relatively ignorant in >this area and will need some help if it gets to that stage. Another suggestion: Since an op-amp input is often used, just put the input resistor at the remote site, use a good low noise cable, and connect the cable directly to the neg. input of the op amp. Sometimes a small portion of the input resistance needs to be at the op-amp. I have used this system successfully in other applications. It should work for this as well. The ground shield needs to be well connected at both ends. ____________________________________________________________________________ Al Allworth, Gold Beach, OR aallworth@........ _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: John Hernlund Subject: Re: GeoPhone? Date: Fri, 11 Jul 1997 00:01:24 -0700 (MST) On Thu, 10 Jul 1997, Larry Cochrane wrote: > I'm not sure about that... Short period sensors, like geophones, are fine > for local and larger regional events but are not good for teleseismic > events. Short period velocity sensors just can't pickup, or resolve, the > low frequency waves from distant events. I think a Lehman (or modified SG > sensors), is a little more "general purpose" do to its broader frequency > range. A Lehman, with a period over 10 seconds, can be used for both local > and teleseismic events. > > The SG sensor (see http://psn.quake.net/sgsensor.html) design can be > modified to recording local events better by taking a signal out of the > sensors before the integrator. This creates a signal that has more high > frequency information and is better for viewing local events. I think it is interesting that such a basic design like the Lehman can be so useful. I have been thinking about some day building a small array of them. Each would respond well to different frequencies simply by altering the angle and/or length of the boom. Has anyone here ever tried this? ****************************************************************************** John Hernlund E-mail: hernlund@....... WWW: http://www.mc.maricopa.edu/academic/phy_sci/Geology/hernlund/ ****************************************************************************** _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: Edward Cranswick Subject: Re: GeoPhone? Date: Fri, 11 Jul 1997 09:03:28 -0600 Content-Transfer-Encoding: 7bit John- The Soviets builts a strong motion instrument that consisted of several different pendulums with diiferent natural frequencies. This device constituted, in effect, a coarse analog spectrum analyzer. However, by digitally recording a "broad-band" sensor, one can obtain the same information by digitally narrow-band filtering the broad-band signal at different frequencies, e.g., this can be done with Larry's WinQuake. -Edward John Hernlund wrote: > > On Thu, 10 Jul 1997, Larry Cochrane wrote: > > I'm not sure about that... Short period sensors, like geophones, are fine > > for local and larger regional events but are not good for teleseismic > > events. Short period velocity sensors just can't pickup, or resolve, the > > low frequency waves from distant events. I think a Lehman (or modified SG > > sensors), is a little more "general purpose" do to its broader frequency > > range. A Lehman, with a period over 10 seconds, can be used for both local > > and teleseismic events. > > > > The SG sensor (see http://psn.quake.net/sgsensor.html) design can be > > modified to recording local events better by taking a signal out of the > > sensors before the integrator. This creates a signal that has more high > > frequency information and is better for viewing local events. > > I think it is interesting that such a basic design like the Lehman can > be so useful. I have been thinking about some day building a small array > of them. Each would respond well to different frequencies simply by > altering the angle and/or length of the boom. Has anyone here ever tried > this? > > ****************************************************************************** > > John Hernlund > E-mail: hernlund@....... > WWW: http://www.mc.maricopa.edu/academic/phy_sci/Geology/hernlund/ > > ****************************************************************************** > > _____________________________________________________________________ > > Public Seismic Network Mailing List (PSN-L) > > To leave this list email listserver@............. with the body of the > message: leave PSN-L -- Edward Cranswick Tel: 303-273-8609 US Geological Survey, MS 966 Fax: 303-273-8600 PO Box 25046, Federal Center cranswick@........ Denver, CO 80225-0046 USA E.M. Forster said, "Only connect". _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: Floyd Schad Subject: Re: GeoPhone? Date: Fri, 11 Jul 1997 08:38:05 -0700 Edward Cranswick wrote: > > Content-Transfer-Encoding: 7bit > > John- > The Soviets builts a strong motion instrument that consisted of several > different pendulums with diiferent natural frequencies. This device > constituted, in effect, a coarse analog spectrum analyzer. However, by > digitally recording a "broad-band" sensor, one can obtain the same > information by digitally narrow-band filtering the broad-band signal at > different frequencies, e.g., this can be done with Larry's WinQuake. > -Edward > > John Hernlund wrote: > > > > On Thu, 10 Jul 1997, Larry Cochrane wrote: > > > I'm not sure about that... Short period sensors, like geophones, are fine > > > for local and larger regional events but are not good for teleseismic > > > events. Short period velocity sensors just can't pickup, or resolve, the > > > low frequency waves from distant events. I think a Lehman (or modified SG > > > sensors), is a little more "general purpose" do to its broader frequency > > > range. A Lehman, with a period over 10 seconds, can be used for both local > > > and teleseismic events. > > > > > > The SG sensor (see http://psn.quake.net/sgsensor.html) design can be > > > modified to recording local events better by taking a signal out of the > > > sensors before the integrator. This creates a signal that has more high > > > frequency information and is better for viewing local events. > > > > I think it is interesting that such a basic design like the Lehman can > > be so useful. I have been thinking about some day building a small array > > of them. Each would respond well to different frequencies simply by > > altering the angle and/or length of the boom. Has anyone here ever tried > > this? > > > > ****************************************************************************** > > > > John Hernlund > > E-mail: hernlund@....... > > WWW: http://www.mc.maricopa.edu/academic/phy_sci/Geology/hernlund/ > > > > ****************************************************************************** > > > > _____________________________________________________________________ > > > > Public Seismic Network Mailing List (PSN-L) > > > > To leave this list email listserver@............. with the body of the > > message: leave PSN-L > > -- > Edward Cranswick Tel: 303-273-8609 > US Geological Survey, MS 966 Fax: 303-273-8600 > PO Box 25046, Federal Center cranswick@........ > Denver, CO 80225-0046 USA E.M. Forster said, "Only connect". > > _____________________________________________________________________ > > Public Seismic Network Mailing List (PSN-L) > > To leave this list email listserver@............. with the body of the > message: leave PSN-L _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: Robert L Barns <75612.2635@..............> Subject: Re: Homebrew Lehman Date: Fri, 11 Jul 1997 15:13:58 -0400 Martin, No, you are right. The P & S will have somewhat higher freq. components--prob. up to 1 Hz. or so but even at these freqs., I would not= expect any unwanted resonances. Bob Barns _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: John Hernlund Subject: Re: GeoPhone? Date: Fri, 11 Jul 1997 15:10:17 -0700 (MST) On Fri, 11 Jul 1997, Edward Cranswick wrote: > Content-Transfer-Encoding: 7bit > > John- > The Soviets builts a strong motion instrument that consisted of several > different pendulums with diiferent natural frequencies. This device > constituted, in effect, a coarse analog spectrum analyzer. However, by > digitally recording a "broad-band" sensor, one can obtain the same > information by digitally narrow-band filtering the broad-band signal at > different frequencies, e.g., this can be done with Larry's WinQuake. > -Edward Yes, I already use this method, but fancy analysis cannot always correct for the inefficiencies of the physical device, especially if it does not respond at all to some frequencies... ****************************************************************************** John Hernlund E-mail: hernlund@....... WWW: http://www.mc.maricopa.edu/academic/phy_sci/Geology/hernlund/ ****************************************************************************** _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: "Martin Brewer" Subject: Re: Venezuela quake Date: Fri, 11 Jul 1997 21:24:37 -0300 > From: Edward Cranswick > Subject: Re: Venezuela quake > Date: Friday, July 11, 1997 12:54 AM > > Martin- > That is a very beautiful set of wiggles you recorded from Venezuela. > It took me a little while to get my act together to look at them, but I > am very impressed. > -Edward > Edward, Thank you for your kind comments. I can't believe how well this all works. Regards, Martin _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: "Martin Brewer" Subject: Re: Transmitting signal Date: Fri, 11 Jul 1997 21:31:15 -0300 ---------- > From: Al Allworth > Subject: Re: Transmitting signal > Date: Friday, July 11, 1997 3:40 AM > > At 07:48 PM 7/10/97 -0300, you wrote: > > > > >Thank you for your suggestion. I might have to set the second sensor in a > >more remote location than I would like to, in which case I might want to > >learn more about the solution you suggest. I am relatively ignorant in > >this area and will need some help if it gets to that stage. > > Another suggestion: > Since an op-amp input is often used, just put the input resistor at the > remote site, use a good low noise cable, and connect the cable directly to > the neg. input of the op amp. Sometimes a small portion of the input > resistance needs to be at the op-amp. I have used this system successfully > in other applications. It should work for this as well. The ground shield > needs to be well connected at both ends. > ____________________________________________________________________________ > > Al Allworth, Gold Beach, OR aallworth@........ Al, Thank you for your suggestion. There seems to be many ways to skin this cat. When I get that far down the road and need help with the details, I shall undoubtedly have to pick your brains and those of everyone else who has contributed to solving my problem. Thanks everyone. Regards, Martin _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: "Martin Brewer" Subject: Re: Homebrew Lehman Date: Fri, 11 Jul 1997 21:51:13 -0300 ---------- From: Robert L Barns <75612.2635@..............> Subject: Re: Homebrew Lehman Date: Friday, July 11, 1997 4:13 PM Martin, No, you are right. The P & S will have somewhat higher freq. components--prob. up to 1 Hz. or so but even at these freqs., I would not expect any unwanted resonances. Bob Barns Hi Bob, I shall keep your comments in mind as I go forward with .BER E-W. I am picking up background of micro-seismic activity with much increased amplitude (doubled) as Tropical Storm Bill passes within 150 miles or so. Unexpectedly (for me), the period of the waves has only increased slightly from about 3.7 to about 4.1. I would have expected a much greater increase in period. Perhaps there is some kind of integration effect in the water/bedrock system that keeps the general microseismic activity fairly constant. Are you seeing any effects there in New Jersey from T.S. Bill? Regards, Martin _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: frankcnd@.......... (Frank Condon) Subject: Animals are Strange! Date: xMessageSize=2000000 Hello all: I thought that I'd report this information obtained from a friend in the NW San Bernardino, CA area: This is in the same area where a 4.2 temblor struck about two weeks ago. The people who live in the area say that their pets are acting very strange! This includes both dogs and cats. I don't know if this means anything... But, I still wanted to be able to report it before something did happen again. I have an interest in watching animals myself and have witness bizarre behavior in equestrians on two ocassions before earthquakes and once with canines. Best regards, Frank Condon "In the High Desert of California" Email to: "frankcnd@.........." _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: frankcnd@.......... (Frank Condon) Subject: San Bernardino, CA Earthquake Swarm! Date: xMessageSize=2000000 Hi all: Well, I wasn't sure if anything would come out of the prediction made on July 11, 1997. Once again, animals have shown us that they are indeed another method of seismic prediction! On July 12, 1997; a swarm of earthquakes ( aftershocks) were observed in the area of the prediction. This is in the area 3-4 miles NW of the city closest to the epicenter of the 4.2 that occurred two weeks ago yesterday. This is the largest of the swarm that was observed according to information from the CALTECH finger server: ============================================================================= DATE UTC LAT. LON. DEPTH MAG. Q COMMENT yy-mm-dd hh:mm:ss (deg.) (deg.) (km) typ -------- -------- -------------- ------ ------ - ---------------------------- 97/07/12 18:05:40 34.15N 117.34W 9.4 3.6MLG A 4mi. NW of SAN BERNARDINO I'd say "people should keep an eye on those pets!" Especially, if they're in an area prone to earthquakes. If you see anything odd, or can add to this observation, then I'd appreciate hearing from you! Thanks, Frank Condon "In the High Desert of So. California" Email to: "frankcnd@.........." _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L) From: David A Nelson Subject: Re: Meteor & Seismic Detectors Date: Mon, 14 Jul 1997 00:13:35 +1200 Walt, this is very expensive, Larry Cochrane's SDR logging system and Winquake software is ~ half the price and you have data compatability with many othersin the PSN group Dave At 05:08 PM 7/10/97 +0000, you wrote: >Hello All, > >I stumbled onto this "seismic instrument" while doing my search for >low frequency anomaly detectors. Probably a very simple instrument? > >See: >http://www.nitehawk.com/rasmit/jml0.html > >"EARTHQUAKE GROUND VELOCITY SENSOR > >Radio Astronomy Supplies is pleased to offer the FRANKLIN Ground >Velocity Sensor. This system is the first portable and user friendly >instrument ever produced, for recording earthquake and ground motion >signals. You can record and view signals hundreds of times smaller >than can be felt! This plug and go system simply attaches to your >computer's serial port. Windows or DOS software included (please >specify). " > > >Cheers, > >Walt Williams, 97.07.10 >Woodland Hills, California, >USA >dfheli@.............. > > > > >_____________________________________________________________________ > >Public Seismic Network Mailing List (PSN-L) > >To leave this list email listserver@............. with the body of the >message: leave PSN-L > > Dave A. Nelson 24 Jensen St., Green Is., Dunedin, South Is.. New Zealand. http://psn.quake.net/dave/home.htm IF there indeed other parallel universes... I can now rest in the knowledge, that in at least one of them, I am filthy rich and drive a red Ferrari _____________________________________________________________________ Public Seismic Network Mailing List (PSN-L)