PSN-L Email List Message
Subject: Re[2]: unusual frequency
From: Angel sismos@..............
Date: Fri, 7 Nov 2008 10:49:23 +0000
Hello Bob,
The diminished S wave might be a source mechanism thing. The P and S radiated energy is lobed, not circular and uniform. Some station might be in the azimuth between the radiation lobes of the S. Some directions see an S and other don't. Deep event also tend to have diminished S waves.
angel
Sunday, November 2, 2008, 11:17:21 PM, you wrote:
> Without knowing the epicenter of the event, you cannot draw too many
> conclusions. I downloaded the event using VASE, and look at it with
> SAC. I used the unfiltered raw data from the IU/TUC station (STS-1)
> and believe the P wave arrival time is 13:36:20 for that station. I
> can pick out the Love & Rayleigh waves. However, the S wave is of
> very low amplitude. I observed one very low amplitude oscillation
> that could correspond to an S wave about 13:37:25, for a S-P time of
> 65 seconds or 4.47 degrees ( 496.75 km). In addition, the rayleigh
> waves are much more pronounced on the vertical and north channels
> which would be consistent with an event that is more southerly from
> the receiving station than southwest. The Love waves first appear
> about 13:37:45, and the Rayleigh waves appear about 13:38:25. Without
> more information, it is not really possible to draw any conclusions on
> why there was a diminished S wave. I have not looked at the event
> with other than my station and Tucson. To me, it looks like a normal
> regional event, but with a magnitude of less than 4.0, most likely
> south of the border in Mexico.
> Keep in mind one big problem in analyzing regional events is there is
> insufficient time for good wave separation. They are all together and
> that can complicate trying to pick out individual waves.
> Bob Hancock
> On Nov 2, 2008, at 2:11 AM, Geoff wrote:
>> Hello Bob;
>> me Not being a physics major or math person.
>> Thats Interesting since I had a s-p or s-L time
>> of 2 minutes and that translates to
>> 600 + miles maybe 700. This event set off
>> my automatic recording which usually does
>> not happen unless the quake is about 4.0
>> at 400 miles. For some reason more energy then
>> expected has arrived at this station sort of like
>> what bubbleheads ( submarine sailors )
>> might call a convergence zone
>> which happens in the ocean with sound waves.
>> Maybe quake waves in the earth behave like
>> sound waves in the ocean and are lazy which
>> will focus the energy at discreet distances
>> from the event. By lazy I mean they seem
>> to bend ( refract ) to the slowest velocity hitting the surface
>> with concentrated focused energy
>> in concentric rings around the event out to
>> some distance. Such behavior requires enough
>> depth of the strata to allow for this bending to happen.
>> Does this mean possibly deep crust or from the mantel ?
>> I should imagine the moho would keep a CZ zone
>> from the crust because it would reflect at that point
>> and divide the energy instead of refracting it.
>> What do you think might be going on that
>> would concentrate the energy from a less than
>> usual quake to set off my recording alarm ?
>> I understand wave velocity changes is the best way
>> to guess how waves are effected as they propagate.
>> Any sudden change is like a mirror and a gradual
>> change is like a lens.
>> I understand a transmitted ( radio wave ) signal can be bent
>> by having a series of antennas with a phasing
>> slightly later from antenna to antenna so that
>> the delaying of the phases of a single wave
>> will make the antenna behave as a massive
>> variable lens thus the phased array kind of antenna
>> or wullenwebber array.
>> Since we can not do what mother nature has
>> not already done in one way or another I can
>> imagine the earth itself is somehow making
>> areas of more and less energy as energy spreads
>> away from the focal point. I must have been
>> in an increased energy point if the quake
>> was less than 4.0 and 600 miles away.
>> Regards;
>> geoff
>> ----- Original Message ----- From: "Bob Hancock"
>>
>> To:
>> Sent: Saturday, November 01, 2008 8:16 PM
>> Subject: Re: unusual frequency
>>> This event appears to be consistent with other low magnitude
>>> events that have occurred to the Southwest of Tucson, AZ. I have
>>> seen other events that are similar, and no information was ever
>>> posted on them. I noticed the event was visible across the lower
>>> 48 states, and southern Alaska. It is most likely less than M 4.0
>>> as that is the USGS minimum cutoff for display of information on
>>> international events.
>>> Bob Hancock
>>> On Nov 1, 2008, at 2:53 PM, Geoff wrote:
>>>> Hello Mr. Thomas Dick;
>>>> My Sensor located very close to 33.42138N -111.57477W about
>>>> 507Meters above mean sea level.
>>>> I saw that TUC near Tucson also saw this signal about 1336 to
>>>> 1338 on 31OCT2008 UTC.
>>>> I have not analyzed it to get an accurate and precise time simply
>>>> because I can not
>>>> tell for sure it is in fact an Earthquake. If no one else is
>>>> reporting it I do not trust
>>>> what I am looking at. In order for me to properly read a signal
>>>> it takes extra effort
>>>> which translates to opportunity costs ( such as Battlefield 2142
>>>> time ) so I will not
>>>> pursue more knowledge in detail if I can not verify the source
>>>> beforehand.
>>>> The distance seems 600 miles to 700 miles from here maybe
>>>> magnitude 4
>>>> but nothing seems to match that as of my last look.
>>>> Regards;
>>>> geoff
>>>> -
>>> __________________________________________________________
>>> Public Seismic Network Mailing List (PSN-L)
>>> To leave this list email PSN-L-REQUEST@.............. with the body
>>> of the message (first line only): unsubscribe
>>> See http://www.seismicnet.com/maillist.html for more information.
>> __________________________________________________________
>> Public Seismic Network Mailing List (PSN-L)
>> To leave this list email PSN-L-REQUEST@.............. with the body
>> of the message (first line only): unsubscribe
>> See http://www.seismicnet.com/maillist.html for more information.
> __________________________________________________________
> Public Seismic Network Mailing List (PSN-L)
> To leave this list email PSN-L-REQUEST@.............. with
> the body of the message (first line only): unsubscribe
> See http://www.seismicnet.com/maillist.html for more information.
--
Best regards,
Angel
__________________________________________________________
Public Seismic Network Mailing List (PSN-L)
[ Top ]
[ Back ]
[ Home Page ]