In a message dated 2006/10/08, joe.armstrong@............. writes:

> I live in a subdivision in a city in Central Illinois. The geological 
> survey tells my that in my area, that bedrock is 10-30' feet below. I have a 
> basement, but also two active kids. I am interested in having a seismometer that 
> would be capable of detecting New Madrid activity.
>  
> So far my attempts have involved the construction of a 8" coil using #34 
> wire on a 3' - 3" pvc form using a pendulum of 6 magnetron magents. Coil: 
> Resistance of ~7.1kohm.  
> After I also have 3 - 4.5hz geophones.

Hi Joe,

       What are you calling 'Magnetron Magnets', please? What shape and size? 
Are they the donut type out of microwave cookers? Or the large horse shoe 
types, maybe up to 10" across the base from radar sets? See 3 & 4th  photos from 
bottom at http://pages.prodigy.net/fxc/JC.html

       If you mount ANY magnets on the seismometer arm, you will likely find 
it very noisy. Seismometers may be capable of measuring movements down to a 
few 10s of nano metres. 1 thou of an inch = 25,400 nano metres. 
       Magnets mounted on a seismometer arm are likely to pick up every large 
pulse on the house utility wiring, fridges turning on and off, washing 
machines, passing cars, trucks and trains, changes in the Earth's magnetic 
field...... This is definitely NOT a good idea.

       You should plan on putting the coil on the arm and on using a non 
magnetic mass. Brass is easy to machine. Lead and copper are also OK. If you use a 
horizontal copper plate(s) for the mass, you can damp it directly with 
magnets.
       I suggest that you stay clear of oil damping. It is temperature 
sensitive, relatively difficult to set up correctly and tends to be messy. 

 My questions follow:
> 1) Can you think of a project that I use the on-hand coil and magnets or 
> the geophones? Or should I just start over with another project?

           The coil is rather too large for ease of use. You may be able to 
buy 'spare coils' for sequence timers used on washing machines? 
    The size depends on the dimension of the magnet poles and the layout. You 
usually use a hollow section  / ring coil of about the same diameter. 

    You might want to consider using NdFeB magnets? They give a much higher 
output and are 'affordable'.
    I use 1" square Neos in a quad arrangement with a rectangular coil about 
1.25" long by 3/4" wide internal and 2,500 turns of finer wire. Resistance 
about 500 Ohm.
     See http://jclahr.com/science/psn/chapman/lehman/index.html

    Are the geophones the 4.5 Hz triaxial plastic cased ones that Larry 
sells?

       If so, I suggest that you get the geophones 'up and runnning' first to 
'get some experience'. Larry at http://psn.quake.net/ sells amplifiers and an 
ADC for seismic work. Maybe try the geophones out at various locations to 
find out what other local and surface signals there are? 

> 2) Basement: Is it a suitable location? I have been told that that gravel 
> under the basement disperses most of the vibration. Would the activity of the 
> kids affect the readings? Should the seimometer be physically secured to the 
> concrete?

       The basement would likely be the best place to start with. Does it 
have a concrete floor? 
       Alternatively, can you provide a shed or some protection in the 
garden, away from the house or nearby tall trees?
       You will likely find that the seismic signals will get through the 
gravel quite OK.

       You don't say anything about your kid's size, weight or activities!

       Your geophones should sit on concrete OK, but for long term use you 
should consider siting them maybe 20 ft or more from the house and underground, 
maybe 2 to 3 ft deep in a waterproof container? There is a lot of 'surface 
noise' about, which you probably don't want to see.

       If you are mounting a Lehman type seismometer on concrete, it is a 
good idea to provide three glazed tiles / glass squares / metal plates glued to 
the concrete with pool adhesive or similar to provde a hard even surface for 
the levelling screws. I use 2" squares of 1/8" stainless steel. 
       You may be able to reduce local / house noise a lot by low pass 
filtering down to 5 or 3 Hz.

       How far down is the water table? I was wondering if you could cut a 
hole in the basement floor and cast a separate concrete pillar directly into the 
gravel underneath? This could 'isolate you' to some extent from the 
activities in the house. Try using the existing floor first though, away from outside 
walls or any support pillars.  

> 3) Can a home brew seismometer be effective in Central Illinois?

       I can see absolutely no reason why not!! 
       But do expect to see local environmental and house associated noise. 
You need to train yourself to recognise what earthquake signals look like and 
to identify other noise types and patterns.
       You will likely see quite a few local quakes which do not get reported 
on a WW information database, but which may or may not get reported on USGS. 
You may also see blasts from quarrying. 

       Regards,

       Chris Chapman
In a me=
ssage dated 2006/10/08, joe.armstrong@............. writes:



I live in a subdivision in a ci=
ty in Central Illinois. The geological survey tells my that in my area, that=
 bedrock is 10-30' feet below. I have a basement, but also two active kids.=20=
I am interested in having a seismometer that would be capable of detecting N=
ew Madrid activity.

 

So far my attempts have involved the construction of a 8" coil using #34 wir=
e on a 3' - 3" pvc form using a pendulum of 6 magnetron magents. Coil: Resis=
tance of ~7.1kohm.  

After I also have 3 - 4.5hz geophones.




Hi Joe,



       What are you calling 'Magnetron Magnets=
', please? What shape and size? Are they the donut type out of microwave coo=
kers? Or the large horse shoe types, maybe up to 10" across the base from ra=
dar sets? See 3 & 4th  photos from bottom at http://pages.prodigy.n=
et/fxc/JC.html



       If you mount ANY magnets on the seismom=
eter arm, you will likely find it very noisy. Seismometers may be cap=
able of measuring movements down to a few 10s of nano metres. 1 thou of an i=
nch =3D 25,400 nano metres. 

       Magnets mounted on a seismometer arm ar=
e likely to pick up every large pulse on the house utility wiring, fridges t=
urning on and off, washing machines, passing cars, trucks and trains, change=
s in the Earth's magnetic field...... This is definitely NOT a good idea.


       You should plan on putting the coil on=20=
the arm and on using a non magnetic mass. Brass is easy to machine. Lead and=
 copper are also OK. If you use a horizontal copper plate(s) for the mass, y=
ou can damp it directly with magnets.

       I suggest that you stay clear of oil da=
mping. It is temperature sensitive, relatively difficult to set up correctly=
 and tends to be messy. 



 My questions follow:

1) Can you think of a project=20=
that I use the on-hand coil and magnets or the geophones? Or should I just s=
tart over with another project?




           The coil is rat=
her too large for ease of use. You may be able to buy 'spare coils' for sequ=
ence timers used on washing machines? 

    The size depends on the dimension of the magnet poles and=
 the layout. You usually use a hollow section  / ring coil of about the=
 same diameter. 



    You might want to consider using NdFeB magnets? They give=
 a much higher output and are 'affordable'.

    I use 1" square Neos in a quad arrangement with a rectang=
ular coil about 1.25" long by 3/4" wide internal and 2,500 turns of finer wi=
re. Resistance about 500 Ohm.

     See http://jclahr.com/science/psn/chapman/lehman/in=
dex.html



    Are the geophones the 4.5 Hz triaxial plastic cased ones=20=
that Larry sells?



       If so, I suggest that you get the geoph=
ones 'up and runnning' first to 'get some experience'. Larry at http://psn.q=
uake.net/ sells amplifiers and an ADC for seismic work. Maybe try the geopho=
nes out at various locations to find out what other local and surface signal=
s there are? 



2) Basement: Is it a suitable l=
ocation? I have been told that that gravel under the basement disperses most=
 of the vibration. Would the activity of the kids affect the readings? Shoul=
d the seimometer be physically secured to the concrete?




       The basement would likely be the best p=
lace to start with. Does it have a concrete floor? 

       Alternatively, can you provide a shed o=
r some protection in the garden, away from the house or nearby tall trees?
       You will likely find that the seismic s=
ignals will get through the gravel quite OK.



       You don't say anything about your kid's=
 size, weight or activities!



       Your geophones should sit on concrete O=
K, but for long term use you should consider siting them maybe 20 ft or more=
 from the house and underground, maybe 2 to 3 ft deep in a waterproof contai=
ner? There is a lot of 'surface noise' about, which you probably don't want=20=
to see.



       If you are mounting a Lehman type seism=
ometer on concrete, it is a good idea to provide three glazed tiles / glass=20=
squares / metal plates glued to the concrete with pool adhesive or similar t=
o provde a hard even surface for the levelling screws. I use 2" squares of 1=
/8" stainless steel. 

       You may be able to reduce local / house=
 noise a lot by low pass filtering down to 5 or 3 Hz.



       How far down is the water table? I was=20=
wondering if you could cut a hole in the basement floor and cast a separate=20=
concrete pillar directly into the gravel underneath? This could 'isolate you=
' to some extent from the activities in the house. Try using the existing fl=
oor first though, away from outside walls or any support pillars.  



3) Can a home brew seismometer=20=
be effective in Central Illinois?




       I can see absolutely no reason why not!=
! 

       But do expect to see local environmenta=
l and house associated noise. You need to train yourself to recognise what e=
arthquake signals look like and to identify other noise types and patterns.<=
BR>
       You will likely see quite a few local q=
uakes which do not get reported on a WW information database, but which may=20=
or may not get reported on USGS. You may also see blasts from quarrying. 


       Regards,



       Chris Chapman