In a message dated 29/03/2010, amej@............. writes:

I am  reading the specs for the VolksMeter instrument. There is a 2-channe=
l=20
or  single channel instrument.
Is this a good one to get? Which one?
Is  there a better instrument to purchase near this price, including=20
software  and USB output?
Dear Dick Harbegger,
=20
    This depends on what you want to do. You see a  range of seismic=20
signals depending on the distance from the quake to your  sensor. The high=
er=20
frequency signals are absorbed as they travel through the  earth. Local qu=
akes=20
can generate fast P waves up to 10 Hz. Near Regional quakes  up to 5 Hz,=
 far=20
Regional quakes up to about 3 Hz and teleseismic quakes up to  about 2 Hz.=
=20
The S waves which follow them are usually at about 1/2 of the P wave =20
frequency. When these waves strike the surface of the earth, they generate=
 much =20
slower surface transverse Love waves and vertical Rayleigh waves with peri=
ods =20
typically of 15 to 25 seconds, but you sometines see additional waves at=
=20
about  40 seconds, or at even longer periods from the occasional great qua=
kes.=20
You also  see environmental noise and microseism ocean background noise,=
=20
usually at about  5 to 6 seconds period
=20
    Have a look at the 1960's Seismograph Training  Manual at=20
_http://psn.quake.net/info/analysis.pdf_ (http://psn.quake.net/info/analys=
is.pdf)=20
=20
    The Volksmeter is a horizontal sensor. It is sold  in either a single=
=20
channel version or with two channels at right angles. It is  basically a=
 0.9=20
second pendulum with a digitally extended response under  your control out=
=20
to about 1000 seconds.=20
    See plots on  http://psn.quake.net/currentseismicity.html

My funds  are limited, but I would enjoy the features of this type of=20
instrument.
I  have been told that this is a horizontal movement device and I would=20
need one  that includes a vertical sensor. True?
I am at a stage where I do not want  to re-invent the wheel, or piece=20
something together.
    NOT TRUE! Most professional sensors are triaxial  and they rely on=20
vertical signals to determine the quake magnitude. This was  first done by=
=20
Richter using horizontal Wood-Anderson type sensors and it can  still be=
 done=20
this way.

I am  located in the high desert of Southern California, near the San=20
Andreas  fault.
I was a participant to the former Seismic Pre-Cursor Net (W6FXN) on  the=
=20
2-Meter HAM Band.
This was when "dog and cat" reports were experimental  and others measured=
=20
water well heights.

I always enjoy reading the  messages, especially from J=F3n in the cold=20
North. The expertise is too much for  me to comment.


Two single channel horizontal types and one single  channel vertical /=20
triaxial type are listed on=20
_http://www.bgs.ac.uk/education/school_seismology/seismometer.html_=20
(http://www.bgs.ac.uk/education/school_seismology/seismometer.html)    The=
  single channel horizontal types have a response from 5 Hz to=20
over 20  seconds, covering almost all of the shake range in practice. The=
=20
CMG-EDU Guralps  were used in the PEPP initiatives back in the mid 1990's=
 and=20
have a response of  30Hz to 30 seconds. They are semi professional sealed=
=20
designs and are  calibrated.
=20
    Horizontal sensors are hardly effected by  atmospheric pressure noise,=
=20
but they do see ground tilt noise, which increases  at periods over ~20=20
seconds and limits the very long period detection  capability.
    A bare vertical sensor may see VERY SERIOUS wide  band atmospheric=20
pressure noise, which is why they need to be either  compensated for this,=
 or=20
sealed in an airtight chamber. The chamber  suspension needs to designed=
 so=20
that air pressure changes are not  communicated to the sensor. They are ne=
arly=20
immune to ground tilt noise.
    Go to _www.iris.edu/seismon_ (http://www.iris.edu/seismon) , highlight=
=20
a local  station and select the noise plots.=20
    You need a ground level or basement low noise  location. Check the=20
references to site selection on PSN. This  is critically important !!
=20
    I hope that this helps.=20
=20
    Chris Chapman




<=
FONT id=3Drole_document   color=3D#000000 size=3D2 face=3DArial>
In a message dated 29/03/2010, amej@............. writes:
I am=20
  reading the specs for the VolksMeter instrument. There is a 2-channel or=
=20
  single channel instrument.
Is this a good one to get? Which one?
I=
s=20
  there a better instrument to purchase near this price, including 
sof=
tware=20
  and USB output?
Dear Dick Harbegger,
 
    This depends on what you want to do. You see=
 a=20
range of seismic signals depending on the distance from the quake to your=
=20
sensor. The higher frequency signals are absorbed as they travel through=
 the=20
earth. Local quakes can generate fast P waves up to 10 Hz. Near Regional=
 quakes=20
up to 5 Hz, far Regional quakes up to about 3 Hz and teleseismic quakes up=
 to=20
about 2 Hz. The S waves which follow them are usually at about 1/2 of the=
 P wave=20
frequency. When these waves strike the surface of the earth, they generate=
 much=20
slower surface transverse Love waves and vertical Rayleigh waves with peri=
ods=20
typically of 15 to 25 seconds, but you sometines see additional waves at=
 about=20
40 seconds, or at even longer periods from the occasional great quakes. Yo=
u also=20
see environmental noise and microseism ocean background noise, usually at=
 about=20
5 to 6 seconds period
 
    Have a look at the 1960's Seismograph Trainin=
g=20
Manual at http://psn.=
quake.net/info/analysis.pdf
 
    The Volksmeter is a horizontal sensor. It is=
 sold=20
in either a single channel version or with two channels at right angles.=
 It is=20
basically a 0.9 second pendulum with a digitally extended response un=
der=20
your control out to about 1000 seconds. 
    See plots on=20
http://psn.quake.net/currentseismicity.html
My funds=20
  are limited, but I would enjoy the features of this type of instrument.<=
BR>I=20
  have been told that this is a horizontal movement device and I would nee=
d one=20
  that includes a vertical sensor. True?
I am at a stage where I do not=
 want=20
  to re-invent the wheel, or piece something together.
    NOT TRUE! Most professional sensors are triax=
ial=20
and they rely on vertical signals to determine the quake magnitude. This=
 was=20
first done by Richter using horizontal Wood-Anderson type sensors and it=
 can=20
still be done this way.
I am=20
  located in the high desert of Southern California, near the San Andreas=
=20
  fault.
I was a participant to the former Seismic Pre-Cursor Net (W6FX=
N) on=20
  the 2-Meter HAM Band.
This was when "dog and cat" reports were experi=
mental=20
  and others measured water well heights.

I always enjoy reading th=
e=20
  messages, especially from J=F3n in the cold North. The expertise is too=
 much for=20
  me to comment.


    Two single channel horizontal types and one=
 single=20
channel vertical / triaxial type are listed on http://www.bgs.a=
c.uk/education/school_seismology/seismometer.html   The=
=20
single channel horizontal types have a response from 5 Hz to over 20=
=20
seconds, covering almost all of the shake range in practice. The CMG-EDU=
 Guralps=20
were used in the PEPP initiatives back in the mid 1990's and have a respon=
se of=20
30Hz to 30 seconds. They are semi professional sealed designs and are=20
calibrated.
 
    Horizontal sensors are hardly effected by=20
atmospheric pressure noise, but they do see ground tilt noise, which incre=
ases=20
at periods over ~20 seconds and limits the very long period detection=20
capability.
    A bare vertical sensor may see VERY SERIOUS=
 wide=20
band atmospheric pressure noise, which is why they need to be either=
=20
compensated for this, or sealed in an airtight chamber. The chamber=
=20
suspension needs to designed so that air pressure changes are no=
t=20
communicated to the sensor. They are nearly immune to ground tilt noise.
    Go to www.iris.edu/seismon, highlight a local=20
station and select the noise plots. 
    You need a ground level or basement low noise=
=20
location. Check the references to site selection on PSN. This=20
is critically important !!
 
    I hope that this helps. 
 
    Chris Chapman