PSN-L Email List Message

Subject: Re: seismometer/site sensitivity
From: "Geoff" gmvoeth@...........
Date: Fri, 12 Oct 2007 02:15:00 -0700

I have a vertical setup with a sensor that seems
to have a sensitivity of 1.5 to 2 volts per inches per second
and I can see a magnitude 4 about 6 degrees away.
or so it seems. I am using heavy damping to
allow me to use a single bandpass filter to equalize
the freq response of a one hertz geophone
somewhere between 4 seconds and 2 Hz.
The geophone is buried underground on a
granite tile with the base of the geophone
maybe 24 inches below ground.
Sealed to the best of my abilities
against temp and moisture and electro/magnetic fields.
My area here is extremely noisy
from vehicular traffic as well as
electrical disturbances. My station is not a very
good one but will at least let me know
when a major event happens.
The USGS was not interested in signals
from this station unless my times were the
very first and that is so very rare.
Commonly the local signals are mine blasts
which they seem to have no interest in also.
The USGS seems to have there own setup
that does not seem to miss anything at all.
You need a friend there to look for signals
you might see at your amature station
that are not earth quakes.
They are busy people there i believe
with no lower level help doing any analysis.
You most probably shall have troubles identifying
small stuff since you need several signatures to compare.
You got to compare your signals with the USGS
to get an idea what your MDL ( minimum dicernable level)
really is.
It will take time.

----- Original Message ----- 
From: "Jan Froom" 
Sent: Thursday, October 11, 2007 12:35 PM
Subject: seismometer/site sensitivity

> I'm curious how many of you have come up with a "rule of thumb" for the 
> general sensitivity of your seismometers.
> For instance I have sensed a 3.0 sixty miles out from my seismometer, 
> and have seen 5s within 300 miles.
> And I understand we should be able to sense a 7 anywhere in the world.
> But just now, I did not see a 1.3  seven miles out.
> So my question.... is this good, bad, average?
> I'm sure there are lots of variables such as type of instrument, 
> orientation, ambient noise, etc..
> but still, shouldn't there be a general feeling or rule of thumb.
> Jan in Gilroy

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