PSN-L Email List Message

Subject: Recording Micro Quakes
From: Roger Sparks rsparks@..........
Date: Mon, 20 Feb 2006 13:54:46 -0800

This is a re-post.   I mistakenly originally posted in HTML format, 
which does not reproduce well on PSN.  I locked my E-mail to "text" for 
this posting and all future postings. 

Hi Bryan,

You should find that your Lehmann would be more sensitive than a 
Geophone at the higher frequencies expected from micro quakes.   This 
would be because the longer period instruments would use less damping 
than the higher frequency units.

Think of it this way.   The shorter the period of a seismometer, the 
larger the damper will be to achieve critical damping.   The damper 
always reduces the motion induced in the seismometer by the passing 
wave.   Larger damper for a higher frequency sensor so less sensitivity 
(than the longer period sensor) at the higher frequencies.

You might consider if the damping and filters you are using on the 
Lehmann are seriously attenuating the higher frequency waves that could 
be expected from micro quakes.   You are probably sensing the micro 
quakes now, but losing the information in the filters and damper.

Several people are posting recordings of micro quakes on  A WinQuake FFT analysis of the posted micro 
quakes helps give a perspective of the bandpass requirements needed of 
the equipment.

Best wishes,   Roger

psn-l-digest-request@.............. wrote:

>.------ ------ ------ ------ ------ ------ ------ ------ ------ ------.
>| Message 1                                                           |
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>From:    1goss@...........
>Date:    Fri, 17 Feb 2006 08:54:25 +0000
>Hi all I am trying to find a used geophone for recording micro earthquakes in the central US.
>Mainly in the New Madrid Fault Zone. I have a Lehmann sensor, but I would like a Geophone. 
>I am not sure what I need, Maybe something like Larry had on his website but is sold out of the GeoSpace HS 10-1 1 Hz Vertical Sensor. Where would I look to find one or does anyone have one they would part with for the right price.
>Thanks Bryan S Goss
>Corinth Ms

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