PSN-L Email List Message

Subject: Re: are these real?
From: "Connie and Jim Lehman" lehmancj@...........
Date: Sun, 9 May 2004 16:47:35 -0400

Dick--I had a look at the records, and am unable to decipher exactly what
you are seeing.  You may wish to concentrate on only one sensor and get to
within the parameters expected.  It looks as you have unusual noise, or
microseisms that you amplify at the expense of a valid p, s, & l wave
arrival.  Microseisms are our friends, as they tell us the system is working
normally, but an incoming event should ride well above microseismic level.
You speak of filtering, and I know this is an area of expertise much of
which I am not familiar with.  In long period sensors, the only filtering I
was concerned with was 60 hz power noise, and an occasional mechanical noise
depending on the location of the sensor to a mechanical room in the area.
Usually a simple passive filter took out the chatter........  I rather doubt
the rock quaries or strip mines have any influence on your site at the
distances given.
  If you work with the "Lehman" design, bring that period up to at least 15
seconds---adjust the damping to within the limits and set the gain to see
microseisms at a low level all the time--and events should show----------
     Best wishes,  Jim Lehman
----- Original Message -----
From: "tdick" 
Sent: Friday, May 07, 2004 11:41 PM
Subject: Re: are these real?

> > angel
> >
> I suppose I am trying to filter too much. Look at just the Guatemala quake
> of the 3d of May -- a big one. It was triggered by WinSDR. (The
> that I first saw 50 years ago didn't have all this filtering.) I think you
> expect to see seismograms that look like test 1 and test 1a -- not in a
> folder -- right?? -- same data used to do those in the May folder.  I
> get away from seeing the wave shape at "P" and "S" etc. so the horizontal
> units appeal to be -- as well as too much filtering; the east-west
> seems to lack sensitivity - even the north-south picks up this quake
> I am in a high noise area. The geophones are buried four foot down about
> feet from a 4 1/2 acre lake. The Lehmans and HM vertical are about the
> depth but in the basement of the house. There are two strip mines (coal)
> within forty miles and two rock quarries within 120 miles. The house is
> fifty years old and was built on swamp land. Period on the Lehmans is
> 5 secs -- I have no idea what the vertical is.
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