PSN-L Email List Message

Subject: Re: 2 items of seis interest on ebay
From: Doug Crice dcrice@............
Date: Thu, 07 Feb 2002 07:59:30 -0800

These are "exploration" seismographs, commonly used by engineering
geologists and such to look at geologic structure for the first several
meters below the surface. You use a sledgehammer as the energy source
and a single geophone as the receiver.

You start the survey with the hammer and geophone about 3 meters apart,
hit the ground, and display the seismic record on a small CRT. An impact
switch on the hammer determines the zero time and the arrival time at
the geophone is measured with a cursor on the CRT.

Next, you move the hammer to say 6 meters and do it again, continuing
the move-hammer-move process untill you are far enough to see what you
are looking for or until the hammer isn't strong enough to overcome the
background vibrations.

Each of the arrival times are plotted on a graph, which the operator
uses to calculate the seismic velocities and the thickness of the
geologic layers (which usually are things like soil, weathered rock,
groundwater level, and bedrock).

These type of instruments are still in use. These particular ones are
over 30 years old. If they are broken, repair parts may not be available
and of course they are absolutly no use for earthquake measurements. The
seller's price expectations seem ambitious to me, but you only need two
suckers to get a good price.


BOB BARNS wrote:
> Hi,
> On ebay:
> Bison Signal Enhancement Seismograph
> 1570B                                         Item # 1701927467
> ends 2/13
> SoilTest MD-5 Engineering Seismograph
> Geophon                                         Item # 1701923739
> ends 2/13
> Bob

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