Doug,
It sounds like most of the people on this list would have  
the equipment needed to reproduce the gadgets listed.  
Would it be practical to throw a geophone in the 
back yard and try this as a weekend project or is some 
magic done inside the box?  What kind of sample rate would
they use?

I might not see much in my case, since I live on top of a 
thick layer of glacial muck (Southeast Michigan).

Jack Ivey

> -----Original Message-----
> From: Doug Crice [mailto:dcrice@.............
> Sent: Thursday, February 07, 2002 11:00 AM
> To: psn-l@..............
> Subject: Re: 2 items of seis interest on ebay
> 
> 
> 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.
> 
> Doug
> 
> 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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