For hammer work, you use sample rates on the order of 100 microseconds
(10,000 sample/sec). The veolcities might run something like this:

Soil	1000-2000 ft/sec (300-600 m/s)
clays, weathered rock	2000-5000 ft/sec (600-1500 m/s)
groundwater	5000 ft/sec (1500 m/s)
bedrock	5000-15000 ft/sec (1500-7500 m/s)

So, even though the block diagram is similar, you scale the frequencies
about three orders of magnitude. Modern exploration seismographs can be
seen at my old company http://www.geometrics.com/  Anybody who wants to
look at the solutions in more detail should go to
http://www.geometrics.com/sci.html and download the booklet "Seismic 
Refraction Exploration for Engineering Site Investigations"

Doug

Jack Ivey wrote:
> 
> 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?
>
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