This is a very late comment on the local noise question.

In exploration seismic work geophone arrays were used to filter local noise.
The signals from several geophnes would be summed.  The noise would be out
of phase at the geophones but the signal would be in phase.  In reflection
work that assumption is more justified than in earthquake or refraction
seismology as in reflection the signal is coming more or less straight up.

Has this ever been used in earthquake seismology?  The usual answer to noise
is a quiet location but with educational seismometers rather than research
seismometers, location near the classroom is important.

Second.  There is a new chip that is up to a 6 pole analog filter.   The
configuration of the filter is set in a device similar  to an EPROM burner.
The software that comes with it has full design features such as  simulation
of amplitude and phase.  Unfortunately I threw the flier away but I am
trying to find the manufacturer through other channels.   This could be
helpful in designing filters for local noise.  If anyone knows the web site
of the manufacturer please let me know.  I will continue to try to find it
by other sources,

Tom Schmitt

tschmitt@..............

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