Dan -

One though to keep in mind when you talk about "representative =
stations."  The signal received at each seismometer is a summation of =
all the modifications to the seismic wave by the terrain that it passed =
through.

Body (P & S) waves and their variations travel through the earths core =
(below the mantel) and are reflected and/or refracted by the different =
material that they passes through.

Surface (Love and Rayleigh) waves on the other hand follow the crust of =
earth, bouncing between the mantel and the free surface.  These waves =
are extensively modified as they pass through both thick (continental), =
and thin (oceanic) crusts.

Another factor to consider is the focal mechanism of the event.  There =
are azimuths where you have a null or near null signal, while other =
azimuths have peak intensity.  For example the peak amplitude for the P =
wave does not correspond to the peak amplitude for the S wave.  They are =
45 degrees out of phase.  The peak amplitudes of the Love & Rayleigh =
waves are similarly out of phase.  In other words are your seismometers =
on an azimuth for peak signals or null signals.

Depth is another consideration.  As depth increases the amplitude of the =
surface waves decrease while the observed amplitude of the body waves =
increase.  At depths greater than 100 km surface waves fade out =
noticeably, while we earthquakes occur at depths greater than 600 km.

Distance is another consideration.  Body waves and surface waves follow =
different paths and are not modified the same.  This is particularly =
evident as range increases.

A lot of seismic research is done by grids, the installation of multiple =
seismometers in some type of grid pattern over an area of interest.  =
They wait for an event and then observe how the waves are modified =
within the grid.  In other words did the wave pass through the grid =
faster or slower than expected, was it modified or otherwise changed =
while in the grid.

There are many seismic arrays throughout the world.  Some of dense and =
others are widely scattered. =20

I think it would be difficult at best to find a group of representative =
stations.   It all depends upon what you want to observe.=20

Bob Hancock


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