I asked Larry about this and he wanted me to post it here. I think he 
was trying to get rid of me. It probably shows how little I know and 
that I am missing something. This question came out of the activity in 
the Guy area which is about 500 miles west of me as well as the New 
Madrid system which is closer. It seems the records are better on the 
2-4 Hz units. Here was my question;

> It is about this geophone vs lehman or other long period instruments. In
> California you have many local quakes. These quakes have frequencies
> higher than long distance quakes. What is the logic of (just/or 
> popularity of) long
> period instruments out there? What precipitated this trend? The 1-5 Hz 
> units should be better on local events -- which you have a lot.
There are many California quakes and there is the activity in Washington 
State and Yellowstone but you never see local seismic detectors being 
posted with periods of 1-4.5 Hz -- except possibly tchannel.  Shouldn't 
these units help differentiate human noises like quarry activity from 
smaller local earthquake activity?

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