PSN-L Email List Message
Subject: Seismic clipping levels
From: Brett Nordgren Brett3kg@.............
Date: Mon, 15 May 2006 10:15:51 -0400
To all,
There is a relatively new USGS report that gives the maximum expected
ground motion at 87 continental US locations (the UNSS backbone stations)
for the purpose of testing instrument clipping levels. Clipping levels and
max ground motion is a subject that fairly regularly comes up on PSN-L and
this data may help provide some good guidance. The report can be
downloaded from http://pubs.usgs.gov/of/2005/1437/
To come up with the data the authors had to do some extremely complex
statistical work which I am currently trying to understand, but it's clear
that coming up with good data isn't easy. Their numbers give the ground
motion levels that had a 10% chance of being exceeded in a time period of
30 years. That's probably way too conservative for amateur work; better
would probably be 10% in 1 year or even 50% in 1 year. I'm trying to
understand their process well enough to be able to manipulate the raw data
to get those, but I still have a lot to learn.
I've put the results in an Excel
file http://bnordgren.org/seismo/station_pgv.xls (164kb) in a form that
includes spectrum charts, which should be useful to compare with individual
instrument clipping levels. And the general process should be useful in
evaluating sites anywhere in the world.
If anyone who really understands this stuff can point me to resources
relating to the statistical methods and raw data sources, I would be most
grateful.
Regards,
Brett
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