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

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   (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 



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