PSN-L Email List Message

Subject: Re: N.Calif event
From: Edward Cranswick cranswick@........
Date: Thu, 16 Mar 2000 22:57:54 -0700

    I was intrigued by your question so I used it as an excuse to get my
WinQuake act together and install the most recent version, v 2.6.
    A M5.8 earthquake is going to have an S-wave corner frequency near 1
Hz, and it can also generate alot of Raleigh waves on the vertical that are
peaked at even lower frequencies. The S-wave corner frequency is controlled
by the fault dimension, and to first order, it is equal to the reciprocal
of the S-wave travel time along the fault, i.e., the fault length divided
by the S-wave velocity. I looked at the spectra of your record and noted
that it was flat from about 10 Hz (where you must have your low-pass,
anti-aliasing-filter corner frequency) down to 0.5 Hz where your high-pass
is. It would be interesting to see the record before you high-passed it: it
should start rolling off at lower frequencies somewhere just below 1 Hz. In
the absence of instrument response, in theory, the acceleration spectrum
should be flat in the band that extends from the S-wave corner-frequency up
to f_max -- the high-frequency limit caused by the low-pass filter
characteristics of the Earth.

barry lotz wrote:

>  Hi
>     I've uploaded a new event file for a small vertical "strong motion"
> accelerometer. I'm not to familiar with acceleration recording accept
> that I realize the frequency content is a higher. I increased my sample
> rate for the Lehman and this sensor to 50 hz. I was surprised to get
> little long period content in this  recording. Is this common for
> accelerations?

Edward Cranswick                Tel: 303-273-8609
US Geological Survey, MS 966    Fax: 303-273-8600
PO Box 25046, Federal Center    cranswick@........
Denver, CO 80225-0046  USA      E.M. Forster said, "Only connect".


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Larry Cochrane <cochrane@..............>