HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) References Citation Map Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by SILVER, P. Search for Related Content

Retrieval of source-extent parameters and the interpretation of corner frequency

DEPARTMENT OF TERRESTRIAL MAGNETISM CARNEGIE INSTITUTION OF WASHINGTON, 5241 BROAD BRANCH ROAD, N.W., WASHINGTON, D.C. 20015

Abstract

A method is proposed for retrieving source-extent parameters from far-field body-wave data. At low frequency, the normalized P- or S-wave displacement amplitude spectrum can be approximated by |^(r^,)| = 1 – ²(r^)²/2 where r^ specifies a point on the focal sphere. For planar dislocation sources, ²(r^) is linearly related to statistical measures of source dimension, source duration, and directivity. ²(r^) can be measured as the curvature of |^(r^,)| at = 0 or the variance of the pulse ^(r^,t). The quantity is contrasted with the traditional corner frequency ₀, defined as the frequency at the intersection of the low- and high-frequency trends of |^(r^,)|. For dislocation models without directivity, _c(P) _c(S) for any r^. A mean corner frequency defined by averaging ²(r^) over the focal sphere, , satisfies _c(P) > _c(S) for any dislocation source. This behavior is not shared by ₀. It is shown that ₀ is most sensitive to critical times in the rupture history of the source, whereas _c is determined by the basic parameters of source extent. Evidence is presented that _c is the corner frequency measured on actual seismograms. Thus, the commonly observed corner frequency shift (P-wave corner greater than the S-wave corner), now viewed as a shift in _c is simply a result of spatial finiteness and is expected to be a property of any dislocation source. As a result, the shift cannot be used as a criterion for rejecting particular dislocation models.