Quick
Search: 		  
advanced search
 GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help 
Bulletin of the Seismological Society of America Signup for GSW Email News
JOURNAL HOME HELP CONTACT PUBLISHER SUBSCRIBE ARCHIVE SEARCH TABLE OF CONTENTS
Bulletin of the Seismological Society of America; October 1996; v. 86; no. 5; p. 1447-1458
© 1996 Seismological Society of America
This Article
Right arrow Full Text (PDF)
Right arrow References
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by van de Vrugt, H.
Right arrow Articles by Weddberg, J.
Right arrow Search for Related Content
GeoRef
Right arrow GeoRef Citation

Inversion of local earthquake data for site response in San Diego, California

H. van de Vrugt, S. Day, H. Magistrale and J. Weddberg*

Department of Geological Sciences San Diego State University, San Diego, California 92182-1020

Abstract

Portable seismic stations were deployed in the San Diego area to investigate local site effects on weak ground motion. We analyzed horizontal S-wave recordings from 161 local and near-regional earthquakes, using a least-squares matrix factorization (LSMF) inversion algorithm to separate the site effects from the combined effects of the source and path. Recording sites included stations underlain by Holocene fill, alluvium, bay sediments and artificial fill, Quaternary and Tertiary formational deposits, and crystalline rock exhibiting various degrees of weathering. Spectral ratios of S-wave coda were also used to estimate site response at two of the study sites. The coda analysis results were consistent with the results obtained from the inversion analysis. Results indicate that severe amplifications are present at some sites underlain by holocene deposits but demonstrate that surface geology alone provide an inadequate foundation for microzonation. Site-response amplifications up to a factor of 15, relative to a crystalline rock reference site, were observed at one site underlain by artificial fill and bay sediments. Yet a second site underlain by bay sediments exhibited a site response nearly 75% lower than the other bay sediment site, consistent with the site response observed at sites underlain by more indurated deposits. The site response observed at the Quaternary and Tertiary sedimentary sites was fairly consistent with the response of the younger alluvial sites, which may be attributable to the relatively shallow burial of the formational deposits in San Diego. The site responses at all five crystalline rock sites included in the study were very similar at frequencies below 4 Hz, and four of the five were similar up to 10 Hz, becoming more distinct at higher frequency. Seismic P-wave and S-wave refraction data collected at the crystalline rock sites demonstrate that deviations in response at higher frequencies are attributable to the presence of weathered horizons in the near surface at these sites.

Footnotes

* Present address: Department of Earth Sciences, University of Southern California, Los Angeles, California 90089-7040.






JOURNAL HOME HELP CONTACT PUBLISHER SUBSCRIBE ARCHIVE SEARCH TABLE OF CONTENTS
Copyright © 2009 by Seismological Society of America