Bulletin of the Seismological Society of America
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
QUICK SEARCH:   [advanced]


     

Bulletin of the Seismological Society of America; October 1988; v. 78; no. 5; p. 1693-1706
© 1988 Seismological Society of America
This Article
Right arrow Full Text (PDF)
Right arrow References
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
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by KING, N. E.
Right arrow Articles by WYATT, F.
Right arrow Search for Related Content
GeoRef
Right arrow GeoRef Citation

Comparing strain events: A case study for the Homestead Valley earthquakes

N. E. KING, D. C. AGNEW and F. WYATT

INSTITUTE OF GEOPHYSICS AND PLANETARY PHYSICS SCRIPPS INSTITUTION OF OCEANOGRAPHY, A-025 UNIVERSITY OF CALIFORNIA, SAN DIEGO, LA JOLLA, CALIFORNIA 92093

Abstract

We present a procedure for comparing strain events at different sites, and apply it to observations for the Homestead Valley earthquake sequence of 15 March 1979. Coseismic strain steps occurred on two laser strainmeters at Piñon Flat Observatory (PFO) and on a creepmeter spanning the San Andreas fault at Wiebe Ranch (XWR); the creepmeter records were studied by Leary and Malin (1984). The PFO coseismic strains are consistent with a source model derived from near-field geodetic measurements, while the XWR coseismic extension is 1200 times too large and of the wrong sign. The XWR instrument showed an anomalous extension about 20 hours before the earthquake (Leary and Malin, 1984), but no such signals were detected on the PFO strainmeters at this time. To compare these preseismic observations we must make some assumption about the preseismic source, and we choose to assume that any precursory slip occurred on the fault plane that eventually ruptured. Under this assumption, the preseismic XWR and PFO records cannot be reconciled unless the preseismic dislocation is left-lateral or mostly thrust, and the fault zone at XWR magnifies strain by a factor of 2900 or more. This strain magnification implies that the fault-zone shear modulus at XWR is 107 Pa, three orders of magnitude smaller than the shear modulus of typical crustal rocks. However, earth-tide observations at XWR constrain the strain magnification at this site to be less than about 55. Thus the preseismic extension at XWR is probably not a precursor to the Homestead Valley earthquake.




This article has been cited by other articles:


Home page
 Bulletin of the Seismological Society of AmericaHome page
G. C. P. King, R. S. Stein, and J. Lin
Static stress changes and the triggering of earthquakes
Bulletin of the Seismological Society of America, June 1, 1994; 84(3): 935 - 953.
[Abstract] [PDF]

Home page
 ScienceHome page
R. S. Stein, R. S. Stein, G. C. P. King, and J. Lin
Change in Failure Stress on the Southern San Andreas Fault System Caused by the 1992 Magnitude = 7.4 Landers Earthquake
Science, November 20, 1992; 258(5086): 1328 - 1332.
[Abstract] [PDF]

Home page
 Bulletin of the Seismological Society of AmericaHome page
Y. BEN-ZION, T. L. HENYEY, P. C. LEARY, and S. P. LUND
Observations and implications of water well and creepmeter anomalies in the Mojave segment of the San Andreas fault zone
Bulletin of the Seismological Society of America, December 1, 1990; 80(6A): 1661 - 1676.
[Abstract] [PDF]


HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
Copyright © 1988 by the Seismological Society of America.