Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

This Article Full Text (PDF) References Alert me when this article is cited Alert me if a correction is posted 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 HighWire Citing Articles via Google Scholar Google Scholar Articles by BOORE, D. M. Articles by STIERMAN, D. J. Search for Related Content GeoRef GeoRef Citation

Source parameters of the Pt. Mugu, California, earthquake of February 21, 1973

DEPARTMENT OF GEOPHYSICS STANFORD UNIVERSITY, STANFORD, CA 94305

Abstract

Strong-motion recordings at Port Hueneme and Pasadena, at hypocentral distances of 24 and 80 km, respectively, have been fit with a number of commonly used dislocation models. The most satisfactory model is a fault in which rupture spreads circularly from the focal point (Savage, 1966). The derived model shows bilateral rupture with a lower bound on the moment of 1.5 x 10²⁴ dyne-cm. With an assumed rupture velocity of 3.1 km/sec the stress drops are in the range of 50 to 200 bars. The moment of the initial rupture is well determined, but much uncertainty can exist in the other fault parameters. For example, if the rupture velocity is 1.55 km/sec, an equally good fit to the Port Hueneme record can be achieved, but a stress drop close to 4000 bars is required. The area of the initial rupture is smaller than the area outlined by the aftershock distribution. There is evidence in the Port Hueneme record that the rupture process involved a multiple earthquake, which would help explain the inconsistency between the initial slip area and the area shown by aftershocks. Studies of one-dimensional wave propagation through the sediments beneath the Port Hueneme station suggest that the surface motions have been amplified by a factor of about 2.8 compared with an equivalent bedrock recording, although the wave forms have not been distorted significantly. The observed motions were compensated for the effect of the sediments before the model fitting.

A comparison of different dislocation models shows that rupture propagation effects are important in fitting the observed motions and that if the finite extent of the rupture surface is accounted for, the ^–2 high-frequency decay of the displacement spectrum often attributed to the Haskell dislocation model should be closer to ^–3.

This article has been cited by other articles:

				A. L. BENT and D. V. HELMBERGER Seismic characteristics of earthquakes along the offshore extension of the western transverse ranges, California Bulletin of the Seismological Society of America, April 1, 1991; 81(2): 399 - 422. [Abstract] [PDF]

				W. B. JOYNER A scaling law for the spectra of large earthquakes Bulletin of the Seismological Society of America, August 1, 1984; 74(4): 1167 - 1188. [Abstract] [PDF]

				W. B. JOYNER and D. M. BOORE Peak horizontal acceleration and velocity from strong-motion records including records from the 1979 imperial valley, California, earthquake Bulletin of the Seismological Society of America, December 1, 1981; 71(6): 2011 - 2038. [Abstract] [PDF]

				J. BOATWRIGHT Quasi-dynamic models of simple earthquakes: Application to an aftershock of the 1975 Oroville, California, earthquake Bulletin of the Seismological Society of America, February 1, 1981; 71(1): 69 - 94. [Abstract] [PDF]

				J. BOATWRIGHT A spectral theory for circular seismic sources; simple estimates of source dimension, dynamic stress drop, and radiated seismic energy Bulletin of the Seismological Society of America, February 1, 1980; 70(1): 1 - 27. [Abstract] [PDF]

				D. M. BOORE and W. B. JOYNER The influence of rupture incoherence on seismic directivity Bulletin of the Seismological Society of America, April 1, 1978; 68(2): 283 - 300. [Abstract] [PDF]

				R. O. CASTLE, J. P. CHURCH, M. R. ELLIOTT, and J. C. SAVAGE Preseismic and coseismic elevation changes in the epicentral region of the Point Mugu earthquake of February 21, 1973 Bulletin of the Seismological Society of America, February 1, 1977; 67(1): 219 - 231. [Abstract] [PDF]

				D. J. STIERMAN and W. L. ELLSWORTH Aftershocks of the February 21, 1973 Point Mugu, California earthquake Bulletin of the Seismological Society of America, December 1, 1976; 66(6): 1931 - 1952. [Abstract] [PDF]