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Science 1 September 1978:
Vol. 201. no. 4358, pp. 814 - 817
DOI: 10.1126/science.201.4358.814

Articles

Earthquake Swarm Along the San Andreas Fault near Palmdale, Southern California, 1976 to 1977

K. C. MCNALLY 1, H. KANAMORI 1, J. C. PECHMANN 1, and G. FUIS 2

1 Seismological Laboratory, Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena 91125
2 U.S. Geological Survey, Seismological Laboratory, Division of Geological and Planetary Sciences, California Institute of Technology

Between November 1976 and November 1977 a swarm of small earthquakes (local magnitude le 3) occurred on or near the San Andreas fault near Palmdale, California. This swarm was the first observed along this section of the San Andreas since cataloging of instrumental data began in 1932. The activity followed partial subsidence of the 35-centimeter vertical crustal uplift known as the Palmdale bulge along this "locked" section of the San Andreas, which last broke in the great (surface-wave magnitude = 8frac14+) 1857 Fort Tejon earthquake. The swarm events exhibit characteristics previously observed for some foreshock sequences, such as tight clustering of hypocenters and time-dependent rotations of stress axes inferred from focal mechanisms. However, because of our present lack of understanding of the processes that precede earthquake faulting, the implications of the swarm for future large earthquakes on the San Andreas fault are unknown.

Submitted on May 8, 1978
Revised on July 10, 1978


THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
Location of earthquake swarm events near Palmdale, California, using a linear gradient velocity model.
D. S. DROWLEY and K. C. MCNALLY (1980)
Bulletin of the Seismological Society of America 70, 2145-2158
   Abstract »    PDF »



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Science. ISSN 0036-8075 (print), 1095-9203 (online)