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 HighWire Citing Articles via Google Scholar Google Scholar Articles by FITCH, T. J. Search for Related Content GeoRef GeoRef Citation

Microearthquake activity following the Parkfield, California earthquake of June, 1966

LAMONT GEOLOGICAL OBSERVATORY OF COLUMBIA UNIVERSITY, PALISADES, NEW YORK

Abstract

A high sensitivity microearthquake recording station was established 10 km from the epicenter of the magnitude 5.5 Parkfield earthquake of June 28, 1966. Beginning 43 hours after the main shock, an hourly average of 22 microaftershocks was recorded for a period of 13 days. Events with magnitudes roughly equivalent to a Richter magnitude of –1.5 were recorded. The amplitude distribution suggests that there was a smaller percentage of small shocks in the Parkfield microaftershock series than has commonly been reported for Japanese and other California aftershock series. b values between 0.8 and 0.9 are commonly reported while the average b value for the Parkfield microaftershock series was 0.59. The distribution of S-P times for the microaftershocks is consistent with the epicentral area defined in other studies as a strip approximately 5 km wide astride a 35 km long trace of the San Andreas fault; however, some evidence suggests that the microaftershock activity extends beyond the zone defined by the larger aftershocks. The spatial distribution of microearthquake activity is shown to be strongly non-uniform within the aftershock zone. The microaftershocks, in general, did not cluster in time about the larger aftershocks (M > 2.0). Of 24 aftershocks with M greater than or equal to 2.0, only one event gave strong evidence of triggering a secondary aftershock series. Assuming that secondary foreshock and/or aftershock series imply the creation or reactivation of a secondary fault, one is led to the conclusion that secondary faulting was a rare occurrence in the Parkfield aftershock zone.

This article has been cited by other articles:

				A. MCGARR Dependence of magnitude statistics on strain rate Bulletin of the Seismological Society of America, February 1, 1976; 66(1): 33 - 44. [Abstract] [PDF]

				G. A. BOLLINGER Historical and recent seismic activity in South Carolina Bulletin of the Seismological Society of America, June 1, 1972; 62(3): 851 - 864. [Abstract] [PDF]