HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Figures Only Full Text Full Text (PDF) Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (11) Citing Articles via Google Scholar Google Scholar Articles by Anooshehpoor, A. Articles by Brune, J. N. Search for Related Content GeoRef GeoRef Citation

Quasi-Static Slip-Rate Shielding by Locked and Creeping Zones as an Explanation for Small Repeating Earthquakes at Parkfield

Seismological Laboratory, 174
Mackay School of Mines
University of Nevada, Reno Reno,
Nevada 89557-0141

In a recent study of microearthquakes along the Parkfield segment of the San Andreas fault, Nadeau et al. (1995) have found that much of the seismicity in the region is characterized by quasi-periodic repeating sequences of small earthquakes that are essentially identical in waveform, size and, location. Nadeau and Johnson (1998) interpreted these as repeated slip on a given asperity driven by a steady slip rate of 2.3 cm/yr and concluded that the stress drops needed to be extremely high, of the order of 20 kilobars. We propose another explanation for these small repeating events, namely that an inner asperity is surrounded by a larger creeping zone, which in turn is surrounded by a still larger locked zone. This geometry produces a local slip velocity much less than the overall creep velocity observed on a still larger scale (slip velocity shielding). We have constructed a foam rubber model to illustrate the phenomenon. The time sequences of small events at the asperity, punctuated by large events which rupture the whole block, look very similar to the cumulative moment plots of Nadeau and Johnson. The actual dynamic stress drops are of the same order as for the large events. Thus the results of the model correspond to the observations of Nadeau and Johnson and suggest that the model may be appropriate to explain their observations, without requiring super strong asperities.

This article has been cited by other articles:

				D. C. Templeton, R. M. Nadeau, and R. Burgmann Behavior of Repeating Earthquake Sequences in Central California and the Implications for Subsurface Fault Creep Bulletin of the Seismological Society of America, February 1, 2008; 98(1): 52 - 65. [Abstract] [Full Text] [PDF]

				L. R. Johnson and R. M. Nadeau Asperity Model of an Earthquake: Dynamic Problem Bulletin of the Seismological Society of America, February 1, 2005; 95(1): 75 - 108. [Abstract] [Full Text] [PDF]

				Asperity Models for Earthquakes Bulletin of the Seismological Society of America, August 1, 2003; 93(4): 1792 - 1802.

				Asperity Model of an Earthquake: Static Problem Bulletin of the Seismological Society of America, March 1, 2002; 92(2): 672 - 686.

				A Simple Stick-Slip and Creep-Slip Model for Repeating Earthquakes and its Implication for Microearthquakes at Parkfield Bulletin of the Seismological Society of America, December 1, 2001; 91(6): 1797 - 1804.