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Static stress drop in the 1994 Northridge, California, aftershock sequence

Hardebeck, Jeanne L. and Hauksson, Egill (1997) Static stress drop in the 1994 Northridge, California, aftershock sequence. Bulletin of the Seismological Society of America, 87 (6). pp. 1495-1501. ISSN 0037-1106.

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We use time-domain pulse widths to estimate static stress drops for 279 M_L 2.5 to 4.0 aftershocks of the 17 January 1994, M_W 6.7 Northridge, California, earthquake. The stress drops obtained range from 0.02 to 40 bars, with a log average of 0.75 bar. Error bars computed for our estimates are typically a factor of 5, indicating that the three order of magnitude scatter in stress drops is not solely a result of measurement errors and that there is a significant amount of heterogeneity in the static stress drops of the aftershocks. Stress drops might be expected to increase with depth, since a fault can maintain a higher shear load at higher confining pressures. We observe an increase in log average stress drop at about 15 km depth, which is statistically significant at the 80% confidence level. The increase is due primarily to a lack of lower stress-drop events below this depth and may be controlled by material properties since the Northridge aftershocks are observed to intersect an anomalously high-velocity body at around this depth (Hauksson and Haase, 1997). An apparent increase in stress drop with magnitude is also observed over the entire magnitude range of the study, although whether this trend is real or an artifact of attenuation of high frequencies in the upper crust is unresolved.

Item Type:Article
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Hauksson, Egill0000-0002-6834-5051
Additional Information:© 1997 by the Seismological Society of America. Manuscript received 1 July 1996. We thank Craig Scrivner and David Wald for their helpful comments on an early draft of the manuscript, and reviewers Mark Zoback and Ruth Harris for their suggestions that helped to refocus and greatly improve the article. We thank Lucy K. Jones for housing the CALB TERRAscope station in her garage. This research was partially supported by USGS Grant 1434-94-G-2440. Contribution Number 5726, Division of Geological and Planetary Sciences, California Institute of Technology. SCEC Contribution Number 337.
Group:Seismological Laboratory
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Other Numbering System NameOther Numbering System ID
Caltech Division of Geological and Planetary Sciences5726
Southern California Earthquake Center (SCEC)337
Issue or Number:6
Record Number:CaltechAUTHORS:20130226-101055259
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Official Citation:Jeanne L. Hardebeck and Egill Hauksson Static stress drop in the 1994 Northridge, California, aftershock sequence Bulletin of the Seismological Society of America, December 1997, v. 87, p. 1495-1501
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:37142
Deposited By: Tony Diaz
Deposited On:26 Feb 2013 19:44
Last Modified:03 Oct 2019 04:44

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