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Properties of the Aftershock Sequence of the 1999 M_w 7.1 Hector Mine Earthquake: Implications for Aftershock Hazard

Wiemer, Stefan and Gerstenberger, Matt and Hauksson, Egill (2002) Properties of the Aftershock Sequence of the 1999 M_w 7.1 Hector Mine Earthquake: Implications for Aftershock Hazard. Bulletin of the Seismological Society of America, 92 (4). pp. 1227-1240. ISSN 0037-1106. doi:10.1785/0120000914.

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We investigate the spatial and temporal seismicity parameters and the related probabilistic aftershock hazard for the aftershock sequence of the 1999 M_w 7.1 Hector Mine mainshock and compare it with the neighboring 1992 M_w 7.3 Landers sequence. Using a catalog of 11,000 earthquakes, we determine the earthquake size distribution (b-value), the aftershock decay rate (p-value), and the seismic activity rate (a-value). The b-values are high (b > 1.2) within the rupture area, significantly lower (b ≈ 0.7) north of the rupture area, and increase with time since the mainshock. Probabilistic aftershock hazard maps, computed automatically as early as 4 days after the mainshock, identified the northernmost part of the sequence as the highest-hazard region. These maps show a good agreement between the forecasts and the recorded large aftershocks. Based on the asymmetrical b-value and hazard patterns for both the Hector Mine and Landers sequences, we hypothesize that the mainshock rupture directivity and slip distribution influence aftershock hazard. Current static or dynamic stress triggering models cannot resolve this spatial and temporal evolution of the hazard. Stress tensor inversions of 1400 relocated first-motion focal mechanisms show predominantly a strike-slip stress state with a SW–NE trend of the greatest principal stress. The heterogeneity of the stress field is unusually high near the Hector Mine and Landers mainshock ruptures, particularly near patches of large slip.

Item Type:Article
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Hauksson, Egill0000-0002-6834-5051
Additional Information:© 2002 by the Seismological Society of America. Manuscript received 23 October 2000. The author would like to thank M. Wyss, W. Arabasz, V. Langenheim, and an anonymous reviewer for comments and suggestions that greatly helped to improve the manuscript, and to A. Michael for providing stress tensor inversion software and advice. This research was supported by the Southern California Earthquake Center. SCEC is funded by NSF Cooperative Agreement EAR-8920136 and USGS Cooperative Agreements 14-08-0001-A0899 and 1434-HQ-97AG01718. The SCEC contribution number for this paper is 543. This article is Contribution Number 1202 of the Geophysical Institute, ETH Zurich, and Contribution Number 8742 of Caltech, Division of Geology and Planetary Science.
Group:Seismological Laboratory
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Southern California Earthquake Center (SCEC)UNSPECIFIED
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Other Numbering System NameOther Numbering System ID
Southern California Earthquake Center (SCEC)543
ETH Zurich Geophysical Institute1202
Caltech Division of Geology and Planetary Sciences8742
Issue or Number:4
Record Number:CaltechAUTHORS:20130226-104808990
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Official Citation:Stefan Wiemer, Matt Gerstenberger, and Egill Hauksson Properties of the Aftershock Sequence of the 1999 Mw 7.1 Hector Mine Earthquake: Implications for Aftershock Hazard Bulletin of the Seismological Society of America, May 2002, v. 92, p. 1227-1240, doi:10.1785/0120000914
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:37146
Deposited By: Tony Diaz
Deposited On:26 Feb 2013 20:12
Last Modified:09 Nov 2021 23:27

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