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Internal structure of the San Jacinto fault zone at Blackburn Saddle from seismic data of a linear array

Share, Pieter-Ewald and Ben-Zion, Yehuda and Ross, Zachary E. and Qiu, Hongrui and Vernon, Frank L. (2017) Internal structure of the San Jacinto fault zone at Blackburn Saddle from seismic data of a linear array. Geophysical Journal International, 210 (2). pp. 819-832. ISSN 0956-540X. doi:10.1093/gji/ggx191.

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Local and teleseismic earthquake waveforms recorded by a 180-m-long linear array (BB) with seven seismometers crossing the Clark fault of the San Jacinto fault zone northwest of Anza are used to image a deep bimaterial interface and core damage structure of the fault. Delay times of P waves across the array indicate an increase in slowness from the southwest most (BB01) to the northeast most (BB07) station. Automatic algorithms combined with visual inspection and additional analyses are used to identify local events generating fault zone head and trapped waves. The observed fault zone head waves imply that the Clark fault in the area is a sharp bimaterial interface, with lower seismic velocity on the southwest side. The moveout between the head and direct P arrivals for events within ∼40 km epicentral distance indicates an average velocity contrast across the fault over that section and the top 20 km of 3.2 per cent. A constant moveout for events beyond ∼40 km to the southeast is due to off-fault locations of these events or because the imaged deep bimaterial interface is discontinuous or ends at that distance. The lack of head waves from events beyond ∼20 km to the northwest is associated with structural complexity near the Hemet stepover. Events located in a broad region generate fault zone trapped waves at stations BB04–BB07. Waveform inversions indicate that the most likely parameters of the trapping structure are width of ∼200 m, S velocity reduction of 30–40 per cent with respect to the bounding blocks, Q value of 10–20 and depth of ∼3.5 km. The trapping structure and zone with largest slowness are on the northeast side of the fault. The observed sense of velocity contrast and asymmetric damage across the fault suggest preferred rupture direction of earthquakes to the northwest. This inference is consistent with results of other geological and seismological studies.

Item Type:Article
Related URLs:
URLURL TypeDescription
Ben-Zion, Yehuda0000-0002-9602-2014
Ross, Zachary E.0000-0002-6343-8400
Qiu, Hongrui0000-0002-4219-0039
Additional Information:© 2017 The Authors. Published by Oxford University Press on behalf of The Royal Astronomical Society. Received: 03 February 2017; Revision Received: 29 April 2017; Accepted: 04 May 2017; Published: 05 May 2017. The study was supported by the National Science Foundation (grant EAR-1620601) and the U.S. Department of Energy (awards DE-SC0016520 and DE-SC0016527). The seismic instruments were provided by the Incorporated Research Institutions for Seismology (IRIS) through the PASSCAL Instrument Center at New Mexico Tech. Data collected are available through the IRIS Data Management Center. The facilities of the IRIS Consortium are supported by the National Science Foundation under Cooperative Agreement EAR-1261681 and the DOE National Nuclear Security Administration. The manuscript benefitted from comments by two anonymous referees.
Group:Seismological Laboratory
Funding AgencyGrant Number
Department of Energy (DOE)DE-SC0016520
Department of Energy (DOE)DE-SC0016527
Subject Keywords:Earthquake dynamics; Body waves; Interface waves; Guided waves; Rheology and friction of fault zones; Continental tectonics: strike-slip and transform
Issue or Number:2
Record Number:CaltechAUTHORS:20170921-100722609
Persistent URL:
Official Citation:Pieter-Ewald Share, Yehuda Ben-Zion, Zachary E. Ross, Hongrui Qiu, Frank L. Vernon; Internal structure of the San Jacinto fault zone at Blackburn Saddle from seismic data of a linear array, Geophysical Journal International, Volume 210, Issue 2, 1 August 2017, Pages 819–832,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:81670
Deposited By: Tony Diaz
Deposited On:21 Sep 2017 17:35
Last Modified:15 Nov 2021 19:45

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