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

Journal Article · · Geophysical Journal International
DOI:https://doi.org/10.1093/gji/ggx191· OSTI ID:1535649
 [1];  [2];  [3];  [2];  [4]
  1. Univ. of Southern California, Los Angeles, CA (United States); DOE/OSTI
  2. Univ. of Southern California, Los Angeles, CA (United States)
  3. California Inst. of Technology (CalTech), Pasadena, CA (United States)
  4. Univ. of California, San Diego, CA (United States)
+ Show Author Affiliations
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.
Research Organization:
Univ. of California, San Diego, CA (United States); Univ. of Southern California, Los Angeles, CA (United States)
Sponsoring Organization:
USDOE Office of Science (SC)
Grant/Contract Number:
SC0016520; SC0016527
OSTI ID:
1535649
Journal Information:
Geophysical Journal International, Journal Name: Geophysical Journal International Journal Issue: 2 Vol. 210; ISSN 0956-540X
Publisher:
Oxford University PressCopyright Statement
Country of Publication:
United States
Language:
English

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Cited By (7)

Structural Properties of the San Jacinto Fault Zone at Blackburn Saddle from Seismic Data of a Dense Linear Array journal September 2018
Seismic Imaging of the Southern California Plate Boundary around the South-Central Transverse Ranges Using Double-Difference Tomography journal November 2018
Imaging the Fault Damage Zone of the San Jacinto Fault Near Anza With Ambient Noise Tomography Using a Dense Nodal Array journal November 2019
A Detailed Earthquake Catalog for the San Jacinto Fault‐Zone Region in Southern California journal July 2019
Eikonal Tomography of the Southern California Plate Boundary Region journal September 2019
Wave equation dispersion inversion of surface waves recorded on irregular topography journal January 2019
Imaging subsurface structures in the San Jacinto fault zone with high-frequency noise recorded by dense linear arrays journal February 2019

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