scholarly journals Characterization of the San Jacinto fault zone near Anza, California, by fault zone trapped waves

2001 ◽  
Vol 106 (B12) ◽  
pp. 30671-30688 ◽  
Author(s):  
Yong-Gang Li ◽  
Frank L. Vernon
Keyword(s):  
Fault Zone ◽  
Trapped Waves ◽  
San Jacinto Fault ◽  
San Jacinto Fault Zone

Internal structure of the San Jacinto fault zone at the Ramona Reservation, north of Anza, California, from dense array seismic data

2020 ◽  
Vol 224 (2) ◽  
pp. 1225-1241
Author(s):  
Lei Qin ◽  
Pieter-Ewald Share ◽  
Hongrui Qiu ◽  
Amir A Allam ◽  
Frank L Vernon ◽  
...  
Keyword(s):  
Internal Structure ◽  
Fault Zone ◽  
Seismic Data ◽  
Damage Zone ◽  
Normal Direction ◽  
Bimaterial Interface ◽  
Trapped Waves ◽  
San Jacinto Fault ◽  
Core Damage ◽  
San Jacinto Fault Zone

SUMMARY We image the internal structure of the San Jacinto fault zone (SJFZ) near Anza, California, with seismic data recorded by two dense arrays (RA and RR) from ∼42 000 local and ∼180 teleseismic events occurring between 2012 and 2017. The RA linear array has short aperture (∼470 m long with 12 strong motion sensors) and recorded for the entire analysed time window, whereas the RR is a large three-component nodal array (97 geophones across a ∼2.4 km × 1.4 km area) that operated for about a month in September–October 2016. The SJFZ at the site contains three near-parallel surface traces F1, F2 and F3 from SW to NE that have accommodated several Mw > 6 earthquakes in the past 15 000 yr. Waveform changes in the fault normal direction indicate structural discontinuities that are consistent with the three fault surface traces. Relative slowness from local events and delay time analysis of teleseismic arrivals in the fault normal direction suggest a slower SW side than the NE with a core damage zone between F1 and F2. This core damage zone causes ∼0.05 s delay at stations RR26–31 in the teleseismic P arrivals compared with the SW-most station, and generates both P- and S-type fault zone trapped waves. Inversion of S trapped waves indicates the core damaged structure is ∼100 m wide, ∼4 km deep with a Q value of ∼20 and 40 per cent S-wave velocity reduction compared with bounding rocks. Fault zone head waves observed at stations SW of F3 indicate a local bimaterial interface that separates the locally faster NE block from the broad damage zone in the SW at shallow depth and merges with a deep interface that separates the regionally faster NE block from rocks to the SW with slower velocities at greater depth. The multiscale structural components observed at the site are related to the geological and earthquake rupture history at the site, and provide important information on the preferred NW propagation of earthquake ruptures on the San Jacinto fault.

scholarly journals Basic data features and results from a spatially dense seismic array on the San Jacinto fault zone

2015 ◽  
Vol 202 (1) ◽  
pp. 370-380 ◽  
Author(s):  
Yehuda Ben-Zion ◽  
Frank L. Vernon ◽  
Yaman Ozakin ◽  
Dimitri Zigone ◽  
Zachary E. Ross ◽  
...  
Keyword(s):  
Fault Zone ◽  
Seismic Array ◽  
Basic Data ◽  
San Jacinto Fault ◽  
San Jacinto Fault Zone ◽  
Dense Seismic Array

A re-examination of historic earthquakes in the San Jacinto fault zone, California

1991 ◽  
Vol 81 (6) ◽  
pp. 2289-2309
Author(s):  
Allison L. Bent ◽  
Donald V. Helmberger
Keyword(s):  
Fault Zone ◽  
Source Parameters ◽  
Travel Times ◽  
Considerable Uncertainty ◽  
San Jacinto Fault ◽  
San Jacinto Fault Zone ◽  
Moment Estimates ◽  
The Moment ◽  
Recent Earthquakes ◽  
Historic Earthquakes

Abstract The high level of seismic activity and the potential for large earthquakes in the San Jacinto fault zone, southern California, make it desirable to have accurate locations and source parameters for as many previous events as possible. Prior to the installation of a dense seismic network in this region, earthquakes were located using only a few stations with generally poor azimuthal coverage resulting in considerable uncertainty in the locations. We relocate and obtain moment estimates for historic (pre-WWSSN) earthquakes in the western Imperial Valley by comparing the waveforms and travel times with recent earthquakes in the region. All the events are in the ML 5.5 to 6.5 range. The historic earthquakes of interest occurred in 1937, 1942, and 1954. We use the 1968 Borrego Mountain, 1969 Coyote Mountain, and 1987 Elmore Ranch earthquakes as calibration events. We employ regional and teleseismic data from continuously operating stations, with Pasadena, DeBilt, Berkeley, Ottawa, and St. Louis recording most of the events. The waveforms imply that all the events are almost pure strike-slip events on vertical or near-vertical faults. Approximate values for the strikes were obtained and are within the range of observed strikes for well-studied earthquakes in this region. The earthquakes are relocated by comparing S-P and surface-wave - S travel times of historic events with the presumably well-located recent events. The relocations require only a small change in location for the 1954 event and a larger adjustment in the 1942 epicenter. It also appears that the 1969 earthquake may have been mislocated. The moment estimates are obtained by direct comparison of the maximum amplitudes. The moment estimates imply that the 1968 and not the 1942 earthquake is the largest to have occurred in the region this century. Previous magnitude estimates suggested the 1942 event was larger.

Structural Properties of the San Jacinto Fault Zone at Blackburn Saddle from Seismic Data of a Dense Linear Array

2018 ◽  
Vol 176 (3) ◽  
pp. 1169-1191 ◽  
Author(s):  
Pieter-Ewald Share ◽  
Amir A. Allam ◽  
Yehuda Ben-Zion ◽  
Fan-Chi Lin ◽  
Frank L. Vernon
Keyword(s):  
Structural Properties ◽  
Fault Zone ◽  
Seismic Data ◽  
Linear Array ◽  
San Jacinto Fault ◽  
San Jacinto Fault Zone
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