Internal structure of the San Jacinto fault zone in the trifurcation area southeast of Anza, California, from data of dense linear arrays

Lei Qin, Yehuda Ben-Zion, Hongrui Qiu, Pieter-Ewald Share, Zachary E. Ross, & Frank L. Vernon

Submitted August 14, 2016, SCEC Contribution #6784, 2016 SCEC Annual Meeting Poster #220

We analyze two years of data from a linear array composed of six 3-component sensors separated by about 25 m, and one-month data from 1108 vertical geophones in ~650 m x 650 m box configuration with instrument spacing 10-30 m, straddling the Clark branch of the San Jacinto fault zone southeast of Anza, California. The examined data include recordings from >10000 local events and some teleseismic events. Automatic picking algorithms and visual inspection are used to identify P and S body waves, along with fault zone head and trapped waves. The locations of the seismogenic fault and damage zone are found by examining waveform changes in both along-strike fault-normal directions. The seismogenic fault location agrees with a geologically mapped surface trace of the Clark branch. Regional earthquake tomography shows that the NE side of the fault has faster seismic velocity on large scale. Statistical analysis of P arrival times indicates a local reversal of the velocity contrast across the fault, with slower velocities NE of the fault related to the fault damage zone. A portion of the damage zone generates P trapped waves. Waveforms recorded by several fault-normal lines of the box array are stacked to improve the ability to detect fault zone head and S trapped waves. Updated results will be presented in the meeting.

Citation
Qin, L., Ben-Zion, Y., Qiu, H., Share, P., Ross, Z. E., & Vernon, F. L. (2016, 08). Internal structure of the San Jacinto fault zone in the trifurcation area southeast of Anza, California, from data of dense linear arrays. Poster Presentation at 2016 SCEC Annual Meeting.


Related Projects & Working Groups
Seismology