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Investigation of the Yorba Linda Trend using earthquake relocation based on waveform cross-correlation

Kyle P. Macy, & Jascha Polet

Published August 14, 2019, SCEC Contribution #9670, 2019 SCEC Annual Meeting Poster #067

The Yorba Linda Trend was defined in the early 1990s as a southwest trending series of earthquakes that starts near the center of the Chino Hills, transects the Whittier Fault and extends into the southeastern Los Angeles Basin. The Trend incorporates a series of individual earthquake sequences, now including the 2008 Chino Hills earthquake sequence, and the 2002 and 2012 Yorba Linda earthquakes, which occurred just northeast of the Whittier Fault. The earthquakes in the La Habra Sequence exhibit a similar trend and are located just to the west of the Trend, extending from the Whittier Fault towards the Coyote Hills Fault System. Many of the events in this area are characterized by a strike slip mechanism, but the fault plane of most events is unclear.

We used waveform data from the Southern California Earthquake Data Center for all events in this area from 1989 to 2018. By implementing the GISMO cross correlation MATLAB toolbox and Growclust relocation algorithm, we were able to successfully relocate approximately 64% of these earthquakes. We used P and S-wave arrival times from 31 close-in permanent network stations and numerous 1-D velocity models associated with the area. Preliminary results show a tighter series of clusters. Two clusters of Mw 5.1 La Habra aftershocks appear to be relocated near the furthest extents of the La Habra Sequence, with the southwest cluster situated around the Coyote Hills Faults. The 2002 and 2012 Yorba Linda earthquakes reveal a short northeast-southwest trending series of events situated just north of the surface expression of the Whittier Fault. The aftershock sequence associated with the 2008 Mw 5.4 Chino Hills earthquake appears more scattered, with most events occurring at shallower depths than the mainshock. After earthquake relocation, we do not see a clear linear trend of events that would correspond to the Yorba Linda Trend, as it was defined in the early 1990s.

We are currently in the process of implementing the Bayesloc3 relocation code that utilizes the Markov-Chain Monte Carlo method. Earthquake locations from the Bayesloc3 relocation algorithm will be compared to our Growclust results.

Key Words
Los Angeles Basin, Tectonics, Earthquake Relocation, Chino Hills, Earthquake Trends, Seismotectonics

Macy, K. P., & Polet, J. (2019, 08). Investigation of the Yorba Linda Trend using earthquake relocation based on waveform cross-correlation. Poster Presentation at 2019 SCEC Annual Meeting.

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