Complex active faults and seismicity rates in the trifurcation area of the San Jacinto fault zone illuminated by aftershocks of the 2016 Mw 5.2 Borrego Springs earthquake

Zachary E. Ross, Egill Hauksson, & Yehuda Ben-Zion

Published August 14, 2016, SCEC Contribution #6776, 2016 SCEC Annual Meeting Poster #218

We summarize spatial properties and rates of early aftershocks of the Mw 5.2, June 2016, Borrego Springs earthquake and background seismicity in the trifurcation area of the San Jacinto Fault Zone. In this area, the fault zone splits into three primary sub-parallel strands and is associated with broad Vp/Vs anomalies. A template matching technique is used to detect and locate more than 25,000 early aftershocks that illuminate highly complex active fault structures, in conjunction with high-resolution regional seismicity. The hypocenters form lineations of seismicity both along strike and normal to the main structure, various dipping streaks of seismicity, coincident with interlaced strike-slip and normal faults at depth. Events larger than M > 4 are located on the three main faults, while much of the small magnitude aftershocks occurred in a damage zone between the Clark and Buck Ridge strands, which spans several kilometers. This spatial separation of events in different magnitude ranges also is manifested in bimodal frequency-magnitude distributions of events close to and away from the main faults. The results provide important constraints on the physics of faulting at depth.

Citation
Ross, Z. E., Hauksson, E., & Ben-Zion, Y. (2016, 08). Complex active faults and seismicity rates in the trifurcation area of the San Jacinto fault zone illuminated by aftershocks of the 2016 Mw 5.2 Borrego Springs earthquake. Poster Presentation at 2016 SCEC Annual Meeting.

Related Projects & Working Groups
Seismology