Aftershocks of the 2010 Mw 7.2 El Mayor-Cucapah earthquake reveal complex faulting in the Yuha Desert, California

• Published in: Journal of geophysical research. Solid earth 2013-12, Vol.118 (12), p.6146-6164
• Main Authors: Kroll, Kayla A., Cochran, Elizabeth S., Richards-Dinger, Keith B., Sumy, Danielle F.
• Format: Article
• Language: English
• Subjects: aftershock relocation; Aftershocks; conjugate faulting; Deserts; Dimensional analysis; Earth sciences; Earth, ocean, space; Earthquakes; El Mayor-Cucapah; Exact sciences and technology; Fault lines; Geophysics; hypoDD; Hypoinverse; Hypoinverse, Velest, hypoDD; Plate tectonics; Relocation; Seismic activity; seismicity rates; Seismology; spatio-temporal migration of aftershocks; Velest
• ISSN: 2169-9313; 2169-9356
• DOI: 10.1002/2013JB010529

We detect and precisely locate over 9500 aftershocks that occurred in the Yuha Desert region during a 2 month period following the 4 April 2010 Mw 7.2 El Mayor‐Cucapah (EMC) earthquake. Events are relocated using a series of absolute and relative relocation procedures that include Hypoinverse, Velest, and hypoDD. Location errors are reduced to ∼40 m horizontally and ∼120 m vertically. Aftershock locations reveal a complex pattern of faulting with en echelon fault segments trending toward the northwest, approximately parallel to the North American‐Pacific plate boundary and en echelon, conjugate features trending to the northeast. The relocated seismicity is highly correlated with published surface mapping of faults that experienced triggered surface slip in response to the EMC main shock. Aftershocks occurred between 2 km and 11 km depths, consistent with previous studies of seismogenic thickness in the region. Three‐dimensional analysis reveals individual and intersecting fault planes that are limited in their along‐strike length. These fault planes remain distinct structures at depth, indicative of conjugate faulting, and do not appear to coalesce onto a throughgoing fault segment. We observe a complex spatiotemporal migration of aftershocks, with seismicity that jumps between individual fault segments that are active for only a few days to weeks. Aftershock rates are roughly consistent with the expected earthquake production rates of Dieterich (1994). The conjugate pattern of faulting and nonuniform aftershock migration patterns suggest that strain in the Yuha Desert is being accommodated in a complex manner. Key Points Relocated seismicity reveals conjugate faulting in the Yuha Desert Spatio‐temporal relationships suggest individual faults are only active briefly Aftershock rates generally fit those described by rate‐and‐state friction