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

Abstract

[1] 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 M w 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.

Aftershocks driven by afterslip and fluid pressure sweeping through a fault‐fracture mesh

“…The northern terminus of the rupture edge coincides with a transition from crystalline and volcanic rocks in the south to unconsolidated sedimentary rocks in the north [Fletcher et al, 2014]. Farther north, in the Yuha Desert, the seismicity delineates a complex network of segmented orthogonal faults [Kroll et al, 2013] (Figure 1). Individual lineations have typical lengths of 2-3 km, are nonplanar, and predominantly dip to the northeast.…”

“…We used continuous seismic data recorded between 4 April 2010 and 26 June 2010 by 112 stations of the Southern California Seismic Network [Southern California Earthquake Data Center, 2013], which includes a temporary deployment of eight stations in the Yuha Desert following EMC [Kroll et al, 2013]. Only shortperiod and broadband seismometers were used.…”

Application of an improved spectral decomposition method to examine earthquake source scaling in Southern California

“…The 2010 M w 7.2 El Mayor‐Cucapah earthquake is the largest event within the footprint of the SCSN during our study period (January 2002 through September 2016). The complex, bilateral faulting of the El Mayor‐Cucapah earthquake [ Wei et al , ; Fletcher et al , ] triggered a dense cloud of aftershocks north of the USA‐Mexico border in the Yuha Desert [ Kroll et al , ; Hauksson et al , ]. Our Yuha Desert study region is composed primarily of these more northerly aftershocks, as the SCSN does not have an adequate azimuthal distribution of station coverage to make reliable spectral estimates for earthquakes to the south of the USA‐Mexico border (Figure ).…”

Delayed Seismicity Rate Changes Controlled by Static Stress Transfer

“…(left) Surface rupture (red; Fletcher et al, ) and triggered surface slip (magenta lines; Rymer et al, ) of the EMC (yellow star and focal mechanism) along with aftershocks and regional seismicity that occurred through December 2010 (Hauksson et al, ). (right) Aftershocks of the EMC in the Yuha Desert region colored by time since the mainshock (Kroll et al, ). The Ocotillo epicenter is shown by the focal mechanism.…”