The 2010 M w 7.2 El Mayor-Cucapah Earthquake Sequence, Baja California, Mexico and Southernmost California, USA: Active Seismotectonics along the Mexican Pacific Margin

Abstract

The El Mayor-Cucapah earthquake sequence started with a few foreshocks in March 2010, and a second sequence of 15 foreshocks of M [ 2 (up to M4.4) that occurred during the 24 h preceding the mainshock. The foreshocks occurred along a northsouth trend near the mainshock epicenter. The M w 7.2 mainshock on April 4 exhibited complex faulting, possibly starting with a *M6 normal faulting event, followed *15 s later by the main event, which included simultaneous normal and right-lateral strikeslip faulting. The aftershock zone extends for 120 km from the south end of the Elsinore fault zone north of the US-Mexico border almost to the northern tip of the Gulf of California. The waveformrelocated aftershocks form two abutting clusters, each about 50 km long, as well as a 10 km north-south aftershock zone just north of the epicenter of the mainshock. Even though the Baja California data are included, the magnitude of completeness and the hypocentral errors increase gradually with distance south of the international border. The spatial distribution of large aftershocks is asymmetric with five M5? aftershocks located to the south of the mainshock, and only one M5.7 aftershock, but numerous smaller aftershocks to the north. Further, the northwest aftershock cluster exhibits complex faulting on both northwest and northeast planes. Thus, the aftershocks also express a complex pattern of stress release along strike. The overall rate of decay of the aftershocks is similar to the rate of decay of a generic California aftershock sequence. In addition, some triggered seismicity was recorded along the Elsinore and San Jacinto faults to the north, but significant northward migration of aftershocks has not occurred. The synthesis of the El Mayor-Cucapah sequence reveals transtensional regional tectonics, including the westward growth of the Mexicali Valley and the transfer of Pacific-North America plate motion from the Gulf of California in the south into the southernmost San Andreas fault system to the north. We propose that the location of the 2010 El Mayor-Cucapah, as well as the 1992 Landers and 1999 Hector Mine earthquakes, may have been controlled by the bends in the plate boundary.

Uniform California Earthquake Rupture Forecast, Version 3 (UCERF3)--The Time-Independent Model

“…For example, it is not clear whether the 2010 El Mayor-Cucapah earthquake (Hauksson et al, 2011) was an event on the UCERF2 Laguna Salada fault source or whether it was part of the gridded/background seismicity Figure 3. UCERF3 long-term model logic-tree branches with weights given in parentheses.…”

“…The most salient of these were (1) to relax segmentation assumptions and include multifault ruptures and (2) to incorporate spatiotemporal clustering for the timedependent forecasting of aftershocks and other triggered earthquake sequences. Both of these issues were subsequently, and dramatically, exemplified following the UCERF2 publication, by events such as the 2011 M 9 Tohoku earthquake with respect to segmentation (e.g., Kagan and Jackson, 2013), the 2011 M 6.3 Christchurch earthquake in terms of spatiotemporal clustering (e.g., Kaiser et al, 2012), and both the 2010 M 7.2 El Mayor-Cucapah and 2012 M 8.6 Sumatra earthquakes in regard to multifault ruptures (e.g., Hauksson et al, 2011;Meng et al, 2012). There is also now a substantial body of literature on the viability of multifault ruptures (e.g., Segall and Pollard, 1980;Knuepfer, 1989;Harris et al, 1991;Harris and Day, 1993;Lettis et al, 2002;Duan and Oglesby, 2006;Wesnousky, 2006;Shaw and Dieterich, 2007;Black and Jackson, 2008;and Finzi and Langer, 2012).…”

Geologic and structural controls on rupture zone fabric: A field-based study of the 2010 Mw 7.2 El Mayor-Cucapah earthquake surface rupture

“…1; Wei et al, 2011;Rymer et al, 2011;Oskin et al, 2012;Fletcher et al, 2014). The rupture sequence initiated near the center of the surface rupture zone and propagated bilaterally to the northwest and southeast (Hauksson et al, 2010;Wei et al, 2011;Uchide et al, 2013;Fletcher et al, 2014). Southeast of the epicenter, primary slip occurred on a southwest-dipping fault beneath the fluid-saturated sediments of the Colorado River delta, and surface faulting was largely masked by coseismically induced liquefaction and lateral spreading features ( Fig.…”

Holocene paleo-earthquakes recorded at the transfer zone of two major faults: The Pastores and Venta de Bravo faults (Trans-Mexican Volcanic Belt)

“…Faulting along a complex fault zone involving neighboring faults and fault segments has been shown to be common in different tectonic settings, especially those occurring at extensional or transtensional regimes (e.g., Beanland et al, 1989;Berryman et al, 2008;Hauksson et al, 2011;Fletcher et al, 2014). In the Acambay graben, and according to the descriptions of Urbina and Camacho (1913), multiple faults ruptured during the Acambay earthquake.…”