Article

Superficial simplicity of the 2010 El Mayor-Cucapah earthquake of Baja California in Mexico

Nature Geoscience (Impact Factor: 11.74). 07/2011; 4:615-618. DOI: 10.1038/ngeo1213

ABSTRACT

The geometry of faults is usually thought to be more
complicated at the surface than at depth and to control the
initiation, propagation and arrest of seismic ruptures. The
fault system that runs from southern California into Mexico is a simple strike-slip boundary: the west side of California and Mexico moves northwards with respect to the east. However, the M_w 7.2 2010 El Mayor–Cucapah earthquake on this fault system produced a pattern of seismic waves that indicates a far more complex source than slip on a planar strike-slip fault^7. Here we use geodetic, remote-sensing and seismological data to reconstruct the fault geometry and history of slip during this earthquake. We find that the earthquake produced a straight 120-km-long fault trace that cut through the Cucapah mountain
range and across the Colorado River delta. However, at depth, the fault is made up of two different segments connected by a small extensional fault. Both segments strike N130° E, but dip in opposite directions. The earthquake was initiated on the connecting extensional fault and 15 s later ruptured the two main segments with dominantly strike-slip motion. We show that complexities in the fault geometry at depth explain well the complex pattern of radiated seismic waves. We conclude that the location and detailed characteristics of the earthquake
could not have been anticipated on the basis of observations of surface geology alone.

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    • "For simplicity, we estimate the average horizontal and vertical displacement along a section of fault to calculate total oblique slip for the estimation of moment release. For this model, we use a range of locking depths of 12 2 km (10–14 km) based on the maximum depth of local seismicity (Hauksson et al., 2010; Wei et al., 2011) and apply the standard equation for moment M 0 , which is the product of rupture area, average displacement, and shear rigidity of the crust, assumed to be 3:1 × 10 11 dyn·cm 2 (Hanks and Kanamori, 1979). A 12 km locking depth on a 60°–90° dipping fault yields a fault width of about 12–14 km; and, using the Figure 9 "
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    ABSTRACT: We present the results of intensive field investigations of the scarp associated with the 23 February 1892 earthquake in northern Baja California. Newly recognized additional offsets suggest the rupture was about 58 km in length, twice as long as previous estimates. Slip produced in the 1892 event varied from purely dextral slip near the international border to roughly 1:1 oblique-normal slip farther south along the 2–4-km-deep portion of the Laguna Salada basin. The portion of the 1892 rupture with oblique-normal slip comprises a number of short, poorly organized, and discon-tinuous fault scarps with heights that vary in concert with their strike. Slip was linked farther south to a short, purely normal fault that forms a large releasing bend at the southern termination of the fault zone. Given the distribution of slip along the earthquake and a likely range of locking depths, we conclude the 1892 earthquake was between M w 7.1–7.3 in magnitude, consistent with previous estimates from macroseismic observations. The length of the Laguna Salada fault that ruptured in 1892 also accommodated minor normal sense displacement along much of its length in the recent 2010 M w 7.2 El Mayor–Cucapah earthquake, which guided the remapping effort.
    Full-text · Article · Oct 2015 · Bulletin of the Seismological Society of America
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    • "The focal mechanism was predominantly strike-slip, although the earthquake originated as a normal faulting event. Detailed waveform modeling suggested that the earthquake ruptured on four faults that manifest as a seemingly single fault trace on the ground, showing superficial simplicity (Wei et al., 2011). "
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    ABSTRACT: In this study, we demonstrate an approach for inverting earthquake source parameters based on high-rate global positioning system (GPS) velocity seismograms. The velocity records obtained from single-station GPS velocity solutions with broadcast ephemeris are used directly for earthquake source parameter inversion using the Cut and Paste method, without requiring conversion of the velocity records into displacement records. Taking the El Mayor-Cucapah earthquake as an example, GPS velocity records from 10 stations with reasonable azimuthal coverage provide earthquake source parameters very close to those from the Global centroid moment tensor (Global CMT) solution. In sparse network tests, robust source parameters with acceptable bias can be achieved with as few as three stations. When the number of stations is reduced to two, the bias in rake angle becomes appreciable, but the magnitude and strike estimations are still robust. The results of this study demonstrate that rapid and reliable estimation of earthquake source parameters can be obtained from GPS velocity data. These parameters could be used for early earthquake warning and shake map construction, because such GPS velocity records can be obtained in real time. © 2015, Science China Press and Springer-Verlag Berlin Heidelberg.
    Full-text · Article · Sep 2015 · Science China Earth Science
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    • "The northern Baja California peninsula has active normal and strike-slip faults originating from the transtensional limit between the Pacific and North America plates (Stock et al., 1991). In this limit, separation of the Baja California peninsula from the continental North America plate occurs and continues to the northwest through the right-lateral movement (Fig. 1 inset ) of the San Andreas fault system (Axen and Fletcher, 1998; Suárez-Vidal et al., 2007; Plattner et al., 2007; Suárez-Vidal et al., 2008; Armstrong, 2010; Wei et al., 2011; Oskin et al., 2012). Within our study area (Fig. 1), south of Mexicali Valley, the Cucapah and El Mayor mountain ranges are located northwest of the Gulf Extensional Province (Suárez-Vidal, et al. 2008). "
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    ABSTRACT: In northern Baja California, the two largest regions with different geological characteristics are the granitic Peninsular Ranges of Baja California (PRBC) and the sedimentary environment of the Mexicali Valley (Lomnitz et al., 1970). The boundary of these two regions is the Main Gulf Escarpment (Fig. 1). The northern Baja California peninsula has active normal and strike‐slip faults originating from the transtensional limit between the Pacific and North America plates (Stock et al., 1991).
    Full-text · Article · Jan 2015 · Seismological Research Letters
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