Depth Distribution of the 2010 El Mayor-Cucapah Earthquake Sequence (M>=4) Determined from Regional Waveform Modeling

Chunquan Yu, Egill Hauksson, Zhongwen Zhan, & Elizabeth S. Cochran

Submitted August 14, 2017, SCEC Contribution #7614, 2017 SCEC Annual Meeting Poster #075

The 2010 Mw 7.2 El Mayor-Cucapah earthquake ruptured bilaterally over a zone of about 120 km in length. The rupture terminates near the US-Mexico international border in the northwest and near the northern tip of the Gulf of California in the southeast, respectively. Tens of thousands of foreshocks/aftershocks have been detected with the Southern California Seismic Network (SCSN) and located using travel-time location methods. However, because most available stations are located in the US side of the international border, the uncertainty of earthquake depth estimates significantly increases to the southeast. To better constrain the depth distribution of the 2010 El Mayor-Cucapah earthquake sequence, which is crucial for both earthquake seismology and seismotectonic studies, we perform regional waveform modeling. We mainly focus on modeling Pn and its depth phases, i.e. pPn and sPn, at relatively high frequency (~1 Hz), since they are most sensitive to the focal depth. We analyzed all M>=4 earthquakes of the El Mayor-Cucapah sequence in 2010, including 3 foreshocks and 118 aftershocks. We picked Pn at distance larger than 2 degree (to avoid contamination from Pg and PmP) and stacked seismic traces in a narrow azimuthal range (to enhance the signal-to-noise ratio). Synthetic waveforms for various focal depths are computed with the frequency-wave number integration method, and are compared with stacked Pn waveforms. Since amplitudes of Pn and its depth phases are modulated by earthquake radiation pattern, we also inverted the focal mechanism using the Cut-and-Paste (CAP) method. Our results show that about half of these events have clear depth phases, thus providing tight constraints on the focal depth. The difference between our focal depths and those in the catalog generally increases southeastward, consistent with the increased uncertainty of the latter. Near the mainshock epicenter, the catalog systematically overestimates the focal depth.

Yu, C., Hauksson, E., Zhan, Z., & Cochran, E. S. (2017, 08). Depth Distribution of the 2010 El Mayor-Cucapah Earthquake Sequence (M>=4) Determined from Regional Waveform Modeling. Poster Presentation at 2017 SCEC Annual Meeting.

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