Rapid finite-fault analysis of large Mexico earthquakes using teleseismic P waves

We propose a rapid, finite-fault inversion procedure to derive first-order estimates of the coseismic slip following large Mw > 7 earthquakes in Mexico using teleseismic P waves obtained in near real time. The procedure uses kinematic fault parameters and waveform properties prescribed based on the magnitude of the event. Two consecutive inversions are performed, one for each of the two nodal planes in the earthquake source mechanism, allowing an automated analysis of the P-wave dataset with minimal manual intervention. Following the inversion process, the appropriate slip model is selected based on seismotectonic considerations in the earthquake source region. The inversion procedure was applied to the Mw 7 Acapulco subduction earthquake of 8 September 2021 using the source parameters posted online by the U.S. Geological Survey (USGS), resulting in the derivation of a preliminary, first-order source model within 1 h after the event. The slip model shows a single source region similar to the rupture area observed by the USGS using body- and surface-wave records. We also conducted a rapid analysis of the teleseismic P waves available for the Mw 8.2 normal-faulting Chiapas earthquake of 8 September 2017 and recovered a slip model comparable to the finite-fault model obtained by the USGS for that event. For both earthquakes, the time required for waveform retrieval and analysis was less than 5 min, indicating that the procedure can be used to derive timely, preliminary slip models for large Mexico events that would be useful for earthquake early alerting and post-earthquake response.