T053-0022
The June 2020 Mw 7.4 La Crucecita, March 2012 Mw 7.4 Ometepec and February 2018 Mw 7.2 Pinotepa Earthquakes in Mexico Ruptured Small Patches of the Cocos Megathrust
Wednesday, 16 December 2020
Poster
Eric Jameson Fielding, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, United States, Baptiste Gombert, Institut de Physique du Globe de Strasbourg, Strasbourg, France, Alejandro Gonzalez-Ortega, Center for Scientific Research and Higher Education at Ensenada, Ensenada, Mexico, Zacharie Duputel, California Institute of Technology, Pasadena, United States, Cunren Liang, California Institute of Technology, Pasadena, CA, United States, David P Bekaert, JPL/NASA/Caltech, Pasadena, CA, United States, Sergey V Samsonov, Canada Centre for Remote Sensi, Ottawa, ON, Canada, Romain Jolivet, Ecole Normale Supérieure, PSL Research University, CNRS UMR 8538, Laboratoire de Géologie, Paris, France, Jeremy Maurer, Indiana University, Bloomington, IN, United States and Jean-Paul Ampuero, Université Côte d’Azur, CNRS, Observatoire de la Côte d’Azur, IRD, Géoazur, Valbonne, France
Abstract:
Three earthquakes with Mw 7.2 to 7.4 have ruptured the megathrust beneath Oaxaca in the last 8 years. The megathrust of the Cocos Plate beneath Southern Mexico has major variations in the geometry and behavior. The segment beneath the Mexican state of Oaxaca has relatively frequent magnitude 7–7.5 earthquakes on the shallow part of the megathrust and within the subducting slab, and it also has large aseismic slow-slip events. The recent magnitude 7+ megathrust events in 2012, 2018, and 2020 have been at similar depths between 20 and 25 km near the up-dip edge of the slow-slip zone. We study the ruptures of the 20 March 2012 Mw 7.4 Ometepec earthquake near the Guerrero-Oaxaca border, the16 February 2018 Mw 7.2 Pinotepa earthquake near Pinotepa Nacional in Oaxaca, and the 23 June 2020 Mw 7.4 La Crucecita earthquake beneath southeast Oaxaca that were all megathrust events. The 2012 Ometepec and 2018 Pinotepa earthquake epicenters were located about 45 km apart by the Mexican Servicio Sismológico Nacional (SSN), with the 2020 La Crucecita epicenter about 210 km further east.
We use geodetic measurements from interferometric analysis of synthetic aperture radar (InSAR) and GNSS coseismic offsets to estimate finite-fault slip models for all three earthquakes. We analyzed InSAR data from Copernicus Sentinel-1A and -1B satellites and JAXA ALOS-2 satellite for 2018 Pinotepa and 2020 La Crucecita and Canadian RADARSAT-2 for 2012 Ometepec. Our Bayesian (AlTar) static slip models for the Pinotepa and Ometepec earthquakes shows all of the slip confined to very small (10-20 km diameter) ruptures, similar to some early seismic waveform fits, and the two ruptures do not overlap. Preliminary analysis of La Crucecita indicates a similar area. The earthquakes ruptured part of the Cocos megathrust that has been previously mapped as partially coupled; at least small asperities in that zone of the subduction interface are fully coupled and fail in high stress-drop earthquakes. Preliminary analysis of GNSS data after the Pinotepa earthquake indicates rapid afterslip on the megathrust in the region of coseismic slip. Previous analysis by Graham et al. (2014) and others showed afterslip after the 2012 Ometepec event, largely down-dip. This part of the megathrust may have areas of low coupling that have afterslip or slow slip between the locked patches.
