Small Patches of the Cocos Megathrust in Mexico Ruptured by the June 2020 Mw 7.4 La Crucecita, March 2012 Mw 7.4 Ometepec and February 2018 Mw 7.2 Pinotepa Earthquakes
Session: Subduction Processes Along Latin America Subduction Zones I
Type: Oral
Date: 4/19/2021
Presentation Time: 10:15 AM Pacific
Description:
Three earthquakes with Mw 7.2 to 7.4 have ruptured the megathrust beneath Oaxaca in the last 9 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 epicenters 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 on the megathrust.
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. Analysis of La Crucecita indicates rupture over slightly larger 20 by 40 km area. The earthquakes ruptured small areas in 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. Limited extent of these ruptures may leave large shallower portions of the megathrust locked and loaded.
Presenting Author: Eric J. Fielding
Student Presenter: No
Authors
Eric Fielding Presenting Author Corresponding Author eric.j.fielding@jpl.nasa.gov Caltech |
Romain Jolivet romain.jolivet@ens.fr École Normale Supérieure |
Baptiste Gombert baptiste.gombert@gmail.com Collect Localisation Satellites |
Alejandro González-Ortega aglez@cicese.mx CICESE |
Zacharie Duputel zacharie.duputel@unistra.fr Université de Strasbourg |
Cunren Liang cunrenl@caltech.edu Caltech |
David Bekaert David.Bekaert@jpl.nasa.gov Caltech |
Sergey Samsonov sergey.samsonov@canada.ca CCMEO |
Sarah Minson sminson@usgs.gov U.S. Geological Survey |
Jeremy Maurer jmaurer@mst.edu Missouri S&T, Rolla, Missouri, United States |
Jean-Paul Ampuero ampuero@geoazur.unice.fr Université Côte d’Azur, Géoazur, Nice, , France |
Small Patches of the Cocos Megathrust in Mexico Ruptured by the June 2020 Mw 7.4 La Crucecita, March 2012 Mw 7.4 Ometepec and February 2018 Mw 7.2 Pinotepa Earthquakes
Category
Subduction Processes Along Latin America Subduction Zones