Probing the structure of the flat subduction in Oaxaca, Mexico, using a temporal seismic array.

Cocos plate assumes a peculiar flat subduction beneath Mexico. Oaxaca region is the part of Mexico where the trench is closest to the coastline and where a transition from flat to a more dipping subduction plane occurs.

The closest seismic broadband seismometers existing near the coast are managed by the Mexican National Seismological Service (SSN) and consist of three stations installed over a straight coastline of Oaxaca of more than 200 km. The limited number of stations makes it very      difficult to get a detailed study of the seismicity able to provide sufficient information to characterize the events of magnitude less than 4.0-4.5 in this portion of the subduction.

In this work we show the preliminary results of a temporary network of 11 stations (9 broadband and 2 Raspberry Shakes) installed since September 2021 on the Oaxaca coast and designed to complement the coverage of the SSN stations. The two networks are now able to provide enough information to obtain refined catalogs and carry out studies that can probe the structure of the crust and upper mantle of the region with unprecedented detail.

In particular we will show the first results of the refined event locations, focal mechanisms and 3D seismic velocity models. All this information is lighting several features unknown of this portion of the Cocos plate and the overlaying North America one, opening new questions about the tectonics and geodynamics of the region.

Work supported by the PASPA-DGAPA, UNAM program, as a sabbatical year at Universidad del Mar (UMAR), Puerto Angel, by the PAPIIT-DGAPA project: IN108221, and by the internal project of the UMAR: 2II2003 and PRODEP UMAR-PTC-181.