Insights into the complexities of a seismogenic subduction zone: Analysis of a high-quality aftershock data set from the 2017 Tehuantepec (M8.2) offshore Mexico earthquake

Subduction zones – where one tectonic plate dives beneath another – are responsible for the most impactful natural hazards on the planet. Those include large earthquakes, tsunamis, and volcanic eruptions which at times are explosive. These destructive events present major threats to human societies.

They often cause human casualties and economic losses. The Mexican subduction zone has been responsible for large, devasting earthquakes throughout the past century. It is marked by the Middle American Trench off the coast of Mexico.

There, the Cocos Plate dives beneath the continental North American Plate. It was responsible for the September 7, 2017 Tehuantepec, Mexico earthquake of magnitude 8.2 on the Richter scale. Here, the researchers investigate what caused this destructive event.

They use data collected by a rapid seismic-array deployment following the earthquake. Analyzing the high-resolution data, they gradually unveil subduction-zone processes and earthquake mechanisms. This project leverages an international partnership between the University of Texas at El Paso (UTEP) and several institutions in Mexico.

It also provides training for graduate and undergraduate students, notably from groups underrepresented in science.

Here the team analyze a high-quality, unique aftershock dataset from the 2017 Tehuantepec earthquake. The data were collected after a seismic deployment supported by a RAPID award. The RAPID network augmented permanent and temporary networks deployed by the Universidad Nacional Autónoma de Mexico (UNAM).

It included ten broadband instruments deployed in early Oct. 2017 (that recorded data for 6 months) and 51 UTEP-owned Nodes (5-Hz, 3-component geophones, active for 22 days). During the broadband deployment, the Servicio Sismológico Nacional (SSN) recorded over 30,000 aftershocks. This highlights the robust nature of earthquake generation.

The project goal is to answer fundamental and specific questions that relate to subduction zone processes. Fundamental questions, determined by community efforts, include: when and where do large earthquakes happen? How do spatial variations in subduction inputs affect seismicity and magmatism?

How are surface processes linked to subduction? Specific questions about the Mexican subduction zone are: will the Tehuantepec earthquake load the upper plate and possibly trigger a large earthquake on the plate interface? Are the Tehuantepec and subsequent earthquakes linked?

These earthquakes are the September 19, 2017 Morelos-Puebla, Mexico (M7.1), the February 18, 2018 Pinotepa Nacional, Mexico (M7.2), and the June 23, 2020 (M7.4) La Crucecita. To answer these questions, the researchers merge the various datasets which builds a foundation for five complementary approaches: 1) calculate a high-resolution aftershock dataset; 2) analyze seismicity and stress, 3) search for earthquake triggering mechanisms, 4) define the structure of the subduction zone, and 5) integrate results to address remaining questions.

This project strengthens a strong collaboration between UTEP and, in Mexico, UNAM, the SSN, and the Universidad Autónoma de Ciudad Juárez.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.