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The 2017 Mw 8.2 Mexican Earthquake Jumped From a Normal Outer-rise Fault Onto the Megathrust Interface

Description: 

The 2017 Mw 8.2 Tehuantepec earthquake was the largest normal-faulting earthquake ever recorded in Mexico. It occurred offshore on a reactivated outer-rise fault within the Tehuantepec seismic gap, a tectonically complex region within the intersection of the North American, Caribbean, and Cocos plates. Prior to 2017, the Tehuantepec segment was considered a seismic gap, having produced no large megathrust earthquakes for over a century. Previous studies showed that the rupture initiated approximately 100 km offshore, propagated northwestward for ~60 km into the plate boundary zone, then jumped ~10 km inland as it crossed the trench-perpendicular Tehuantepec Ridge before continuing another ~60 km and terminating abruptly.

Using a machine-learning-based earthquake-detection workflow applied to data from a temporary seismic array and permanent Mexican stations, Garcia et al. (2025) produced a high-resolution earthquake catalog that has brought new insights to the evolution of the Tehuantepec earthquake. Here, we interpret these results together with relocated moment tensors in the context of regional plate tectonics. Moment tensor solutions indicate that the offshore rupture segment prior to crossing the Tehuantepec Ridge was mechanically complex, exhibiting a broad mix of faulting styles dominated by normal faulting. After crossing the Ridge only thrust mechanisms were observed. We interpret this as a rupture with two main stages (1) a normal, but significant complex breaking within the rupture before the Tehuantepec Ridge, then (2) a jump onto the megathrust interface. The earthquake stopped at what appears to be a break between the remaining sliver of the Caribbean plate and the North American plate. This suggests that part of the Tehuantepec gap did break in the rupture. To our knowledge, this represents the first documented case of a large normal-faulting earthquake transitioning directly from an outer-rise fault onto a megathrust interface.

Session: Linking Subduction Zone Processes and Cascading Hazards in Alaska, Cascadia, Chile and Beyond - II

Type: Oral

Date: 4/16/2026

Presentation Time: 03:15 PM (local time)

Presenting Author: Allen Husker

Student Presenter: No

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