New insights into geomorphological and tectonic processes in the Gulf of Tehuantepec and constraints on tsunami generation

Abstract

Earthquakes can cause tsunamis by rapidly deforming the seafloor or triggering submarine slope failures. The intraplate earthquake in the Gulf of Tehuantepec on September 8, 2017 generated a tsunami that did not match the predicted tsunami run-up heights and distributions, indicating a possible additional slope failure. An oceanographic expedition, TEHUANTEPEC19, was carried out between May and June 2019, onboard the El Puma vessel, during which bathymetric, magnetic, and high-resolution seismic data were gathered and evaluated together with pre-existing seismic data. The results document a wide range of erosion-deposition processes in the region including past submarine landslides. However, the mapped landslide deposits are already heavily overprinted by gully formation and sedimentation, ruling out that submarine slumping influenced the recent tsunami after the 2017 Tehuantepec earthquake. Other geological processes, such as subsidence and extension of the forearc, large numbers of faults, and the subduction of the Tehuantepec Ridge, suggest that the Tehuantepec shelf is dominated by subduction erosion. This process may have deformed the continental shelf more complexly than assumed for the earthquake-derived tsunami model, explaining the mismatch between modeled and observed tsunamis. Our findings indicate that slope failure-induced tsunamis can play a role on the coasts of Central America, but this was not the case for the 2017 Tehuantepec earthquake.