Long-lived tsunami edge-waves within the Tehuantepec Gulf triggered by the Mw8.2 Tehuantepec earthquake

The Mw8.2Tehunatepec earthquake produced a relatively small tsunami that was recorded at several tide gauge stations nearby the epicenter. The regional bathymetry in the Gulf of Tehuntepec is characterized by a large continental shelf with up to 100km of length followed by a steep slope. This particular case of contiental shelf morphology creates the suitable conditions to trap tsunami waves within the continental shelf. Using numerical modeling tailored to local observations we show that long-lived edge waves could remain in the region, as perturbations, for more than 48hrs. We identify the edge wave by studying the tide-gauge tsunami codas. The tide-gauge stations close to the end of the continental shelf (Salina Cruz) recorded smaller tsunami coda than the station surrounded by an extended shelf on both sides (Puerto Chiapas). Interestingly, this particular station, the largest wave was not the first one but rather a later arrival that came 5 hours after the main incident wave. This strongly suggests that trapped-edge-waves have a constructive interference that focus the wave energy towards the region along the coast where this tide gauge is located. Tsunami simulations based on a source model inverted from regional geophysical observations show a good agreement with the observations recorded tide gauges. Additionally, our simulations reveal an important effect (edge waves) that usually is not considered for tsunami hazard maps and early warning. In the particular case of Mw8.2 Tehuantepec earthquake the magnitude and type of fault mechanism did not generate a large tsunami. However, a potential tsunamigenic event near the trench, and eventually within the Tehuantepec Gap, can trigger a large tsunami.Our study shows that the resonant effects due to trapped-edge-waves represents a potential threat that should be considered for future hazard maps and tsunami warning systems.