Proceedings of the 12th International INQUA meeting on paleoseismology, active tectonic and archaeoseismology

I N T R O D U C T I O N Large earthquakes with magnitudes exceeding 8 Mw, and megaearthquakes surpassing 9 Mw, frequently occur along subduction zones, exemplified by events in Chile (1960), Sumatra (2004), and Japan (2011). The Guerrero seismic gap (GSG), a roughly 200 km-long segment of the Mexican subduction zone (MSZ), is notably characterized by low seismic activity (Fig. 1). It is speculated that a potential rupture across the entire gap could yield an earthquake of magnitude Mw=8.4 (Suárez et al, 1990). Such an event would significantly impact the Mexico City metropolitan area, home to over 22 million people. Moreover, coastal communities like Acapulco could face substantial damage from a resultant catastrophic tsunami. Recent hypotheses propose that the rheology within the GSG promotes slow slip over fast slip (Husker et al., 2018). However, this hypothesis lacks comprehensive evaluation of historically and late Holocene tsunamigenic earthquakes. Our geological findings spanning approximately 2000 years reveal a history of significant tsunamis triggered by local earthquakes within the GSG. Modelling supports the potential occurrence of a large tsunamigenic earthquake with a magnitude exceeding 8 Mw, demonstrating a prolonged and variable occurrence (Ramirez-Herrera et al., 2024). These findings suggest a heightened likelihood for similar events in the future. Fig. 1: Tectonic and seismic setting of the Mexican Subduction zone. a – Large earthquakes (M>6.5) of the last century and rupture areas along the Mexican subduction zone. b - Guerrero segment, image shows topographic roughness on the subducting Cocos plate, c - Location of studied sites A1 and A2 along the Guerrero coast. (Modified from Ramirez-Herrera et al., 2024).