Seafloor Geodesy Unveils Seismogenesis of Large Subduction Earthquakes in México

Seafloor geodesy may lead to deep understanding of subduction systems and seismogenesis. Based on measurements of near-trench deformations of the oceanic and overriding plates, in this investigation we elucidate the tectonic and mechanical processes leading to the Mw7.0 Acapulco, Mexico, earthquake in 2021 at the heart of the Guerrero seismic gap. We exploit unprecedented ocean-bottom observations using new ultra-long-period ‘tilt mechanical amplifiers’, along with hydrostatic pressure, GNSS, and satellite InSAR data. The joint inversion of all these geodetic data, template matching seismicity and repeating earthquakes, revealed the first two shallow slow slip events (SSEs) observed in Mexico. The first one migrated from the trench to the earthquake hypocenter before rupture, and the second one occurred following an Mw7.7 long-term deeper SSE induced by the earthquake. Near-trench oceanic-crust episodic deformations (i.e., tilt transients) associated with shallow and deep synchronous decoupling of the plate interface reveal the occurrence of ‘slab-pull surges’ across the subduction channel prior to three M7+ regional earthquakes including the Acapulco event.