Seafloor geodesy unveils seismogenesis of large subduction earthquakes in Mexico

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 M_w7.0 (moment magnitude of 7.0) Acapulco, Mexico, earthquake in 2021. We exploit unprecedented ocean-bottom observations using ultralong-period "tilt mechanical amplifiers," along with hydrostatic pressure, global navigation satellite system, and satellite interferometric synthetic aperture radar data. The joint inversion of 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 M_w7.3 long-term SSE induced by the earthquake. Episodic near-trench oceanic-crust deformations (i.e., tilt transients) associated with shallow and deep synchronous decoupling of the plate interface reveal the occurrence of "slab-pull surges" before three regional earthquakes of magnitude 7 or greater, including the Acapulco event, suggesting that they may serve as rupture precursors observable in subduction zones.