Slow Slip Events in Mexico: A Historical Perspective

Víctor M. Cruz-Atienza , Sara Franco, Vladimir Kostoglodov, Josué Tago, Ekaterina Kazachkina, Jorge Real, Carlos Villafuerte, Raymundo Plata-Martinez

This paper introduces a historical catalogue of slow slip events (SSE) for the Mexican subduction zone. The catalogue incorporates all 25 SSEs recorded since they were discovered in 1997. The inversion of GPS data for ten SSEs in Guerrero and five in Oaxaca reveals a clear slow slip segmentation along the Middle America Trench, with slip maxima between 30 and 40 km depth in both regions. SSEs in Guerrero are significantly larger, with M_w=7.14±0.18 and a duration of 10.3±6.5 months, whereas in Oaxaca, M_w=6.84±0.16 with a duration of 7.0±4.3 months. Such discrepancy results from the subhorizontal geometry of the Cocos Plate in Guerrero, which favors a more extensive SSE habitat. The extent and along-strike segmentation of SSEs appear to be structurally controlled by the subduction of the Orozco and O'Gorman fracture zones. For the inversions, we used consistent GPS data processing that preserves the North American reference frame and the actual SSEs crustal rebounds. All data were curated to minimize seasonal noise, and interpreted throughout the ELADIN inversion method. Five of the six most recent M7+ earthquakes in the region were preceded and most likely triggered by an SSE. This earthquake cluster began after a 17-year period of quiescence, during which large SSEs occurred. While the SSEs appear to be necessary for initiating large ruptures, this is not enough until sufficient energy has accumulated in the seismogenic zone. The Mexican seismic record since 1800 suggests that every ~15 years the subduction zone reaches a critical state in which SSEs become large earthquake triggers.