Slow slip events in Mexico: A historical perspective

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 in 2012 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 regionally accumulated in the subduction 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 precursors. This paper presents a historical catalogue of slow slip events (SSE) for the Mexican subduction zone. The catalogue incorporates all 25 SSEs recorded since 1997, when these transient slip events were first discovered in Mexico and the Cascadia subduction zone. The catalogue was built using consistent GPS data treatment and modelling tools. This ensured the reliability of the resulting extend of the events in the states of Guerrero and Oaxaca for interpretations over the last 28 years, as shown by the blue shades in the figure. Following a prolonged period of seismic quiescence (i.e. between 1995 and 2012) spanning 17 years, six earthquakes with magnitudes greater than seven occurred in these states. Notably, all of these seismic events were preceded by an SSE near the hypocenter. It has been demonstrated that five of them were in fact triggered by the preceding SSEs. This indicates that seismic hazard may rise during the occurrence of aseismic slip transients in the plate interface. However, there were also large SSEs during the seismic quiescence period, suggesting that SSEs are a necessary but insufficient process for initiating large-scale seismic events. The Mexican record since 1800 indicates that major seismic events tend to occur in clusters, with an approximate duration of 15 years following a period of quiescence. This suggests that the subduction zone periodically reaches a critical state during which SSEs become large earthquakes precursors. • Catalogue of slow slip events (SSEs) in Mexico since their discovery. • SSEs in Guerrero are larger and longer than those in Oaxaca. • The spatial distribution of SSEs is determined by the geometry of the plate interface and fracture zones in the incoming Cocos plate. • Slow slip events become precursors to large earthquakes every ~15 years.