Slow slip events and strain accumulation in the Guerrero gap, Mexico

Global positioning system (GPS) time series in Guerrero (Mexico) reveal the existence of large slow slip events (SSEs) at the boundary between the Cocos and North American plates. In this study, we examined the last three SSEs that occurred in 2001/2002, 2006 and 2009/2010, and their impact on the strain accumulation along the Guerrero subduction margin. GPS displacements were inverted to retrieve the slip distribution during each SSE and the inter-SSE coupling of the subduction interface. The three analyzed SSEs have equivalent moment magnitudes of between 7.50 and 7.65, their lateral extents are variable, and they all show significant slip in the Guerrero seismic gap. During the inter-SSE epochs, the interplate coupling is high in the area where slow slip subsequently occurs. In the Guerrero gap, the shallow portion of the plate interface from the trench to the coast is weakly coupled. The average slip deficit accumulated in the Guerrero gap over a period of 12 years, which corresponds to three cycles of SSE, is only 1/4 of the slip deficit accumulated on both sides of the gap. Moreover, the regions of large slip deficit coincide with the rupture areas of recent large earthquakes. We conclude that the SSEs in the Guerrero gap release a significant part of the strain accumulated during the inter-SSE period. If large subduction thrust earthquakes occur in the Guerrero gap, their recurrence time is probably increased compared to adjacent regions.