Geodetic measurements from a network of permanent GPS stations along the Pacific coast of Mexico reveal a large “silent earthquake” along the segment of the Cocos‐North American plate interface identified as the Guerrero seismic gap. The event began in October of 2001 and lasted for 6–7 months. Average slip of ∼10 cm produced measurable displacements over an area of ∼550 × 250 km2. The equivalent moment magnitude of the event was Mw ∼ 7.5. Recognition of this and previous slow event here indicate that the seismogenic portion of the plate interface is not loading steadily, as hitherto believed, but is rather partitioning the stress buildup with episodic, as opposed to steady‐state or periodic, slip downdip of the seismogenic zone. This process increases the stress at the base of the seismogenic zone, bringing it closer to failure. These results call for a reassessment of the seismic potential of Guerrero and other seismic gaps in 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.

Studies of low‐frequency earthquakes (LFEs) have focused on detecting events within previously identified tectonic tremor. However, the principal LFE detection tools of matched‐filter searches are intrinsically incapable of detecting events that have not already been characterized previously as a template event. In this study, we therefore focus on generating the largest number possible of LFE templates by uniformly applying a recently developed LFE template detection method to a 2.5 yearlong data set in Guerrero, Mexico. Using each of the detected templates in a matched‐filter search, we then form event families that each represents a single source. We finally develop simple, empirical statistics to select the event families that represent LFEs. Our resulting catalog contains 1120 unique LFE sources and a total of 1,849,486 detected LFEs over the 2.5 yearlong data set. The locations of the LFE sources are then divided into subcatalogs based on their distance from the subduction trench. Considering each LFE as a small unit of slip along the subduction interface, we observe discrete episodes of LFE activity in the region associated with large slow‐slip events; this is in direct contrast to the near‐continuous activity observed 35 km farther downdip within the previously identified LFE/tremor sweet spot.

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Abstract. The Guerrero region of southern Mexico has accumulated more than 5 m of relative plate motion since the last major earthquake. In early 1998, a continuous GPS site in Guerrero recorded a transient displacement. Modeling indicates that anomalous fault slip propagated from east to west along-strike of the subduction megathrust. Campaign GPS and leveling data corroborate the model. The moment release was equivalent to an M•o_>6.5 earthquake. No M>5 earthquakes accompanied the event, indicating the frictional regime is velocity-strengthening at the location of slip.