Seismicity variations associated with aseismic transients in Guerrero, Mexico, 1995-2006

Primarily aseismic deformation transients in subduction zones, sometimes associated with tremors and low-frequency earthquakes, are a newly recognized mode of deformation. Stressing in the up-dip seismogenic zone is increased episodically due to down-dip transient slips, and each event may make it more prone to failure in a large thrust earthquake. It is important for seismic hazard assessment to search and identify patterns of seismicity variation associated with transients. The Guerrero, Mexico, region is chosen for this study because of long-term continuous geodetic observations and abundant seismicity in the shallow subduction zone. We search the GCMT and NEIC catalogs for earthquakes with depths less than 100 km between 1995 and 2006 within the area coveting the region affected by major transients since 1996. A completeness magnitude of M-c=4.5 is determined for the NEIC catalog used in this study, based on the maximum likelihood method. Three large transients in 1998, 2001-2002 and 2006 are all temporally correlated with high seismic rates in the studied area. In particular, transients are either preceded by a cluster of extensional earthquakes relatively far inland from the trench, or followed by shallow thrust earthquakes close to the trench. In some cases, such as the 2001-2002 transient, both types of activity are found bordering the transient. The assembled evidence suggests that transients may serve as a mechanism of stress communication between distant seismicity clusters in shallow subduction zones. (C) 2007 Elsevier B.V. All rights reserved.