A Simplified Method to Invert Slow Slip Events: Examples for the 2002, 2006 and 2014 events in Guerrero, Mexico

Abstract

An efficient method to obtain a simple model of the slip distribution on a fault plane was developed from estimates of static offsets from continuous GPS measurements. Transfer functions were computed for the displacement due to a unit force on a fault plane (with a predetermined geometry, subdivided in a dense grid of subfaults) for all combinations of stations and subfaults, considering a layered media. The forward problem is built as a linear combination of elliptical slip-patches over the fault plane and the transfer functions between each patch and each station. To test the method, the 2002, 2006 and 2014 slow slip events (SSE) were modeled in Guerrero, Mexico, assuming that slip occurred along the subduction interface between the Cocos and North America plates. This subduction fault was modeled as two adjacent planes, both striking 289° for 600 km approximately parallel to the Middle America trench and with a width of 120 km (240 km total width). The shallower plane starts at the trench and dips 14° and the deeper plane is sub-horizontal (2° dip). The merged fault plane is segmented in 120x48, 5x5 km2 subfaults. A pre-calculated set of transfer functions is kept for future slow slip events, so that these only need to be computed for new GPS stations. A strong agreement between observations and synthetic data was found for all analyzed events, and the results are consistent with those reported by previous studies.