The silent earthquake of 2002 in the Guerrero seismic gap, Mexico (Mw=7.6): Inversion of slip on the plate interface and some implications

We invert GPS position data to map the slip on the plate interface during an aseismic, slow-slip event, which occurred in 2002 in the Guerrero seismic gap of the Mexican subduction zone, lasted for ~4 months, and was detected by 7 continuous GPS receivers located over an area of ~550x250 km2. Our best model, under physically reasonable constraints, shows that the slow slip occurred on the transition zone at a distance range of 100 to 170 km from the trench. The average slip was about 22.5 cm (Mo~2.97 x1027 dyne-cm, Mw=7.6). This model implies an increased shear stress at the bottom of the locked, seismogenic part of the interface which lies updip from the transition zone, and, hence, an enhanced seismic hazard. The results from other similar subduction zones also favor this model. However, we cannot rule out an alternative model that requires slow slip to invade the seismogenic zone as well. A definitive answer to this critical issue would require more GPS stations and long-term monitoring.