THERMAL MODELS, COUPLING AND METAMORPHISM FOR THE MEXICAN SUBDUCTION ZONE BENEATH GUERRERO

It has been proposed that the seismogenic coupled, and transition, partially coupled zones are controlled, among other factors, by the temperature. The coupling zone inferred from the GPS data for the steady interseismic period and also for the last slow aseismic slip event that occurred in Guerrero in 2001-2002, extends up to 180 Km - 220 Km from trench. Previous thermal models for the subduction zone in Guerrero do not take into account this extremely wide coupled zone. To investigate whether thermal models can explain this wide coupled area beneath Guerrero we developed the steady-state thermal models for the 180 Km and 220 Km coupled zones. The updip limit of the seismogenic zone is taken between 100 ºC and 150 ºC, while the downdip limit is thought to be at 450 ºC as the transition from stick-slip to stable sliding. Between 350ºC and 450 ºC a partial coupling might exist, and the silent earthquakes may occur. We introduced in the models a small quantity of frictional heating in order to fit the intersection between the 450 ºC isotherm and the subducting plate surface at 180 Km - 205 Km from the trench. The models show a decrease in the heat flow from the trench towards the continent, which is typical for the Mexican subduction zone. The calculated geotherms in the slab and the phase diagram for MORB are used to estimate the metamorphic sequences within the oceanic subducting crust. A correlation exists between the metamorphic sequences along the subducting plate and the extension of the coupled patches assessed in the model of the surface deformation produced by the last silent earthquake and also during the interseismic period. Our thermal models indicate that the seismogenic zone the subduction zone beneath Guerrero limited with between 100 ºC - 150 ºC and 350 ºC is in good agreement with the seismic rupture width inferred from the aftershock distribution and seismic models of rupture.