Preliminary crustal structure of the coast of Guerrero, Mexico, using the minimum apparent velocity of refracted waves

Abstract

The seismic velocity structure beneath the coast of Guerrero, Mexico was determined using the minimum apparent velocities of refracted waves. The data used in the analysis is a selection of local earthquakes recorded by the Guerrero Seismic Network installed at the end of 1987 to monitor the seismicity of this seismic gap. The earthquakes were selected on the basis of the quality of their hypocentral location and to insure a homogeneous and complete sampling of the velocity structure of the study area. The results show that the crust in this subduction zone is composed of four layers with the following velocities and thicknesses: Vt=5.8, V2=6.5, V3=7.1 and V4=7.4 km/s; h1=10, h2=8.4 and h3=5.0 krn. No raypaths refracted from the Moho discontinuity were observed, although we included events far from the center of the network. The absence of a mantle refraction in this area may be interpreted as evidence that the lower crust of the overriding continental plate lies directly on top of the upper crust of the subducting Cocos plate without any intervening mantle layer. Detailed mapping of the megathrust seismic zone indicates that the approximate depth of the deepest crustal layer of the upper plate is similar to that of the interplate seismogenic contact.