Inhalt: | The Central Pacific area of Costa Rica is a convergent erosional margin, characterized by a high seismicity rate, coincident with the subduction of rough-relief ocean floor. It has generated earthquakes with magnitude up to seven in the past along the subduction megathrust and the inner-forearc faulting. This study uses the records from a temporal seismological network, consisting of on- and offshore stations, installed for a period of six months in this segment of the Middle American margin. The aim was to obtain a model of the 3-D velocity structure of the margin and to characterize the seismicity of the shallow part (< 70 km depth) of the subduction zone, with the focus on the seismogenic zone. A subset of well locatable events was selected to calculate a minimum 1-D model for the P-wave velocity. This model served as initial reference model for the subsequent 3-D inversion in a Local Earthquake Tomography, performed by inverting P- and S-wave traveltimes from 595 selected earthquakes. Several tools for resolution assessment were applied. Additionally, first-motion, double-couple focal mechanisms were determined for earthquakes originated at the plate interface, the subducting slab and the overriding plate. The results reflect the complexity associated to subduction of ocean-floor morphology and the transition from normal to thickened subducting oceanic crust... |
