Local earthquake tomography in Central Pacific margin of Costa Rica 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...