Tomographic imaging of P- and S-wave velocity structure beneath Costa Rica

45287 P-wave and 26813 S-wave arrival times from the data base of the Costa Rica network have been tomographically inverted to image the structure ben eath Costa Rica. A regularized recursive least squares inverse method was u sed to produce the high resolution and minimum variance model parameter est imates. The first arrival times are calculated using a finite difference te chnique, which allows for flexible parameterization of the velocity model a nd easy inclusion of topography and source-receiver geometry. The P wave ve locity structure and hypocenters are determined simultaneously, while the S wave velocity structure is determined using the relocated seismicity and a n initial model derived from the P wave model assuming an average P to S wa ve velocity ratio of 1.78. The most prominent features in the inverted mode l are a low velocity structure under the volcanic chain in the center of th e country, which is related to the hot material connected with the active v olcanoes; and a high velocity zone in the mantle, which is related to the C ocos plate subducted under Costa Rica.