The velocity crustal structure and the Moho discontinuity have been determined from wide-angle and seismic refraction data across the Nicoya Peninsula and the neovolcanic zone of northern Costa Rica. The data analyzed here are from 8 terrestrial shots recorded at 120 closely spaced landstations. These onshore recordings complete earlier offshore investigations and results to perform a seismic velocity model along a transect of 250 km, from the outer rise to the back-arc basins. The oceanic Moho (M1) reaches 10 km depth W of the Middle American Trench (MAT), deepening progressively towards the isthmus to reach an angle of subduction of 35°down to 40 km depth. The obtained onshore velocity crustal structure is characterized by significant lateral changes in the surface velocity (from 2.0 km/s to 5.0 km/s) which are consistent with most outstanding geological units (ophiolitic outcrops, sedimentary basins, etc.), an upper crust of 4 km with velocities ranging 5.3-5.7 km/s, a mid crust with a mean thickness of 13 km and velocity variations of 6.2-6.5 km/s and a thick lower crust up to 20 km with velocities between 6.9 and 7.3 km/s. The Moho (M2) is attained at 38-40 km. We discuss herein the significance of this crustal structure as Caribbean crust over-thickened or essentially built by Galapagos mantle plume-derived material

18 pages, 6 figures, 2 tables