Generalized interpretation of the Nicoya Peninsula 3-D velocity models and associated hypocenters. Colour and values indicate V_P ; V_P/V_S shown in italics. The observed velocities agree well with P-wave velocities and crustal structure (dashed black lines) from wide-angle refraction data (Sallarès et al. 2001). The updip limit of interplate seismicity (red circles) may correspond to the mid crust/oceanic slab interface, identified by the transition from 5.8 to 6.4 km s⁻¹P-wave velocities. The continental Moho (Mc) appears between 32 and 40 km depth BSL, and the downdip limit of microseismicity clearly occurs updip of the continental Moho/oceanic slab intersection. The forearc mantle wedge may be 15–30 per cent hydrated based on decreased P-wave velocities and slightly elevated V_P/V_S. The oceanic Moho (Mo) is well resolved, and oceanic mantle P-wave velocities are normal with slightly elevated V_P/V_S.