Seismotectonics and lithospheric structure of Costa Rica

Abstract: The interaction of different tectonic features on a short-distance scale of 100's of km produces the complexity of the Costa Rica region. The intraplate Caribbean earthquake activity of shallow-depth nature is mainly concentrated along an E-W axis in the central part of the country. All types of faults are presented in this region, although a strike-slip fault system, with NB-SW direction is proposed. Intraplate Caribbean esrthquakes in northwestem Panama are shallow and dominated by thrust fault motion. The seismicity along the Pacific coast is mainly associated with the subduction of the Cocos under theCaribbean plate, with predominant thrust fault mechanisms. The interaction of the Cocos and Nazca plates in southeastem Costa Rica, along the Panama fracture fault system produces events with strike-slip mechanism.A proposed 1D P-velocity model for the region is presented. Relocation of earthquakes of this area made through this ID-velocity model provides a reliable geometry of the Wadati-Benioff zone, with a slab dipping at 45° to a maximum depth of approximately 250 km.Station corrections and P- and S-velocity distribution correlate well with the major upper crust geological features of the area. The P- and S-velocity distribution for depth below 30 km shows a lateral velocity variation, which is associated with the subductionslab.