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For this study, Receiver Functions have been calculated using telesesimic events (mb > 5.4) recorded by the Pocosol Seismic Network, an NSF-funded array of three stations deployed by Rutgers University in Northern Costa Rica, and teleseismic events (mb > 5.9) recorded by station JTS from the Global Seismology Network and HDC from the Geoscope Project.

Our results show that the crustal thickness varies underneath the Costa Rican Isthmus. The Moho discontinuity is visible at depths of 36 km beneath stations of the Pocosol Network located in the back-arc region, 41 km underneath HDC located in the volcanic arc, and 37 km beneath JTS in the forearc region. Moho depths were estimated using a stacking algorithm which sums the amplitudes of receiver function of direct and multiply-converted phases. Our preliminary results suggest that there is a more complicated crustal structure underneath the forearc and the volcanic arc compared to the back arc region.

Fig. 2. Receiver functions with variance reduction of 85% for Pocosol stations A) Vp/Vs-thickness “bulls-eye” plots. B) Stacked receiver functions as a function of depth. C) Stacked receiver functions as a function of back-azimuth. D) Arrival time of first order and multiples of receiver functions as a function of ray parameter.

Fig. 3 Simplified 2D velocity-depth profile obtained from Sallares et al. (2001). See location of profile A-B in Figure 1. Triangles show the projection of the station location along the profile. Solid red line shows Moho according to Sallares et al. (2001) and yellow lines show the calculated Moho depths obtained here.

Reference

Sallarès, V. Dañobeitia, J. J., and Flueh, E., 2001. Lithosphere structure of the Costa Rica Isthmus: effects of subduction zone magmatism on an oceanic plateau. Journal of Geophysical Research, 106 (B1): 621-643.