Seismic studies of crustal structure in Nicaragua and Costa Rica



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This thesis verifies the crustal model of Southern Central America as inferred by Matumoto et al. (1977). The investigative techniques of this study differed from the earlier work in that (1) the P-MAV method was modified to delineate shallow structure, (2) the hithero untested S-MAV technique was applied to over 4000 regional earthquakes, (3) an iterative modeling scheme was applied to explosion data, (4) observed secondary phases were compared with theoretical travel times from a proposed crustal model. By use of the modified P-MAV technique, the proposed velocity values (Matumoto et al., 1977) for the two shallowest layers have been lowered from 5.1 km/sec and 6.2 km/sec to 3.8 km/sec and 5.6 km/sec respectively. It is inferred from this study that continental-type crust underlies northern Costa Rica. This suggests that Southern Central America is subdivided into different crustal blocks, hence different tectonic units.