Studies of Seismic Sources, Ground Amplification, and Paleoliquefaction
Here we present a seismic source model for Puerto Rico, designed for use in probabilistic ground motion hazard analyses. The model consists of characterizations of known on- and offshore faults and their estimated geometries, the magnitudes of maximum earthquakes, one or more recurrence models for each fault, and activity rates for randomly occurring upper-crustal seismicity beneath the island. Slip rates for faults in the Mona and Anegada Passages were estimated by the allocation of GPS-based regional horizontal geodetic vectors onto appropriate groupings of faults. Rates for other sources were based on GPS vectors or empirical fits to Puerto Rico Seismic Network (PRSN) data.
Hazard curves for peak horizontal acceleration were computed by using the model for the four corners of the island. The hazard appears to be greatest in the western part of the island, which is closer to the more active sections of the two subduction zones and faults of the Mona Passage extensional regime. To the east the hazard is less because of presumed lower coupling between the North America and Puerto Rico–Virgin Islands microplate, and because of dispersion of relative motion at the Muertos subduction zone onto faults in the Anegada Passage and the Investigator faults south of the island. Recommendations for further work include further development of attenuation parameters, refinement of the local seismicity catalog, and further investigations into faults on and near the island.