Probabilistic seismic hazard and the adequacy of existing building codes in Puerto Rico

ABSTRACT

Puerto Rico has a long history of damaging eartquakes with the events of 1787, 1867, and 1918 being the strongest since the first earthquake was described in the early 1500s. However, the origin of local earthquakes has been the subject of controversy. Some of this controversy has been reduced with the recent discovery of active faults which allows for a better understanding of regional seismotectonics. This paper attempts to incorporate this new information in reassessing the seismic hazard of Puerto Rico. Our methodology is similar to procedures defined in the U.S. by the Lawrence Livermore National Laboratory (LLNL) and the Electric Power Research Institute (EPRI) for assessing the seismic hazard of the nuclear power plants. Random values of the parameters used to define seismic recurrence are introduced by means of a Monte Carlo simulation process following a triangular probability distribution about the best estimate value for each parameter. Results of the analysis indicate that the seismic hazard of Puerto Rico is fairly uniform, similar to the assumptions of locally applied building codes, although there is some variation. The San Juan area has the least seismic hazard and the southern coast has the greatest hazard, somewhat in contradiction to the historical seismicity. Although the Muerta Trough has fewer large earthquakes than the Puerto Rico Trench, it is much closer to land and the potential for serious damage on the southern cost is greater. The UBC seismic design criteria appear to be reasonably conservative for Puerto Rico, although it is cautioned that this study does not account for soil amplification which could be an important local consideration (AU)