The Current State of Seismic Monitoring in Puerto Rico

Abstract

The U.S. Commonwealth of Puerto Rico has a population of 3.8 million (2000 Census), a higher population density than any U.S. state. The island, approximately 160 km east to west by 50 km north to south, is bounded by offshore active faults on all sides. Numerous local and regional events in the recorded history with M > 7.0, some of which have generated tsunamis, have caused extensive damage to local infrastructure, though the last significant ground motions were felt onshore in 1918. The U.S. Geological Survey hazard maps (Mueller et al. 2003) indicate that the seismic hazard is similar to the Basin and Range province in the Western United States, and the island is assigned Seismic Zone 3 in the current standard building code in Puerto Rico, the 1997 UBC. The significant hazard, combined with the large population and untested infrastructure, results in a potentially devastating combination for Puerto Rico. Efficient emergency response in the event of a large earthquake will be crucial to minimizing the resultant loss of human life and disruption of lifeline systems. The first step in providing an appropriate response to such a disaster is a timely knowledge of the magnitude, location, and expected ground shaking and damage patterns from a large earthquake. This requires a modern and dense seismic network, capable of not only recording the earthquake ground motion without saturation but also doing so in real time and then providing data for near-immediate analysis that can be made available to emergency services and the community at large. The seismicity of the island, as well as the northeastern Caribbean region in general (including the U.S. and British Virgin Islands), is monitored jointly by the Puerto Rico Seismic Network (PRSN) and the Puerto Rico Strong Motion Program (PRSMP), both operating within the University of Puerto Rico …