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OBS Recovery off Puerto Rico

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The temporary array of 15 land and ocean bottom seismometers (OBSs), which was deployed in early May in and around western Puerto Rico, was successfully recovered during June 13th-16th. All stations appear to have recorded data. The network was installed to record local and regional earthquakes as part of a series of studies planned to better assess the hazard to Puerto Rico and the Virgin Islands from earthquakes, submarine slides, and tsunamis. The data collected by the temporary array were augmented by data collected by the permanent seismic stations of the Puerto Rico Seismic Network. The combined data sets will be used to locate earthquakes more accurately than is presently possible, because the accuracy of an earthquake location depends on the distance from the earthquake to the seismometers and on the geographical distribution of the seismometers. Many of the marine and land seismometers were placed at intervals of 15-25 km along two perpendicular arrays. One array was along a 150-km-long north-south line crossing the Puerto Rico platform along the western side of the island, and the other was along a 250-km-long east-west line along the south part of Puerto Rico with continuation to Mona Island. The data from these arrays will be used to construct seismic-velocity maps of the Earth's crust under the arrays. Seismic velocity is a good proxy for the types of rocks at depth. USGS scientists also hope to learn about the attenuation of seismic energy from the earthquake at particular seismic stations.

This study is being carried out jointly by the USGS Coastal and Marine Program in Woods Hole and by the Puerto Rico Seismic Network at the University of Puerto Rico. The USGS CMGP, Puerto Rico Department of Natural and Environmental Resources (DNER), Sea Grant Office at the University of Puerto Rico, Mayaguez, and the President's Office of the University of Puerto Rico funded the study. Uri ten Brink, Greg Miller, Erich Roth, Jeff Nealon, (WHFC), Russell Sell (EHP, Menlo Park) Robert Iuliucci (contractor), Kurt Grove (Puerto Rico Sea Grant Office), Ramon Alonso (Puerto Rico DNER), David Martinez (Dept. of Geology, University of Puerto Rico), and Rafael Abreu and Samuel Vega (Puerto Rico Network) recovered the OBSs using the University of Puerto Rico's R/V Chapman. The three temporarily installed land seismometers were picked up by Russell Sell and Erich Roth at the end of the cruise. The marine component represents the largest number of OBSs to date in a single deployment, the first time that all newly designed USGS OBSs with external geophones were used, and the first time that USGS OBSs were deployed in a regional network to record earthquakes. The modified OBSs represent the culmination of several years of hard work by Greg Miller and Ray Davis to upgrade the instruments in order to improve their new mission of recording earthquakes better.

After returning to port, the R/V Chapman was visited by several Press representatives who were briefed by Christa von Hillebrandt-Andrade, Director of the Puerto Rico Seismic Network, and Uri ten Brink about the goals of the cooperative experiment and the instruments. The generous help of Joe Fletcher and Russell Sell, the Puerto Rico Port Authority of Mayaguez, the President's Office of the University of Puerto Rico, and the staff of the Puerto Rico Seismic Network in various aspects of the experiment were central to its success.

Related Sound Waves Stories
Puerto Rico OBS Study
June, 2000

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