Seismic Study of the Agua de Pau Geothermal Prospect, Sao Miguel, Azores

Abstract

A seismicity study of the Agua de Pau volcano and adjacent areas on Sao Miguel Island, Azores, was carried out jointly by the U.S. Geological Survey (USGS) and the Laboratorio de Geociencias e Tecologia (LGT) of the Regional Government of the Azores (RGA) from Jun 19 to October 10, 1983. A 16 station array was operated over the 200 km2 central portion of Sao Miguel utilizing 8 permanent Instituto Ncional de Meterologia e Geofiscica (INMG) stations and 8 USGS portable stations. Forty four local events with well constrained solutions and 15 regional events were located. In addition, hundred of unlocatable seismic events were recorded. the most interesting seismic activity occurred in a swarm on September 6 and 7, 1983 when over 200 events were recorded in a 16 hour period. The seismic activity around Agua de Pau was centered don the east and northeast slopes of the volcano. Low Vp/Vs ratios for the local events an low P velocity in the upper crust inferred from a study of regional earthquake residuals suggest a boiling hydrothermal system beneath the Agua de Pau volcano, consistent with a variety of other data.