Earthquake activity near Ascension Island, South Atlantic Ocean, as seen by a combined seismic/hydrophone array

Earthquake activity in the vicinity of Ascension Island is studied using data from a recently installed, very broadband seismographic station and a network of ocean hydrophones deployed around the island. The seismic station ASCN recorded 121 local earthquakes over a 188-day period. Distance from ASCN is computed for 41 of these events, most of which occurred at approximately 100 km--the distance to the Mid-Atlantic Ridge. A local magnitude scale is calibrated and applied to the same 41 events with magnitudes ranging from 0.4 to 4.2. Six earthquakes were located using data from the hydrophones and ASCN. Two of the earthquakes occur on the Ascension Fracture Zone 35 km northwest of the island and the other four near the ridgetransform intersection. The locations have errors less than 10 km and frequently less than 3 km. There is no direct evidence for seismicity connected with geothermal activity on Ascension Island during the observation period. Copyright (~) 1996 CNR. Published by Elsevier Science Ltd.