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 usi ng data from a recently installed, very broadband seismographic statio n and a network of ocean hydrophones deployed around the island. The s eismic station ASCN recorded 121 local earthquakes over a 188-day peri od. Distance from ASCN is computed for 41 of these events, most of whi ch occurred at approximately 100 km-the distance to the Mid-Atlantic R idge. 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 earthquak es occur on the Ascension Fracture Zone 35 km northwest of the island and the other four near the ridge-transform intersection. The location s have errors less than 10 km and frequently less than 3 km. There is no direct evidence for seismicity connected with geothermal activity o n Ascension Island during the observation period. Copyright (C) 1996 C NR. Published by Elsevier Science Ltd.