Earthquake Activity near Ascension Island as seen by a Combined Seismic/Hydrophone Array.
Abstract
Data from a recently installed Global Seismographic Network station on Ascension Island in the central Atlantic Ocean (IRIS/IDA ASCN) are used in conjunction with data from a network of ocean hydrophones (MThS network) deployed around the island to detect and locate background seismicity associated with the mid-Atlantic Ridge and nearby transform faults. Locations calculated from the combined data set have errors less than 10 km, and frequently less than 3 km. A local magnitude scale based on S-wave amplitudes at the seismic station is devised. We estimate a detection threshold of about magnitude 1.7 for earthquakes occurring on the nearby part of the ridge, 120 km away; this is almost three orders of magnitude smaller than the smallest events from this region in the PDE or REB catalogs. No natural seismicity on Ascension Island itself was seen during a 200-day observation period. The seismic station regularly records large T-phases from moderate-sized events around the Atlantic. T- phases are more pronounced at IRIS/IDA station SHEL on St. Helena Island, 1290 km southeast of Ascension Island, probably due to its steeper topography. Taken together, the seismic stations ASCN, SHEL, and the MILS network represent a unique facility to monitor seismic events in the south Atlantic. (MM)
Document Details
- Document Type
- Technical Report
- Publication Date
- Feb 01, 1996
- Accession Number
- ADA304874
Entities
People
- Holly K. Given
- Jeff A. Hanson
- Jonathan Berger
Organizations
- Scripps Institution of Oceanography