Intermediate-focus earthquakes under South Shetland Islands, Antarctica

Abstract

This study is based on data from five field surveys (1992–1996) of seismic monitoring on Deception Island (South Shetland Islands, Antarctica). In the 1994–95 and 1995–96 surveys earthquakes were recorded by a seismic array. In previous surveys data were collected by a high-dynamic range, short-period station. The analysis of the events shows evidence of intermediate-focus seismicity [50 < H< 100 km] related to the underplating zone of the South Shetland plate. Because of poor station coverage we had to use unconventional techniques to locate the events, such as zero lag cross-correlation method that provide information about apparent velocity and back-azimuth, ray-tracing procedure and particle motion patterns. These criteria allowed us to identify 15 earthquakes that could be considered as intermediate-focus events, for which some focal parameters were estimated. We conclude that the subduction zone between the Drake plate and South Shetland microplate has a moderate level of intermediate-depth microseismicity.