Seismic Activity Associated with Surface Environmental Changes of the Earth System, around Syowa Station, East Antarctica

The Japanese Antarctic Station, Syowa (69° S, 39° E; SYO), is located on Lützow-Holm Bay of western Enderby Land, East Antarctica. Seismic observations at SYO started in 1959, and the arrivaltimes of the major phases for teleseismic events have been reported from the National Institute of Polar Research every year since 1968. Here, we summarize records from local earthquakes around SYO in the last three decades. In particular, the fifteen years since 1987 divided into three periods are examined in detail, with respect to the location of epicenters and estimation of magnitudes. A three-station seismic array was deployed around SYO in 1987–1989. By using these data, epicenters of local earthquakes were determined for the first time. Many different types of earthquakes, such as a mainshock-aftershock sequence, twin earthquake, and earthquake swarms were detected and clearly identified. The seismic activity during this period was higher than that of the following decade. Earthquake location was concentrated along the coast and central Lützow-Holm Bay.

In the next period between 1990–1996, nine local earthquakes were classified in many different types. The seismicity during this period was very low and magnitudes ranged from 0.1 to 1.4. Hypocenters of four earthquakes out of nine were localized in Lützow-Holm Bay and its northeastern coastal area by a single station method using SYO data. One local event was detected in 1997, two events in 1998 and one event in 2001 and 2003, respectively. The low seismic activity has continued to date (December 2003). The observed offshore location and low level off seismic activity is consistent with a glaciogenic component to the stress field causing the earthquakes.