Focal mechanisms and seismic moments of large earthquakes in the Antarctic Peninsula-Drake Pasage region (abstract)

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Fault plane solutions and seismic moments of four largest shallow events which occurred in the Antarctic Peninsula-Drake Passage region were redetermined by the moment tensor inversion method (FITCH et al. : J. Geophys. Res., 85,3817,1980) for body waves on WWSSN long-period records. The June 15,1970,event (Ms 7.0) is a large transform fault event along the North Scotia Ridge between the South America and the Scotia plates with a moment of 3.7×(10)^<26>dyn・cm. The February 8,1971,event (Ms 7.0) is a large normal faulting event with a moment of 2.4×(10)^<26>dyn・cm in the South Shetland Islands, north off the Antarctic Peninsula. The December 29,1975,event (Ms 6.5) is a vertical dip slip fault event with a moment of 0.7×(10)^<26>dyn・cm, which was located in the north of the Drake Passage and was probably associated with the spreading between the Antarctic and the Scotia plates (BARKER : Antarctic Geology and Geophysics, ed. by ADIE, 17,1972). The mid-plate event (Ms 6.2) of February 5,1977,is a reverse faulting with a moment of 0.5×(10)^<26>dyn・cm, which is one of the largest mid-plate events in the world. The direction of the maximum compression of the event is 100°-110° clockwise from the north and is coincident with the spreading directions at the Pacific-Antarctic Ridge and the Atlantic-Indian Rise.
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