Seafloor structure near the epicenter of the great 25 March 1998 Antarctic Plate earthquake

Abstract

[1] The great Antarctic Plate earthquake (M 8.1) that took place on 25 March 1998 was one of the largest oceanic intraplate strike-slip events ever recorded, but the cause of the earthquake is still unclear. Detailed marine geophysical surveys were conducted near the epicenter of the earthquake, and the results of swath bathymetry and the magnetic and gravity anomalies are presented. The data revealed the detailed structure of a seamount just south of the epicenter of the main shock. Two possible structures, which may represent the faults of the Antarctic Plate earthquake during the first subevent, were inferred from the geophysical data collected during the cruise by taking the uncertainties in the location of the epicenter and the distribution of the aftershocks into account, and the foot of the north-side escarpment of the seamount may indicate the main fault of the first strike-slip subevent of the Antarctic Plate earthquake. The north-side escarpment of the seamount was most likely formed before the Antarctic Plate earthquake, indicating that the earthquake occurred along preexisting structures. The magnetic anomaly and structural trends near the seamount are different from those in adjacent areas, and the area near the seamount is likely a block that was captured during ridge reorganization. Moreover, the area near the seamount may be a crustal fragment that was formed during initial rifting between Antarctica and Australia.