LOADING AND GRAVITATIONAL EFFECTS OF THE 2004 INDIAN OCEAN TSUNAMI AT SYOWA STATION, ANTARCTICA

Abstract

The 2004 Indian Ocean tsunami reached Syowa Station, Antarctica, approximately 12.5 hr after the December Sumatra-Andaman earthquake. We have analyzed the tsunami signals recorded on ocean-bottom pressure gauges, broadband seismometers (STS-1), and a superconducting gravimeter (SG). We calculated the sea level variation, tilt, and gravity changes induced by the tsunami and compared these results to observations. From this comparison we confirmed the loading and gravity effects of the tsunamis on the STS-1 (horizontal components) and the SG records at Syowa Station. The magnitudes of these effects given as root mean square amplitudes are as follows: for the tilt effects obtained from 20-hr-long STS-1 records at frequencies in the range 0.3-0.6 mHz, 5 and 8 μGal (10-8 m/sec2) in the east-west and north-south directions, respectively; and for the gravity effect obtained from the SG records for the same time period of 20 hr at frequencies in the range 0.1-0.2 mHz, 0.2 μGal. By using detailed bathymetry around Syowa Station, the synthetic amplitudes similar to the observed were obtained, although the waveforms of synthetic and observation are not always consistent.