Seismic Recording on Drifting Icebergs: Catching Seismic Waves, Tsunamis and Storms from Sumatra and Elsewhere

Abstract

Under the Incorporated Research Institutions for Seismology (IRIS) Program for Array Seismic Studies of the Continental Lithosphere (PASSCAL) project SOUTHBERG, we have operated for the past three years a number of seismic stations on giant Antarctic icebergs parked or drifting slowly along the margins of the Ross Sea. The purpose of this deployment was to investigate in situ the characteristics and origin of high-frequency tremors emanating from inside the icebergs, tremors that previously had been detected in the far field as hydroacoustic T phases recorded in French Polynesia (Talandier et al. 2002, 2006). Similar observations were made later in the Indian Ocean by Chapp et al. (2005). In this general context, the purpose of this paper is to report on the ancillary functioning of iceberg-sited seismometers as teleseismic observatories, and in particular their recording of the two Sumatra mega-earthquakes of 26 December 2004 and 28 March 2005. These data are available upon request from the authors. We are in the third and final year of the SOUTHBERG deployment. In November–December 2003, we installed four seismic stations on iceberg C16 (including an STS-2 broadband instrument at the central station C16A) and left one of them to winter over during 2004. Because all stations work on solar power, the station shut down on 28 May 2004 after the arrival of permanent winter darkness at that latitude, but it woke up and started recording uneventfully on 25 September 2004 around the austral spring equinox, thus providing a total of 141 days of seismic recording, which went beyond our expectations. Bolstered by this performance, we left four stations to winter over in 2005: one at C16A (hereafter referred to as C16 for short), one on iceberg B15A, one on iceberg B15K (a fragment of B15A that detached in 2004), and one on …