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Amplitude and Q of 0S0 from the Sumatra Earthquake as Recorded on Superconducting Gravimeters and Seismometers

It has been known for some time that superconducting gravimeters (SGs) can provide excellent recordings of the seismic normal modes. Studies by Banka and Crossley (1999) and van Camp (1999) established the low noise level of SGs in the seismic normal mode band, especially at periods longer than 100 s. In an extensive study of all the currently operating SGs (about 18), Rosat et al. (2003) showed that the best SGs have lower noise than the New Low Noise Model (Peterson 1993) at periods longer than 1,000 s. Also, several studies have compared the performance of SGs and broadband seismometers at long periods and shown that the correction of meteorological influence on the SGs can be more effective than on seismometers (Freybourger et al. 1997; Hinderer et al. 2002). Zurn and Widmer-Schnidrig (2006) demonstrated the need to correct seismometers for pressure effects at long periods. In the frequency domain the sensitivity of SGs reaches 1 nanogal (10–11ms–2) or less, especially at periods longer than 100 s. Widmer-Schnidrig (2003) summarized the advantages of using SGs for long-period seismology, noting that in addition to sensitivity the SGs are calibrated to DC with an amplitude accuracy of better than 0.1%. Here we combine and compare, for the first time, seismic data from the Incorporated Research Institutions for Seismology (IRIS) Data Management System and data from SGs contributing to the Global Geodynamics Project (GGP) (Crossley et al. 1999).

The 26 December 2004 Sumatra earthquake is the largest event to be recorded both by the Global Seismographic Network (GSN) and SGs, with a magnitude larger than 9.0. It therefore provides a very good opportunity to test the calibration levels of our instruments (Davis et al. 2005; Park, Song, et al. 2005). Rosat et al. (2007).recently published a study that …