Course: Seminar II (for second-year MSc students)

Detecting Sea Level Change Due to the 2004 Sumatra-Andaman Earthquake Using EOF Method

Yi Hsiang Li

Abstract

The magnitude MW=9.3 earthquake in Sumatra-Andaman on December 26, 2004, was the second largest earthquake in the past century, rupturing along a 1200-km long reverse fault delineated by aftershocks. In this study we use the sea level change as a proxy for the regional geoid change (because the mean sea surface conforms to the geoid), focusing on the co-seismic and post-seismic behavior. For the sea level, we use the radar altimetry data form several satellites (Topex/Poseidon, Jason-1, GFO, Envisat, ERS-2) available from AVISO, from 2003 through 2006 (four years), with gridded resolution of 0.3° and time interval of seven days. We select the region of 15°N ~ 10°S and 90°E ~ 115°E. We calculate the EOF (Empirical Orthogonal Function) to analyze the space-time variation of the sea level signalbefore and after the Sumatra-Andaman earthquake. Besides the strongest but climate-induced mode which is highly correlated with the ENSO index, we find that the second strongest mode signifiesthe geoid change caused by the earthquake. This mode also shows a post-seismic recovery of the geoid on a timescale of about two years. We compare this result with recent findings from the GRACE satellite dataof time-variable gravity, and confirm that both results of geoid change from pre-seismic to post-seismic are consistent.

Reference

Ryoko Ogawa, Kosuke Heki ,Slow postseismic recovery of geoid depression formed by the 2004 Sumatra-Andaman Earthquake by mantle water diffusion, Geophys. Res. Lett, VOL. 34, L06313, dori:10.1029/2007GL029340,2007

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J. L. Chen, C. R. Wilson, B. D. Tapley, and S. Grand, GRACE detects coseismic and postseismic deformation from the Sumatra-Andaman earthquake, Geophys. Res. Lett, VOL. 34, L13302, doi:10.1029/2007GL030356,2007

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Yutaka Hayashi et al. , Feasibility study on the potential of satellite altimetry for detecting seismic geoid changes due to the 2004 Sumatra-Andaman earthquake, Earth Planets Space,59,1149-1153,2007

(Abstract) (Full text)