The Radiated Energy of the 2004 Sumatra-Andaman Earthquake

Abstract

We use several independent methods to estimate the radiated energy E_R of the Sumatra-Andaman earthquake (M_w=9.0 to 9.3), and investigate whether the difference in the rupture patterns between north and south is reflected in the difference in the energy budget. First, we used a finite source model and estimated E_R to be 1.38 x 10^(17) J for a frequency band f (frequency) ≤ 0.1 Hz. Since this method is relatively free from many assumptions commonly made in energy estimation, this value is considered robust. To estimate E_R for a frequency band 0.1 ≤ f ≤ 1 Hz, we used a frequency-domain analysis and obtained E_R = 1.6 x 10^(17) J for this frequency band. This estimate is somewhat uncertain because of the energy attenuation during propagation and the effect of the near-source structure. We also estimated E_R relative to the 2001 Bhuj, India, earthquakes for which a reliable estimate of E_R has been obtained. The total E_R thus estimated is 3.0 x 10^(17) J. The energy-moment ratio, 0.46 x 10^(-5), is slightly smaller than that for other large subduction-zone earthquakes. The radiation efficiency defined by η_R = (2µ /Δr)(E_R/M_0) (µ=rigidity, M_0=seismic moment, Δr =static stress drop) is 0.16 which is smaller than that of many large earthquakes, and is between the values of regular earthquakes and slow tsunami earthquakes. The values of η_R for the Nicobar segment, the Nicobar-Andaman segments combined, and the Sumatra segment are 0.053, 0.11, and 0.21, respectively, which suggests that the slip in the northern segments involves a large amount of energy dissipation associated with water-filled thick sediments.