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Test of the Preshock Accelerating Moment Release (AMR) in the Case of the 26 December 2004 M_w 9.0 Indonesia Earthquake

¹ Institute of Geophysics
China Earthquake Administration
Beijing 100081, China
 (C.S.J., Z.L.W.)

² College of Earth Science
Graduate University of Chinese Academy of Sciences
Beijing 100049, China
wuzhl{at}gucas.ac.cn
 (Z.L.W.)

A case study of the 26 December 2004 M_w 9.0 earthquake off the west coast of northern Sumatra, Indonesia, was conducted to explore whether there was a preshock accelerating moment release (AMR) process for the intermediate timescale. The Harvard CMT catalog was used to calculate the cumulative moment tensor directly, with clearer physical significance with regard to the deformation prior to the great earthquake. We observed that average moment tensors at different times over the last decade before the great earthquake are consistent, and are similar to the focal mechanism of the great earthquake. However, the widely used cumulative scalar seismic moment and cumulative Benioff strain are only an approximation of the preshock deformation. To test the robustness of the accelerating property with respect to the selection of spatiotemporal parameters, we calculated the scaling coefficient m for different spatiotemporal ranges. The curvature parameter q was used to quantify the difference between the power-law fit and the linear fit to ensure the statistical significance of the power-law-like accelerating behavior. Grid searching over the (t_f, m) space was conducted to explore the global stability of the solution. The result showed that there existed a reliable preshock AMR process before this great earthquake, with duration of a quarter of a century and a spatial range from 800 to 1500 km, providing seemingly positive evidence for the AMR model. However, the failure time t_f was not well constrained by the AMR analysis, and the AMR model may be problematic for a longer timescale.