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Earth's Free Oscillations Excited by the 26 December 2004 Sumatra-Andaman Earthquake

2005; American Association for the Advancement of Science; Volume: 308; Issue: 5725 Linguagem: Inglês

10.1126/science.1112305

1095-9203

Jeffrey Park, Teh‐Ru Alex Song, Jeroen Tromp, Emile A. Okal, Seth Stein, G. Roult, E. Clévédé, G. Laske, Hiroo Kanamori, P. Davis, J. Berger, Carla Braitenberg, Michel Van Camp, Xiang’e Lei, Heping Sun, Houze Xu, S. Rosat,

Earthquake Detection and Analysis

At periods greater than 1000 seconds, Earth's seismic free oscillations have anomalously large amplitude when referenced to the Harvard Centroid Moment Tensor fault mechanism, which is estimated from 300- to 500-second surface waves. By using more realistic rupture models on a steeper fault derived from seismic body and surface waves, we approximated free oscillation amplitudes with a seismic moment (6.5 x 10(22) Newton.meters) that corresponds to a moment magnitude of 9.15. With a rupture duration of 600 seconds, the fault-rupture models represent seismic observations adequately but underpredict geodetic displacements that argue for slow fault motion beneath the Nicobar and Andaman islands.