Bulletin of the Seismological Society of America
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Bulletin of the Seismological Society of America; January 2007; v. 97; no. 1A; p. S18-S24; DOI: 10.1785/0120050623
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The Energy Radiated by the 26 December 2004 Sumatra–Andaman Earthquake Estimated from 10-Minute P-Wave Windows

George L. Choy1 and John Boatwright2

1 U.S. Geological Survey
Box 25046, MS 966
Denver Federal Center
Denver, Colorado 80225
 (G.L.C.)
2 U.S. Geological Survey
Menlo Park, California 94025
 (J.B.)

The rupture process of the MW 9.1 Sumatra–Andaman earthquake lasted for approximately 500 sec, nearly twice as long as the teleseismic time windows between the P and PP arrival times generally used to compute radiated energy. In order to measure the P waves radiated by the entire earthquake, we analyze records that extend from the P-wave to the S-wave arrival times from stations at distances {Delta} >60°. These 8- to 10-min windows contain the PP, PPP, and ScP arrivals, along with other multiply reflected phases. To gauge the effect of including these additional phases, we form the spectral ratio of the source spectrum estimated from extended windows (between TP and TS) to the source spectrum estimated from normal windows (between TP and TPP). The extended windows are analyzed as though they contained only the P-pP-sP wave group. We analyze four smaller earthquakes that occurred in the vicinity of the MW 9.1 mainshock, with similar depths and focal mechanisms. These smaller events range in magnitude from an MW 6.0 aftershock of 9 January 2005 to the MW 8.6 Nias earthquake that occurred to the south of the Sumatra– Andaman earthquake on 28 March 2005. We average the spectral ratios for these four events to obtain a frequency-dependent operator for the extended windows. We then correct the source spectrum estimated from the extended records of the 26 December 2004 mainshock to obtain a complete or corrected source spectrum for the entire rupture process (~600 sec) of the great Sumatra–Andaman earthquake. Our estimate of the total seismic energy radiated by this earthquake is 1.4 x 1017 J. When we compare the corrected source spectrum for the entire earthquake to the source spectrum from the first ~250 sec of the rupture process (obtained from normal teleseismic windows), we find that the mainshock radiated much more seismic energy in the first half of the rupture process than in the second half, especially over the period range from 3 sec to 40 sec.




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S. L. Bilek, K. Satake, and K. Sieh
Introduction to the Special Issue on the 2004 Sumatra-Andaman Earthquake and the Indian Ocean Tsunami
Bulletin of the Seismological Society of America, January 1, 2007; 97(1A): S1 - S5.
[Full Text] [PDF]

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J. W. Dewey, G. Choy, B. Presgrave, S. Sipkin, A. C. Tarr, H. Benz, P. Earle, and D. Wald
Seismicity Associated with the Sumatra-Andaman Islands Earthquake of 26 December 2004
Bulletin of the Seismological Society of America, January 1, 2007; 97(1A): S25 - S42.
[Abstract] [Full Text] [PDF]


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