The Energy Radiated by the 26 December 2004 Sumatra–Andaman Earthquake Estimated from 10-Minute P-Wave Windows

Abstract

The rupture process of the M W 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 D Ͼ60Њ. 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 T P and T S ) to the source spectrum estimated from normal windows (between T P and T PP ). 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 M W 9.1 mainshock, with similar depths and focal mechanisms. These smaller events range in magnitude from an M W 6.0 aftershock of 9 January 2005 to the M W 8.6 Nias earthquake that occurred to the south of the SumatraAndaman 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 (ϳ600 sec) of the great Sumatra-Andaman earthquake. Our estimate of the total seismic energy radiated by this earthquake is 1.4 ‫ן‬ 10 17 J. When we compare the corrected source spectrum for the entire earthquake to the source spectrum from the first ϳ250 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.

The 25 October 2010 Mentawai tsunami earthquake, from real-time discriminants, finite-fault rupture, and tsunami excitation

“…By the fourth iteration, 16.5 minutes after the rupture began, RTerg stabilized to its near final solution with T R = 126 s and M e = 7.09. A final determination was made after an analyst reviewed the event, and corrected for the reported global Centroid Moment Tensor (gCMT) focal mechanism [ Ekström et al , 2005], finding T R = 127 s and M e = 7.03 using 51 stations, comparable but smaller than the final result determined independently by the USGS ( M e = 7.2) [ Choy and Boatwright , 2007].…”

Apparent stress scaling for tectonic and induced seismicity: Model and observations

“…For comparison, 4 tsunami earthquakes are considered: Peru, 1996, Nicaragua, 1992, Java 1994(Ihmlé, 1996Ihmlé et al, 1998;Bilek et al, 2004) and the Sumatra-Andaman 2004 destructive event (Choy and Boatwright, 2007;Sørensen et al, 2007;Banerjee et al, 2007).…”

Introduction to the Special Issue on the 2004 Sumatra–Andaman Earthquake and the Indian Ocean Tsunami

“…Because the duration of the P wave is long enough to include later arrivals, some standard methods for energy calculations will fail to produce an accurate estimate. Choy and Boatwright (2007) demonstrate that an extension of the empirical Green's function method can be used to estimate the radiated energy for a great earthquake such as this one. The authors correct for the later-phase arrivals by using a modified empirical approach that produces a value of radiated energy (E s ) of 1.4 ‫ן‬ 10 17 J.…”