HR: 14:15h
AN: U43A-04    [Abstracts]
TI: Rupture Process of the Great Sumatra-Andaman Earthquake
AU: Ammon, C J
EM: cammon@geosc.psu.edu
AF: Penn State, 440 Deike Building, University Park, PA 16802 United States
AU: Velasco, A
EM: velasco@geo.utep.edu
AF: University of Texas El Paso, Department of Geological Sciences, El Paso, TX 79902 United States
AU: * Lay, T
EM: tlay@es.ucsc.edu
AF: UC Santa Cruz, Earth Sciences Department, Santa Cruz, CA 95064 United States
AB: We are using Rayleigh waves with periods between 100 and 500 seconds to map seismic moment release during the Mw 9.3 Sumatra-Andaman earthquake along the northern Indonesian subduction zone. To isolate source effects from the observed waveforms we deconvolved normal-mode synthetic seismograms computed using PREM and the Harvard CMT mechanism located at the USGS-NEIC epicenter. We obtain about 200 useable R1 source time functions with a good azimuthal distribution, admittedly more densely sampled to the north. Our preliminary results suggest that the major normal seismic moment release began about one minute after the initial slip (identified by the USGS-NEIC origin time) and then continued for about 400-450 additional seconds. Using observed source time functions for stations located perpendicular to the rupture direction and assuming a rupture velocity of 2.5 km/s, we estimate that the average slip along a width of about 150 km is on the order of 10 to 20 meters along much of 1250-km long rupture zone. Still, although the total moment associated with this slip equals that of the Harvard CMTsolution, it underestimates longer-period moment estimates by about a factor of three. We used an inverse Radon Transform (IRT) to extract rupture constraints from the azimuthal variations of the available source time functions. The IRT approach limits us to constraining first-order moment-release variations along the rupture strike but allows complete freedom to the temporal release of moment (i.e. no prescribed rupture velocity). Initial IRT results suggest relatively normal seismic moment release from near the hypocenter stretching at least 800 km northward. The initial minute of rupture appears to be slow (but within our resolution this could reflect been a hesitation in rupture). The long-period duration of 800 seconds (J. Park) and the substantially larger moment (S. Stein and E. Okal) suggest that at least 2/3 of the moment was released very slowly and predominantly influenced waves with periods greater than about 500 seconds. The location of this missing moment is an intriguing first-order problem associated with this very large earthquake.
DE: 7215 Earthquake parameters
SC: Union [U]
MN: 2005 Joint Assembly