HR: 13:30h
AN: U43A-01 INVITED     [Abstracts]
TI: Source characteristics of the great Sumatra earthquake and its aftershocks
AU: * Nettles, M
EM: nettles@eps.harvard.edu
AF: Department of Earth and Planetary Sciences, Harvard University, 20 Oxford Street, Cambridge, MA 02138
AU: Ekström, G
AF: Department of Earth and Planetary Sciences, Harvard University, 20 Oxford Street, Cambridge, MA 02138
AU: Dziewoński, A M
AF: Department of Earth and Planetary Sciences, Harvard University, 20 Oxford Street, Cambridge, MA 02138, United States
AU: Maternovskaya, N
AF: Department of Earth and Planetary Sciences, Harvard University, 20 Oxford Street, Cambridge, MA 02138, United States
AB: Rapid centroid-moment-tensor (CMT) analysis of the December 26, 2004, Sumatra earthquake in the period range 300--500~s gave a seismic scalar moment of 4×10²⁹~dyne-cm (M_W~9.0). The strike, dip, and rake of the presumed fault plane were found to be 329°, 8°, and 110°, respectively. The centroid location was determined to be 3.1°N, 94.3°E, and the centroid depth 29~km. The centroid time shift was found to be ~140~s. Surface-wave directivity indicates rupture toward the northwest, consistent with the locations of aftershocks occurring in the first month following the mainshock. We present further analysis of the mainshock source characteristics, including evaluation of the possibility that the total moment and source duration were significantly larger than those determined in our rapid CMT analysis. We also present focal-mechanism solutions for aftershocks having moment magnitudes M_W~5.0 and larger. A large number of these aftershocks occurred during an unprecedented earthquake swarm east of the Nicobar Islands. The swarm began one month after the mainshock, on January 26, 2005. We detected more than 150 earthquakes of M~5.0 or larger during a period of three days, more earthquakes of this size than normally occur globally during a two-week period. The centroid locations of the earthquakes comprising the swarm are tightly clustered, lying within a radius of ~30~km. These earthquakes show strike-slip and normal faulting, with axes of maximum tension oriented northwest--southeast.
DE: 7200 SEISMOLOGY
DE: 7215 Earthquake parameters
SC: Union [U]
MN: 2005 Joint Assembly