HR: 10:50h
AN: S12A-02    [Abstracts]
TI: Properties of fault slip in large earthquakes and its relation to aftershock distribution.
AU: * Das, S
EM: das@earth.ox.ac.uk
AF: Department of Earth Sciences, University of Oxford, Parks Road, Oxford, OX1 3PR United Kingdom
AB: From inversions of broad band body wave data to obtain the fault rupturing process and the moment distribution over the fault for several large earthquakes, together with accurate aftershock locations, we find that: 1. Ruptures generally nucleate in the region of low slip or at the edge of high slip regions, though a few exceptions are found, the most notable being the great 1996 Biak, Indonesia subduction zone earthquake. 2. No universal relation between high and low moment regions and high or low aftershock occurrence, or vice versa, is found. Generally fewer, and usually the smaller, aftershocks occur in the high slip regions. In his work on the characterization of fault barriers, Aki (JGR, 1979) suggested that most aftershocks should occur in the regions of little or no slip, and we found this to be generally true. The 1996 Biak earthquake is an exception. 3. The 1986 and the 1996 Andreanof Islands earthquakes are both believed to be ruptures of regions with little or no slip in the 1957 Rat Island earthquake, but their behavior with respect to the 1957 aftershocks is different (Das and Henry, Rev. Geophys., 2003) showing that even on adjacent portions of the same plate boundary the behavior can be different. 4. In all cases, aftershocks occur on favorably oriented planes of weakness in regions of increased post-seismic stress. 5. Aftershocks are generally, clustered at both ends of faults but examples where aftershocks occur only at one end or where there is no clustering at the ends are found. Aftershock clusters are also found at the edge of unbroken barriers, and regions of rapid transition from high to low slip, within the main fault area. 5. We identify examples of geometrical and inhomogeneous barriers, and sharp and dull stress concentrations. 6. Off-fault aftershocks are found for all earthquakes examined, and sometimes rupture the nodal plane conjugate to the main shock fault plane.
DE: 7230 Seismicity and seismotectonics
DE: 7209 Earthquake dynamics and mechanics
DE: 7215 Earthquake parameters
SC: Seismology [S]
MN: 2004 AGU Fall Meeting