HR: 08:30h
AN: T31C-03    [Abstracts]
TI: The joint seismic and geodetic inversion and strong ground motion estimates of the 2005 Nias 8.6 Earthquake
AU: * Konca, A O
EM: ozgun@gps.caltech.edu
AF: Tectonic Observatory, California Institute of Technology, Pasadena, CA 91125 United States
AU: Sieh, K
EM: sieh@gps.caltech.edu
AF: Tectonic Observatory, California Institute of Technology, Pasadena, CA 91125 United States
AU: Helmberger, D V
EM: helm@gps.caltech.edu
AF: Tectonic Observatory, California Institute of Technology, Pasadena, CA 91125 United States
AU: Avouac, J
EM: avouac@gps.caltech.edu
AF: Tectonic Observatory, California Institute of Technology, Pasadena, CA 91125 United States
AB: The largest known earthquakes have occurred on subducted plate interfaces mostly below water with very little direct measurements of motion. A few zones have islands just above these mega-thrust events affording GPS instrumentation and coral uplift data which recorded the recent Nias Earthquake (2005). Such a dataset provides the unique opportunity to study the rupture process and the generation of strong ground motions. Since we can rely on the GPS and field data to establish the geometry and static dislocations, we can use the seismic data to better constrain the temporal evolution of rupture more precisely by eliminating the trade-off between the rise time and slip off-sets. Our inversion results show that Nias earthquake is characterized by either slow rupture velocities (~2.5 km/s), or very long rise times (up to 30 seconds) or a combination of both. The slip pattern has two patches with a gap around the hypocenter region, which could be related to a tear in the slab, which is suggested from local geology. We estimate the peak ground velocity to be less than 30 cm/s at the largest GPS off-sets, an order of magnitude weaker than well-coupled continental events. These low estimates can be attributed to several factors; (1) distance away from the large slip elements (km) (2) relatively low stress drops (long rise times (30 s) and slow rupture velocities and (3) favorable directivity geometry which focuses energy into the ocean.
DE: 7203 Body waves
DE: 7215 Earthquake source observations (1240)
DE: 7240 Subduction zones (1207, 1219, 1240)
DE: 8170 Subduction zone processes (1031, 3060, 3613, 8413)
SC: Tectonophysics [T]
MN: Fall Meeting 2005