HR: 1340h
AN: T33B-0548    [Abstracts]
TI: Highly Resolved Kinematic Fault Models of Two Nankai Trough Earthquakes Derived From Tsunami Waveforms
AU: * Baba, T
EM: babat@jamstec.go.jp
AF: IFREE/JAMSTEC, 3173-25, Showa-machi, kanazawa-ku, Yokohama, 236-0001 Japan
AU: Cummins, P R
EM: phil.Cummins@ga.gov.au
AF: Geoscience Australia, GPO Box 378, Canberra, ACT 2601 Australia
AB: We have developed a new method for inverting tsunami waveforms that reveals considerable detail in megathrust slip during subduction zone earthquakes. Previous methods have ensured compliance with the shallow-water theory used to compute tsunami waveforms by using large subfaults that generate only long-wavelength seafloor deformation. We show that a better approach is to use small subfaults coupled with a smoothing criterion that ensures compliance with the shallow-water approximation. In an application of the method to the 1944 Tonankai and the 1946 Nankai earthquakes which ruptured adjacent segments of the Nankai subduction zone, southwestern Japan, we found positive correlation between the rupture patterns and crustal structure. The considerable slip near the trench of the 1944 slip model that appears off Kii Peninsula is in good agreement with the spatial extent of a splay fault branching from the plate boundary. A subducting seamount beneath the accretionary prism off Cape Muroto and Deep Strong Reflectors near the trench coincide with areas of low slip in the rupture models. Furthermore, the most interesting feature in our model is that the areas with slip more than 1 m for the earthquakes of 1944 and 1946 are separated by a sharp, non-overlapping boundary. This establishes that interseismic accumulation of strain energy extends very close to the boundary between rupture zones, and strongly suggests that this boundary is associated with a hidden physical barrier to rupture. In some other subdcution zones, several studies have shown that significant slip was centered in areas that experienced low slip in the previous event, suggesting that the slip pattern varies markedly for earthquakes which sequentially rupture a given subduction zone segment. However, at the Nankai trough, the features of our slip models described here support the alternate hypothesis that slip distributions of subduction zone earthquakes should be similar to the previous earthquake since crustal structure has an important effect on either megathrust rupture propagation or the interseismic accumulation of elastic strain, or both.
DE: 4564 Tsunamis and storm surges
DE: 7209 Earthquake dynamics (1242)
DE: 8123 Dynamics: seismotectonics
DE: 8170 Subduction zone processes (1031, 3060, 3613, 8413)
SC: Tectonophysics [T]
MN: Fall Meeting 2005