HR: 13:40h
AN: S33C-01    [Abstracts]
TI: Near-Compressional Wave Rupture Speed Detected for the November 14, 2001 M_w 7.8 Kunlun Earthquake
AU: * Das, S
EM: das@earth.ox.ac.uk
AF: Department of Earth Sciences, University of Oxford, Parks Road, Oxford, OX1 3PR United Kingdom
AU: Robinson, D P
EM: davidr@earth.ox.ac.uk
AF: Department of Earth Sciences, University of Oxford, Parks Road, Oxford, OX1 3PR United Kingdom
AB: This was one of the largest earthquakes to have occurred on land in the last 30 years, its mapped surface rupture being ~450 km. Analysis of surface waves have indicated super-shear rupture may have occurred on the fault. We relocate the aftershocks of this earthquake using the method of Joint Hypocenter Determination (JHD). Next, we re-calculate the Centroid Moment Tensor (CMT) solution using mantle wave data, and find a solution (strike 94°, dip 70°, rake -25°) in close agreement with that found by Harvard. We then impose a pure-double couple (PDC) constraint, and find that this alters the solution obtained (strike 98°, dip 90°, rake -36°), without significantly altering the fit to the data. Finally, we invert broadband SH data, using the method of Das and Kostrov (JGR 1990; Phys. Earth Planet. Int. 1994), to resolve details of the rupture history. We find that we need two faults and a depth extent of 20 km to fit the data. Rupture velocity was variable during the earthquake, beginning with sub-shear velocity rupture propagation of ~3.3 km/s (94% of shear wave speed, v_s) for the first ~120 km. The rupture then continued propagating eastwards for another ~150 km at an average speed approaching ~6 km/s, the local compressional wave speed. For the final ~130 km, the rupture propagated at ~4.1 km/s (115% of v_s). The region of high rupture velocity coincides with the region of highest fault slip. The highest concentration of aftershocks is located ~200-300 km east of the hypocenter, where the fault velocity decreases from near-compressional to super-shear, and the fault bifurcates. Our results have important implications for seismic hazard assessment and fundamentals of earthquake fracture mechanics.
DE: 7209 Earthquake dynamics (1242)
DE: 7215 Earthquake source observations (1240)
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
SC: Seismology [S]
MN: Fall Meeting 2005