HR: 0800h
AN: S41A-0958    [Abstracts]
TI: RADIATED SEISMIC ENERGY DETERMINED FROM A SPONTANEOUS RUPTURE MODEL OF THE 1994 NORTHRIDGE EARTHQUAKE
AU: * Ma, S
EM: sma@crustal.ucsb.edu
AF: Department of Geological Sciences, University of California, Santa Barbara, Santa Barbara, CA 93106 United States
AU: Archuleta, R
EM: ralph@crustal.ucsb.edu
AF: Department of Geological Sciences, University of California, Santa Barbara, Santa Barbara, CA 93106 United States
AU: Archuleta, R
EM: ralph@crustal.ucsb.edu
AF: Institute for Crustal Studies, University of California, Santa Barbara, Santa Barbara, CA 93106 United States
AB: The radiated seismic energy of the 1994 Northridge earthquake (M 6.7) is calculated by simulating a spontaneous rupture model of the earthquake in a layered velocity structure. Using a static finite element method the stress drop distribution is determined from the inverted slip distribution (Liu and Archuleta, 2000). From the stress drop distribution we derive a spatially heterogeneous initial stress and yield stress. In concert with a slip-weakening friction law we dynamically rupture the fault using a 3D finite-element method. By using trial and error we modified both the initial stress field and yield stress until dynamic rupture generated a rupture history and final slip distribution that approximately matched those determined by kinematic inversion. The resulting dynamic model provides a reasonably good fit between synthetics and near-field strong motion data. The total radiated seismic energy calculated from our dynamic model is 7.89 x 1014 J, which is close to the Gutenberg-Richter estimate of 7.08 x 1014 J. By displaying the energy distribution on a 40 km radius hemisphere enclosing the source, strong directivity effects are evident: 35.83 percent of the seismic energy passes through 8.92 percent of the whole hemisphere area, most of which is concentrated in the forward direction of the rupture. Energy passing through the bottom of the sphere, i.e., the energy radiated to teleseismic distances, is very small.
DE: 7847 Radiation processes
DE: 7209 Earthquake dynamics and mechanics
DE: 7212 Earthquake ground motions and engineering
DE: 4255 Numerical modeling
DE: 2487 Wave propagation (6934)
SC: Seismology [S]
MN: 2004 AGU Fall Meeting