HR: 10:50h
AN: S11H-03    [PDF]
TI: Source Process of the M7.9 Denali Fault, Alaska, Earthquake: Sub-Events, Directivity, and Scaling of High-Frequency Ground Motion
AU: * Frankel, A
EM: afrankel@usgs.gov
AF: U.S. Geological Survey, MS 966, Box 25046, DFC, Denver, CO 80225
AB: Analysis of strong-motion recordings of the Nov. 3, 2002 M7.9 Denali Fault earthquake from distances of 3-300 km shows the complexity of this large event and the scaling of high-frequency ground motion. Waveform modeling indicates that the earthquake started with an approximately east-west striking thrust sub-event, corresponding to the surface rupture observed along the Susitna Glacier fault. I inverted the strong-motion waveforms after the first sub-event to determine the slip as a function of space and time along the Denali and Totschunda faults. The inversion result contains two strike slip sub-events along the Denali fault centered about 80 and 190 km east of the hypocenter. The first strike-slip sub-event was centered on the Denali fault across from the instrument at Pump Station 10 and occurred near a releasing bend in the fault. The second strike-slip sub-event occurred just to the west of the junction of the Denali and Totschunda faults and had the largest moment release. These areas of high slip correspond to locations of large slip found from geodetic data and surface offsets. The preferred inversion solution entails a fast rupture velocity of about 3.5 km/sec between the two strike-slip sub-events, which is close to the shear-wave velocity at depth. Rupture directivity caused large differences in waveforms for stations at varying azimuths. I compared acceleration spectra of the strike-slip portion of the M7.9 Denali Fault earthquake with those of the adjacent M6.7 Nenana Mountain earthquake recorded at the same sites. The high-frequency spectral amplitude ($>$ 0.5 Hz) of the M7.9 earthquake is somewhat less than expected from a scaling relation where the energy radiated at any given frequency is proportional to the fault area, which is the high-frequency scaling relation typically observed for smaller earthquakes.
DE: 7209 Earthquake dynamics and mechanics
DE: 7212 Earthquake ground motions and engineering
DE: 7215 Earthquake parameters
DE: 7223 Seismic hazard assessment and prediction
SC: Seismology [S]
MN: 2003 Fall Meeting