Rupture Process of the M7.9 Denali Fault, Alaska, Earthquake Determined from Strong-Motion Recordings

We have analyzed and modeled strong-motion recordings available to date of the M7.9 Denali Fault earthquake of November 3, 2002. The data are from instruments at epicentral distances of 60-290 km operated by the USGS National Strong Motion Network, the Advanced National Seismic System, and the Geophysical Institute of the University of Alaska. We have identified and located three major sub-events of the earthquake using the displacement waveforms from these stations. The first sub-event occurred near the hypocenter and waveform modeling of the strong-motion records indicates that it is characterized by thrust faulting on a fault striking east-northeast. The second sub-event is centered about 70-80 km east of the hypocenter and is dominated by right lateral strike-slip motion. This sub-event is located in the area where substantial strike slip surface offset is observed. The third sub-event, clearly observed only at Valdez, is centered approximately 170 km east of the hypocenter, based on a rupture velocity of 3 km/sec. This is the approximate location of the largest surface displacements. At Valdez, which is equidistant from the three sub-events, the largest accelerations are associated with the first two sub-events. Peak acceleration values for the available stations were modest: about 10%g for portable stations 60-70 km west of the hypocenter, 9%g for Fairbanks about 150 km from the hypocenter, and about 2%g or less for Anchorage at about 280 km hypocentral distance. At the meeting, we will show an animation of ground motions recorded by stations across Anchorage.