Source Process of the November 3, 2002 Denali Fault Earthquake (Central Alaska)

The November 3, 2002 Denali fault earthquake which occurred along the arcuate segment of Denali fault, is the largest inland event ever recorded in central Alaska where oblique convergence between Pacific and North American plates is partitioned between subduction and right-lateral strike-slip motion. The rupture process of this event is examined by using the teleseismic body wave data collected by IRIS-DMC stations. The P-wave first motion polarities (FMP) indicate a substantial reverse component implying a change in focal mechanism during rupture. The inversion of P-waveforms using a finite fault source for fixed focal mechanisms also showed clear evidence for a significant reverse component at the beginning of the rupture that can not be fit with a vertical fault plane. The best fit to the overall waveforms are obtained by using a fault plane dipping to the north with an oblique component: (strike,dip,rake)=(290o,60o,155o) and results in a total seismic moment of of 5e1020 Nm (Mw = 7.7). We found that the rupture process can be divided into two subevents. During the initial subevent, rupture occurred near the hypocenter with a dominant reverse component and released a moment of 1.3e1020 Nm within 15 sec. After 10 sec, the second subevent (Mo = 3.7e1020 Nm) ruptured unilaterally to the east with an average rupture velocity of ~ 3.1 km/s and released most of the seismic moment along an energetic asperity located 160 km east of the hypocenter where the largest resolvable slip reaches up to 9 m. This subevent lasted for 100 sec with an almost pure strike-slip motion and ruptured a length >200 km. Using simplified rupture dimensions, we calculate average displacement as 5 m and average static stress drop as 7 MPa. Comparison of this event with similar magnitude 2001 Kunlun earthquake (Tibet) in terms of rupture length, number and location of aftershocks, amount of radiated seismic energy, static stress drop and tectonic setting; implies stronger seismic coupling along the Denali fault than the Kunlun fault.