Surface Rupture and Slip Distribution of the Denali and Totschunda Faults

The 3 November 2002 Denali fault, Alaska, earthquake resulted in
341 km of surface rupture on the Susitna Glacier, Denali, and Totschunda faults. The
rupture proceeded from west to east and began with a 48-km-long break on the
previously unknown Susitna Glacier thrust fault. Slip on this thrust averaged about
4 m (Crone et al., 2004). Next came the principal surface break, along 226 km of
the Denali fault, with average right-lateral offsets of 4.5–5.1 m and a maximum offset
of 8.8 m near its eastern end. The Denali fault trace is commonly left stepping and
north side up. About 99 km of the fault ruptured through glacier ice, where the trace
orientation was commonly influenced by local ice fabric. Finally, slip transferred
southeastward onto the Totschunda fault and continued for another 66 km where
dextral offsets average 1.6–1.8 m. The transition from the Denali fault to the Totschunda
fault occurs over a complex 25-km-long transfer zone of right-slip and
normal fault traces. Three methods of calculating average surface slip all yield a
moment magnitude of Mw 7.8, in very good agreement with the seismologically
determined magnitude of M 7.9. A comparison of strong-motion inversions for moment
release with our slip distribution shows they have a similar pattern. The locations
of the two largest pulses of moment release correlate with the locations of
increasing steps in the average values of observed slip. This suggests that slipdistribution
data can be used to infer moment release along other active fault traces.