Seismicity of the Denali-Totschunda Fault Zone in Central Alaska (1912-1988) and Its Relation to the 2002 Denali Fault Earthquake Sequence

Abstract

I have relocated M ≥ 4.5 earthquakes occurring between 1912 and 1988 and smaller magnitude earthquakes occurring between 1971 and 1988, when seismograph stations within central Alaska began to increase, to examine changes in seismicity preceding the 2002 Denali fault earthquake sequence. I have also determined focal mechanisms from first-motion analysis and waveform modeling for many of the M ≥ 5.5 events. Limited phase and waveform information for the 1912 M s 7.2 earthquake are consistent with rupture at shallow depth on a right-lateral strike-slip fault, although the limited data cannot distinguish between a range of possible mechanisms. Most other M ≥ 4.5 earthquakes occurring within the region prior to 1989 represent thrust/reverse faulting or strike-slip faulting adjacent to the Denali fault system. These results highlight the role thrust faulting plays in the deformation of the Denali region. Stress analysis shows continuity in the direction of maximum compressive stress ( σ 1 ) between the western Denali fault zone and the Castle Mountain fault/Upper Cook Inlet region, suggesting the crust is behaving rigidly to transfer compression to the Denali fault zone and faults located to the north.