PROGRESS IN CHARACTERIZING ACTIVE FAULTS OF THE NORTHERN FLANK OF THE ALASKA RANGE

Surveys of offset and deformed geomorphic features and a paleoseismic trench across several active faults along the northern flank of the Alaska Range, combined with previous structural mapping, allow us to constrain the geometry and slip rates for these faults. As a reconnaissance investigation, we surveyed moraines offset by the Canteen fault, two sets of stream terraces; one that is deformed across the Northern Foothills thrust, another within the Eight-Mile Lake syncline, and dug a paleoseismic trench across the Healy fault. The Canteen fault is one of a series of parallel, NE-striking left-lateral faults that offset the northern range front of the eastern Alaska Range. Offset moraines indicate a slip rate of 1-2 mm/yr on this structure. The Northern Foothills thrust and Eight-Mile Lake syncline are prominent structures of the Northern Foothills fold-and-thrust belt of the central Alaska Range. The Healy fault is interpreted as a flexural-slip fault related to active folding of the Eight-Mile Lake syncline. Profiles of the stream terraces provide constraints on the geometry of the Northern Foothills thrust and faults related to folding of the Eight-Mile Lake syncline, which will allow us to calculate slip rates with improved age control. Ongoing paleoseismic work on the Healy fault suggests multiple fault ruptures during the past 20 k.y. These results show that these are active faults, and suggest other faults along the northern flank of the Alaska Range are active as well. Thus, this study provides important information for a complete seismic hazard assessment of interior Alaska and demonstrates there is clear geologic evidence justifying further research in characterizing potential seismogenic structures in the Alaska Range.