Denali fault - Dead Mouse site

During field studies in the Alaska Range in the summer of 2012, with fresh airborne lidar data in hand, Patrick Taylor and I found a surprising thickness of fine-grained sediment on a low fluvial terrace next to where the Denali fault crosses the Nenana River. Patrick took on the initial reconnaissance paleoseismic trenching at this site as an undergraduate project, presenting his preliminary work at AGU in 2012. I used the results of this initial investigation as the basis for a proposal that was funded by the USGS-NEHRP program (Award #G14AP00134), and returned in the summer of 2015 to document this site more extensively. Kade Carlson took on this project for his MS thesis at the University of Kentucky, and we were assisted in this work by Nathan Toke (Utah Valley U.) and Brad Bishop (BYU). The results are published here (PDF).

In summary, we documented evidence for 7 prehistoric surface rupturing during the past ~7000 years. However, we only consider the sequence of the most recent 4 earthquakes to be complete; intervals between the oldest three earthquakes exhibit unconformities and limited stratigraphic control and those gaps likely contain additional earthquakes.

With the site being inaccessible for heavy equipment, we excavated our trenches 'by hand' (#artisanalpaleoseismology). The fine-grained fluvial and aeolian sediments at this position near the crest of a terrace riser are only seasonally frozen, making them relatively easy to excavate and clean up into smooth, continuous exposures.

With limited space to excavate across the fault trace, we had to get creative with our trenches to dodge trees while seeking to expose the full width of the fault zone. Additional excavations at the site could improve of some of the paleoearthquake constraints of Carlson et al. (2018), but the presence of unconformities and an increase in cryoturbation to the east significantly limits this possibility.