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Confirmation of Late Quaternary Surface Faulting and Preliminary Slip Rates for the Iditarod-Nixon Fork Fault and the Boss Creek and Holitna Sections of the Denali Fault in West-Central Alaska

Description: 

The Iditarod Nixon Fork fault (INFF) and the Boss Creek and Holitna sections of the Denali fault (BCF and HF) in west-central Alaska are included as Quaternary faults in active fault databases and as crustal fault sources in the USGS 2023 Alaska Seismic Hazard Model. Information about the activity of these structures and their associated seismic hazard parameters (i.e. slip rate, recurrence, geometry) is sparse due to a lack of detailed studies. We evaluated these faults to address uncertainties and data gaps as part of a seismic source characterization for the Donlin Gold Project. The study included lidar collection along 130 km of the INFF, desktop geomorphic mapping and criteria-based evaluation of faults and lineaments within 100 km of the Project site, aerial and ground-based reconnaissance of prioritized faults and lineaments, and collection of 14C, ¹⁰Be TCN, IRSL, and tephra samples to constrain ages of displaced surfaces and estimate slip rates for the INFF, BCF, and HF.

Along the INFF, our mapping and reconnaissance confirmed strong geomorphic evidence of late Quaternary faulting extending southwest of Moore Creek, AK, for 100 to 125 km. Right-lateral slip along the INFF has displaced tributaries of Bonanza Creek 18±6m. Using IRSL ages of ~32-38 ka and ~22-23 ka from two loess deposits that mantle the faulted surfaces, we estimate a preliminary maximum slip rate of ~0.5-1 mm/yr. Geomorphic evidence of Quaternary faulting is weak to absent for an additional 75 to 100 km of the fault extending southwest to the Kuskokwim River. Along the Denali fault, 14C ages from a test pit in an abandoned Holitna River channel confirms at least one surface rupture in the past ~1000 years, consistent with the presence of en-echelon fissures in muskeg at Itulilik Creek. Four ¹⁰Be TCN ages from boulders on a displaced LGM moraine complex (20-23 ka) will be combined with offset reconstructions to estimate preliminary slip rates at the junction of the BCF and HF. These findings confirm significantly more Holocene slip farther west on the Denali fault than previously estimated.

Session: From Faults to Fjords: Earthquake Evidence in Terrestrial and Subaqueous Environments - III

Type: Oral

Date: 5/1/2024

Presentation Time: 02:30 PM (local time)

Presenting Author: Mark

Student Presenter: No

Invited Presentation: 

Authors