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Steps Toward Linking the Kaltag and Tintina Faults in Interior Alaska

Description: 

Alaska tectonics are driven by subduction of the Pacific Plate beneath the North American Plate at the state’s southern border, causing N–S compression and shearing of southern Alaska to the west. Transpression and rotation occur over 700 km north of the subduction trench in Interior Alaska, where the Kaltag–Tintina fault system, a north-convex right-lateral strike-slip arch, spans the entire state. The Tintina fault is a westward extension of a major tectonic strike valley in Canada, and both it and the Kaltag fault are characterized by linear scarps, slope breaks, swales, and right-lateral offset streams. Slip rate estimates for the system range from 0.01 to <0.5 mm/yr, suggesting interseismic periods of thousands to tens of thousands of years and contributing to poor preservation of past activity and large uncertainty in seismic potential. Despite geomorphic expression, diffuse seismicity, and several recent M4–5 events, documented Quaternary activity along the two faults is sparse and the link between the two faults near the Yukon River Bridge—economically crucial infrastructure—is poorly understood. Ongoing work with new statewide high-resolution imagery and elevation datasets suggests that the W–NW striking Tintina fault system bends to the W–SW around Mt. Schwatka. West of Mt. Schwatka, DGGS collected high-resolution lidar that confirms disappearance of young deformation into the linear Rogers and Isom creek valleys near the Yukon River. However, farther W–SW along strike in the southern Ray Mountains, lidar elevation models reveal ~25 km of youthful surface rupture, the western end of which represents a ~35 km left step at the mapped end of the Kaltag fault at Tanana. These newly discovered faults suggest a M6.5 paleoearthquake ~50 km SW of the Yukon River Bridge. Though the first attempt at traditional paleoseismic trenching was inconclusive, lidar and field mapping illustrate the variability in geomorphic preservation of fault activity over short distances and highlight the difficulty in properly characterizing seismic hazard for low strain rate faults in forested, high-latitude terrain.

Session: Cryptic Faults: Advances in Characterizing Low Strain Rate and Environmentally Obscured Faults [Poster Session]

Type: Poster

Date: 5/1/2024

Presentation Time: 08:00 AM (local time)

Presenting Author: Barrett

Student Presenter: No

Invited Presentation: 

Authors