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Deciphering Low-Rate Faulting on the Landscape Above the Marsh Creek Anticline in Arctic Alaska

Description: 

In regions of rapid contractional deformation (≥1 mm/a), rivers adjust to earthquake-induced differential rock uplift by steepening, narrowing, and/or incising terraces. Such landscape signatures constrain the location and millennial tempo of active faulting but may be subdued or absent where tectonic rates are low. Hence, understanding how rivers interact with low-rate tectonic deformation is key to characterizing long-term seismic potential where strong earthquakes are infrequent but nonetheless destructive. For example, ~1000 km north of the 53 mm/a Yakutat-North America collision at Alaska’s southern margin, the northeastern Brooks Range hosts low geodetic velocities (<1 mm/a) but strong historic earthquakes (≤M_w 6.4). There, we are conducting a geomorphic study of a composite structure long thought to take up much of the contemporary tectonic budget and termed the Marsh Creek anticline.

Topographic profiles reveal a north-dipping limb with ~100 m of relief, implying monoclinal surface folding above a north-dipping blind thrust fault imaged in seismic reflection data. The Katakturuk River and Marsh Creek drain the Brooks Range upstream of the fold and traverse the structure’s topographic crest on the Arctic Coastal Plain, where both rivers cut ≤60 m into weak Paleogene strata and bend ≤3 km west, leaving three inner bend fill terrace levels ≤16 m above the channel. Absent downstream changes in channel slope or width, we hypothesize that episodic differential uplift across the Marsh Creek structure reduces river gradients upstream of the fold, driving aggradation of coarse bedload from upstream and forcing the channel to erode westward and vertically into friable Paleogene strata, thus producing river bends and progressively abandoning fill terraces. We collected cosmogenic ¹⁰Be samples to constrain erosion rates upstream of the fold and, in concert with ¹⁴C and luminescence dating, bracket timing of terrace abandonment and incision rates. Results will test our hypothesis that the observed landscape records sediment production upstream of the fold that outpaces earthquake-induced incision.

Session: Cryptic Faults: Advances in Characterizing Low Strain Rate and Environmentally Obscured Faults - I

Type: Oral

Date: 5/1/2024

Presentation Time: 08:45 AM (local time)

Presenting Author: Adrian

Student Presenter: No

Invited Presentation: 

Authors