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Residual Yakutat Microplate Velocity Drives Rapid Thrust Faulting North of the Central Denali Fault

Description: 

Plate convergence rates strongly influence seismicity and mountain building inboard of convergent margins, but the distribution and kinematics of structures accommodating far-field convergence can be elusive. In interior Alaska, Yakutat microplate convergence drives late Pleistocene–recent right-slip on the Denali Fault, but westward-decreasing slip rates leave substantial residual Yakutat motion unaccounted for. Here, we show that the Northern Foothills thrust slip accommodates a modern 4.4 mm/yr geodetic velocity gradient equivalent to ~78% of the total ~5.6 mm/yr residual Yakutat convergence along the central Denali Fault. Infrared-stimulated luminescence ages of strath terrace deposits (4–67 ka; 6 sites) quantify Totatlanika River bedrock incision across the 1947 M_w 7.1 thrust earthquake epicentral region. Incision rates increase northward abruptly from <1 mm/yr to 4.8–5.6 mm/yr across the range-front anticline overlying the blind thrust tip. Rapid 6.7 mm/yr slip on a steep thrust ramp modeled beneath the northern Alaska Range front accommodates the geodetic gradient, drives rock uplift at rates equivalent to measured incision rates, and implies that large earthquakes like the 1947 event may recur with 500–1400-yr frequency. Results illuminate focused seismogenic strain inboard of a complex convergent margin, and demonstrate that the pace of continental indentation in Alaska doubles prior expectations with direct implications for extant seismic hazard estimates.

Session: Cordilleran Strike-Slip Faults as Seismogenic and Seismological Features - I

Type: Oral

Date: 5/2/2024

Presentation Time: 05:00 PM (local time)

Presenting Author: Adrian

Student Presenter: No

Invited Presentation: 

Authors