Coseismic Deformation of the 2018 Kaktovik Earthquakes Illuminate Active Tectonics in Alaska’s Brooks Range

Date: 4/24/2019

Time: 06:00 PM

Room: Grand Ballroom

The M6.4 and M6.0 August 8^th 2018 Kaktovik earthquakes occurred in the northeastern Brooks Range, ~80 km SW of Kaktovik, Alaska. Despite northern Alaska being seismically active, the tectonics of this area remain enigmatic due to its remote location. However, Sentinel-1 satellite radar imagery captured the coseismic ground deformation of the M6.4 event and the M6.0 aftershock, the largest-magnitude earthquakes ever recorded in the Brooks Range and North Slope, providing an opportunity to investigate regional tectonics. We use Sentinel-1 InSAR data and elastic modelling, calibrated main shock and aftershock relocations, and a seismic back-projection to characterize the fault geometry and rupture process of the Kaktovik earthquakes. Our InSAR models show that the rupture occurred on a roughly E-W right-lateral fault in the Sadlerochit Mountains, composed of two distinct south-dipping fault segments. The rupture initiated on the western sub-vertical pure right-lateral fault segment, and propagated onto the shallower-dipping (63°) oblique (dextral-normal) fault segment to the east. The rupture likely did not reach the surface, with slip concentrated between depths of 4 and 8 km. Notably, the location of the fault indicated by the InSAR data suggests the reactivation of a previously identified south-dipping Paleogene thrust fault east of the conjugate NNE-SSW left-lateral Canning Displacement Zone. The E-W right-lateral faults that ruptured in the Kaktovik earthquakes could accommodate NNE-oriented left-lateral shear by rotating about vertical axes through time, in a pattern similar to that observed in some other continental belts. The Kaktovik earthquakes thus demonstrate the potential for large-magnitude earthquakes in the Brooks Range and the presence of unknown active faults whose kinematics may be influenced by inherited geological structures.

Presenting Author: Élyse Gaudreau

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