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Potential megathrust co-seismic slip during the 2020 Sand Point, Alaska strike-slip earthquake
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  • Sean R Santellanes,
  • Diego Melgar,
  • Brendan W Crowell,
  • Jiun-Ting Lin
Sean R Santellanes
University of Oregon, University of Oregon

Corresponding Author:[email protected]

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Diego Melgar
University of Oregon, University of Oregon
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Brendan W Crowell
University of Washington, University of Washington
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Jiun-Ting Lin
University of Oregon, University of Oregon
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Abstract

On October 2020, a Mw 7.6 earthquake struck to the south of the Shumagin Islands in Alaska, nearly 3 months after the Mw 7.8 Simeonof megathrust event. The initial models of the earthquake indicated a largely strike-slip rupture; however, the observed tsunami was much larger and widespread than expected for the focal mechanism. We investigate what sea surface deformation is necessary to recreate the tsunami waveforms using water-level inversion techniques. We find that the sea surface deformation does not resemble that expected from a purely strike-slip earthquake. We then carry out slip inversions with water level and static GNSS data as input. We explore the likelihood of megathrust co-seismic slip aiding tsunamigenesis. We propose that, concurrently with strike-slip faulting, it is likely that a considerable slip occurred on the megathrust westward and updip from the previous July 2020 event. We also propose that a smaller submarine landslide is likely to have occurred in an area prone to them. The Sand Point earthquake potentially released ~2 meters of accumulated slip in the western Shumagin Gap, but likely did not slip updip of ~15 km depth.