Browsing by Author "Choi, Minhee"

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    Source Parameters and Tectonic Setting of the 2017 St. Elias Earthquake Sequence near the Southern Terminus of the Eastern Denali Fault, Northwestern Canada
    (2019-09-18) Choi, Minhee; Eaton, David W. S.; Enkelmann, Eva; Dettmer, Jan; Gilbert, Hersh J.
    On May 1, 2017 two earthquakes of magnitude 6.2 and 6.3, respectively, occurred in proximity to the eastern Denali fault (EDF). These double mainshock events were followed by more than 2,700 aftershocks. Moment-tensor inversion of the mainshock signals shows that the initial event produced reverse slip on a steeply dipping fault with a NW-SE strike direction, while the second produced left-lateral strike-slip on a near-vertical fault with an E-W strike direction. A double-difference relocation method, coupled with clustering analysis, was applied to the aftershock distribution, confirming that seismicity was localized along two previously unmapped fault structures. Stress inversion indicates that the maximum principal stress axis is oriented almost perpendicular to the EDF, suggesting that the fault system is not well oriented for strike-slip in the contemporary stress field. Coulomb stress analysis indicates that the second event was likely triggered by the first one (static stress triggering), with a delay of about two hours. A generalized model is developed to explain the observations, wherein gravitational potential from the >4,000 m high Mount Fairweather, as well as strain partitioning along the plate boundary, produce a stress regime that extends inboard towards the EDF.