Microseismic Evidence for Bookshelf Faulting in Western Montana
نویسندگان
چکیده
Abstract One of the most seismically active regions in United States, located hundreds kilometers inland from nearest plate boundary, is Intermountain Seismic Belt (ISB). The 6 July 2017 M 5.8 earthquake occurred 11 km southeast Lincoln, Montana, within ISB. This was largest to rupture state Montana since 1959 7.3 Hebgen Lake earthquake. We use continuous seismic data University Network, Regional and U.S. Geological Survey investigate Lincoln aftershock sequence evaluate crustal stress conditions. manually picked P- S-wave arrival times, computed 4110 hypocenter locations 2336 double-difference relocations, generated focal mechanisms for 414 aftershocks (12+ polarities) 2 yr following mainshock. Based on alignment aftershocks, we infer that mainshock a north–northeast-trending left-lateral strike-slip fault. orientation fault unexpected, given it strikes nearly perpendicular prominent Lewis Clark line (LCL) faults area. Although concentrate near mainshock, several distinct clusters microseismic activity emerge along subparallel primarily west also exhibit motion oblique LCL. postulate reveal clockwise rotation local-scale blocks about vertical axes larger, right-lateral shear zone. inferred block rotations are consistent with bookshelf-faulting mechanism, which likely accommodates differential north south LCL region. tension well-constrained indicate local northeast–southwest extension mean direction N60°E.
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ژورنال
عنوان ژورنال: Seismological Research Letters
سال: 2021
ISSN: ['0895-0695', '1938-2057']
DOI: https://doi.org/10.1785/0220200321