Spatiotemporal analysis of the Foreshock-Mainshock-Aftershock sequence of the 6 July 2017 M5.8 Lincoln, Montana, earthquake
Seismological Research Letters
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Abstract
A MW 5.8 earthquake occurred on 6 July 2017 at 12.2 km depth, 11 km southeast of Lincoln in west central Montana. No major damage or injuries were reported; however, the widely felt mainshock generated a prolific aftershock sequence with more than 1200 located events through the end of 2017. The Lincoln event is the latest in a series of moderate-to-large earthquakes that have affected western Montana. We characterize the spatiotemporal evolution of the sequence using matched filter detection and multiple-event relocation techniques. Moment tensor solutions and aftershock locations indicate faulting occurred on a 9-km-long NNE-striking, near-vertical, strike-slip fault antithetic to the Lewis and Clark Line, the main through-going fault system. Seismicity primarily occurs between 6 and 16 km depth, consistent with seismicity in the Intermountain Seismic Belt. We estimate a fault rupture area of ~64 km2 and ~30 cm of average fault displacement. We identified four foreshocks in the three days prior to, and 3005 aftershocks in the three weeks following the mainshock. The supplemented catalog frequency-magnitude distribution has a b-value of 0.79 and a minimum magnitude of completeness of 0.7. The overall decay rate is consistent with a modified Omori decay law p-value of 0.76 and c-value of 0.32. This event demonstrates that unmapped faults antithetic to major geologic structures play a role in accommodating regional strain in Western Montana and can host significant earthquakes
Suggested Citation
McMahon, N., Yeck, W.L., Stickney, M.C., Aster, R.C., Martens, H.R., and Benz, H.M., 2019, Spatiotemporal analysis of the Foreshock-Mainshock-Aftershock sequence of the 6 July 2017 M5.8 Lincoln, Montana, earthquake: Seismological Research Letters, v. 9, no. 1, p. 131-139, https://doi.org/10.1785/0220180180.
ISSN: 1938-2057 (online)
Study Area
| Publication type | Article |
|---|---|
| Publication Subtype | Journal Article |
| Title | Spatiotemporal analysis of the Foreshock-Mainshock-Aftershock sequence of the 6 July 2017 M5.8 Lincoln, Montana, earthquake |
| Series title | Seismological Research Letters |
| DOI | 10.1785/0220180180 |
| Volume | 9 |
| Issue | 1 |
| Publication Date | November 07, 2018 |
| Year Published | 2019 |
| Language | English |
| Publisher | GSW |
| Contributing office(s) | Geologic Hazards Science Center |
| Description | 9 p. |
| First page | 131 |
| Last page | 139 |
| Country | United States |
| State | Montana |
| County | Lewis and Clark County |
| City | Lincoln |