The March 31, 2020 Mw6.5 Stanley earthquake: seismotectonics and preliminary aftershock analysis

Lee Liberty

Boise State University

Date & Time
Online-only seminar via Microsoft Teams

I will report on the tectonic framework, seismicity, and monitoring efforts related to the March 31, 2020 Mw 6.5 Stanley, Idaho earthquake. The earthquake sequence has produced both strike-slip and dip-slip motion, and defines the northern limits of the Sawtooth normal fault. This fault separates the Centennial Tectonic Belt, a Basin and Range subprovince, from the Idaho batholith to the west and Challis volcanic belt to the north and east. I will show evidence for a kinematic link between the east-dipping Sawtooth fault and the west-dipping Lost River fault. These opposing faults have recorded four of the five M>=6 Idaho earthquakes from the past 100 years, including 1983 Mw6.9 Borah Peak and the 1944 M6.1 and 1945 M6.0 Seafoam earthquakes. Geological and geophysical data are consistent with fault boundaries, where segmentation may be influenced by preexisting geologic structures. I will show that the limits of both the Sawtooth and Lost River faults extend north beyond their mapped extent, are influenced by the relic Trans-Challis fault system, and that seismicity within this region will likely continue for the coming years. Ongoing seismic monitoring efforts will lead to an improved understanding of ground shaking potential and active fault characteristics.

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