Rupture Process of the M 6.5 Stanley, Idaho, Earthquake Inferred from Seismic Waveform and Geodetic Data

The 2020 M 6.5 Stanley, Idaho, earthquake produced rupture in the north of the active Sawtooth fault in the northern basin and range at depth, without any observable sur-face rupture. Global Positioning System (GPS) and Interferometric Synthetic Aperture Radar (InSAR) data yield several millimeters of static offsets out to -100 km from the rupture and up to -0:1 m of near-field crustal deformation. We combine the GPS and InSAR data with long-period regional seismic waveforms to derive models of kinematic slip and afterslip. We find that the coseismic rupture is complex, likely involving up to 2 m combined left-lateral strike slip and normal slip on a previously unidentified -south-southeast-striking fault. This slip is predominantly left-lateral strike slip, different from the dominant east-northeast?west-northwest normal faulting of the region. At least one -northeast-trending fault, likely associated with the Trans-Challis fault system, is inferred to have accommodated a few decimeters of right-lateral afterslip, consistent with vigorous aftershock activity at depth along northeast-trend-ing lineations.

Automated summary

The 2020 M 6.5 Stanley, Idaho, earthquake resulted in deep ruptures in the northern part of the Sawtooth fault without any visible surface rupture. Analysis of GPS and InSAR data, combined with models derived from regional seismic waveforms, revealed a complex coseismic rupture involving left-lateral strike slip and normal slip on a previously unidentified fault. The aftershock activity along northeast-trending lineations suggests additional right-lateral afterslip along a fault likely associated with the Trans-Challis fault system.