The 1983 Borah Peak earthquake (M7.3) (Idaho - USA) - 3D architecture and seismotectonics along the Lost River fault from field observations and high-resolution topography integrated with seismological data

Simone Bello, Ramon Arrowsmith, Chelsea Scott, Giusy Lavecchia, Tyler Scott, Rita De Nardis, & Federica Ferrarini

Submitted August 11, 2019, SCEC Contribution #9418, 2019 SCEC Annual Meeting Poster #125

The Lost River Fault (LRF; northern Basin and Range, USA) is composed of six segments and of a large number of multi-scale en-echelon SW- to SSW dipping normal and normal oblique fault surfaces. Two NNW-SSE trending segments, known as Warm Spring (WSS) and Thousand Springs (TSS), failed in the 1983 Borah Peak earthquake (ML7.3), the largest historic event in Idaho and one of the largest in the Basin and Range. Consistent with focal mechanisms of the mainshock, field observations show a normal-sinistral sense of motion along a southwest dipping plane (Crone and Machette, 1984).

The 120 km long fault trace lends itself well to the study of the segmentation patterns. After 35 years, spectacular co-seismic fault scarps with vertical displacement up to ~2.7 meters are still well preserved for a length of ~37 km. Structural field work was carried out along the entire Lost River Fault in spring 2019 mapping fault traces and characterized fault zone lithologies. Along the 1983 earthquake epicentral area, we examined the surface ruptures. Long-term and coseismic fault/slip data were acquired using FieldMove on an iPad for digital field mapping.

UAV overflights produced high resolution imaging to construct topographic and orthophoto maps and 3D models. These allowed us to define the surface fault trace geometry, to highlight complex coseismic rupture patterns along TSS and WSS, and to systematically extrapolate the height of the fault scarps, generating profiles of throw along strike. Further analysis of the high-resolution images indicates piercing points that will be used as displacement vectors for paleostress analysis.

The high-resolution data and the multidisciplinary approach adopted for the Borah Peak earthquake surface faulting, will allow a comparison with other similar intra-continental earthquakes (Irpinia 1980 and Central Italy 2016-2017 seismic sequences), opening new horizons of international and inter-university collaborations and projects.

Key Words
Borah Peak earthquake, seismotectonics, high-resolution data

Citation
Bello, S., Arrowsmith, R., Scott, C., Lavecchia, G., Scott, T., De Nardis, R., & Ferrarini, F. (2019, 08). The 1983 Borah Peak earthquake (M7.3) (Idaho - USA) - 3D architecture and seismotectonics along the Lost River fault from field observations and high-resolution topography integrated with seismological data . Poster Presentation at 2019 SCEC Annual Meeting.


Related Projects & Working Groups
Earthquake Geology