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Presentation Type

Oral Presentation

Subjects

Paleoseismology -- Oregon -- Strawberry Mountains, Faults (Geology) -- Oregon, Paleoseismology -- Holocene

Department

Geology

Advisor

Ashley Streig

Student Level

Masters

Abstract

New high-resolution lidar data for the Strawberry Mountains, Oregon has revealed youthful fault scarps that likely result from Holocene-age earthquakes. Scarps have been mapped running roughly east-west in the north foothills of the Strawberry Mountains through National Forest and Wilderness land, as well as another scarp lineament running south along the uppermost John Day River to Summit Prairie. The proposed research will evaluate the timing and size of displacements along the faults as well as how the faults relate to regional tectonic stresses. The Strawberry Mountains contained numerous alpine glaciers in the Last Glacial Maximum (LGM), and glacial moraines are offset 1 – 1.5 m by the faults. The age of moraines can be estimated using cosmogenic exposure dating and with measured offsets, a slip rate can be determined. Organics (charcoal) collected from within scarp-derived colluvium can be dated with 14C to constrain the age of the most recent earthquake. Measured fault scarp displacements will be used with empirical scaling relationships to estimate paleo-earthquake magnitudes.

Persistent Identifier

https://archives.pdx.edu/ds/psu/35446

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Evaluating Active Faults and Earthquakes in the Strawberry Mountains, Oregon

New high-resolution lidar data for the Strawberry Mountains, Oregon has revealed youthful fault scarps that likely result from Holocene-age earthquakes. Scarps have been mapped running roughly east-west in the north foothills of the Strawberry Mountains through National Forest and Wilderness land, as well as another scarp lineament running south along the uppermost John Day River to Summit Prairie. The proposed research will evaluate the timing and size of displacements along the faults as well as how the faults relate to regional tectonic stresses. The Strawberry Mountains contained numerous alpine glaciers in the Last Glacial Maximum (LGM), and glacial moraines are offset 1 – 1.5 m by the faults. The age of moraines can be estimated using cosmogenic exposure dating and with measured offsets, a slip rate can be determined. Organics (charcoal) collected from within scarp-derived colluvium can be dated with 14C to constrain the age of the most recent earthquake. Measured fault scarp displacements will be used with empirical scaling relationships to estimate paleo-earthquake magnitudes.