Inferring paleoearthquake characteristics from landslides and geomorphology: Gales Creek Fault, Oregon

The geomorphic record contains important, but imperfect, evidence of paleoearthquake characterstics that can supplement traditional paleoseismic investigations. Here, we isolated a sample of plausibly coseismic paleolandslides to infer the rupture extent of an independently identified paleoearthquake on the Gales Creek Fault ~1000 years ago and to identify additional possible paleoearthqukes. Plausibly coseismic landslides were identified by combining two geomorphic constraints: quantifying average deposit surface roughness from lidar as a proxy for age, and applying an Index of Potential Trigger (IPT) metric to distinguish likely coseismic from likely rainfall-triggered landslides. Results imply that landslide distributions may identify paleoearthquakes that are not always identifiable in paleoseismic trenches.