First Advisor
Adam Booth
Date of Award
Spring 6-14-2026
Document Type
Thesis
Degree Name
Bachelor of Science (B.S.) in Geology and University Honors
Department
Geology
Language
English
Subjects
Gales Creek Fault, Landslides, Surface roughness, Earthquakes, Co-seismic, LiDAR
Abstract
Modern coseismic landslides cluster near the surface trace of the fault that ruptured, suggesting that clustering of paleolandslides may record information about paleoearthquakes. This study documents the pattern of prehistoric landslides near the Gales Creek Fault (GCF), northwest Oregon, to assess whether it reflects an independently known paleoearthquake. The GCF is located northwest of Portland through the Cascadia fore-arc basin where landslides are often triggered by intense rainfall during the wet season or potentially by seismic shaking on the megathrust or on crustal faults. In order to understand how a seismic event on the GCF will impact landslide distribution I isolated plausible earthquake-triggered landslides that correspond to the most recent known earthquake, 853-1168 years ago, and analyzed them independently. This was done by creating a landslide inventory map and analyzing surface roughness. Surface roughness was used as a proxy for age and only deposits with an average roughness value that corresponded to the age of the last earthquake were used. Once the plausible coseismic landslides were isolated I investigated how they were distributed with respect to fault proximity. In sedimentary bedrock, landslide density was dominated by a cluster of large landslide complexes that were located about 15 km NE of the fault. The lack of clustering near the fault trace suggests that factors other than earthquakes are more important for triggering landslides in sedimentary units. In volcanic bedrock, landslide density decreased with distance from the fault. These findings imply that basalt may be more susceptible to earthquake triggered landslides. The outcomes of this study therefore help us understand how a future earthquake on the GCF could influence landslide distribution and to develop a framework for considering fault proximity in hazard zoning.
Recommended Citation
Rheingans, Jacqueline R., "Assessing Spatial Distribution of Plausible Earthquake-Triggered Landslides Relative to ca. 1000 ybp Earthquake on the Gales Creek Fault" (2026). University Honors Theses. Paper 1902.