Effects of Willamette Valley Sedimentary Structure on Ground Motions

Accurately estimating ground motions is critical for seismic hazard assessments, particularly in regions like the Cascadia Subduction Zone (CSZ), which has the potential to generate M8-9 megathrust earthquakes. This study focuses on the Willamette Valley (WV), an elongated sedimentary structure extending from Eugene to Portland, Oregon, which has been understudied despite being home to most of Oregon’s population and infrastructure. The WV is characterized by soft, low-density sediments confined between two mountain ranges, the Oregon Coast Range and the Cascade Range, creating significant lateral contrasts in seismic velocity. Using available geologic, geophysical, and structural data, we constructed new velocity models of the WV basin, varying the basin’s depth geometry and seismic velocity structure. To test these models, we performed numerical simulations of three M~4 local crustal earthquakes, and compared our synthetic ground motions with recorded data. Our findings indicate that the sedimentary structure of the WV plays a significant role in amplifying ground motions from local earthquakes. This has important implications for seismic hazard assessments in the region, and highlights the need for a detailed representation of the WV’s shallow structure in regional seismic velocity models. By refining the understanding of the WV’s impact on ground motion, this research contributes to more accurate seismic hazard assessments in the Pacific Northwest, showing the possible regional amplification.

Name thesis:degree_name

M.S.

Level thesis:degree_level

masters

Discipline thesis:degree_discipline

Department of Earth Sciences

Grantor dc:publisher

University of Oregon

Year dc:date.issued

2025

Author dc:creator

• Shimony, Roey

Advisor dc:contributor.advisor

• Sahakian, Valerie

• 3D physics-based Simulations
• Ground Motion
• Seismic Hazard
• Seismology

Statement dc:rights

• All Rights Reserved.

Language dc:language.iso

en_US

Handle dc:identifier.uri

https://hdl.handle.net/1794/30460

OAI record oai:identifier

https://scholarsbank.uoregon.edu/server/oai/request?verb=GetRecord&metadataPrefix=dim&identifier=oai%3Ascholarsbank.uoregon.edu%3A1794%2F30460