Characteristics and Extent of the North Olympic Fault Zone, Clallam County, Washington
Research Mentor(s)
Colin Amos and Liz Schermer
Description
In the Cascadia subduction zone of Washington state, upper plate contraction manifests as conjugate strike-slip faults flanking the northern and southern margins of the Olympic Mountains. The northern bounding fault, the North Olympic Fault Zone (NOFZ), strikes roughly west-northwest, parallel to the Strait of Juan de Fuca, and exhibits a post-glacial dextral slip rate of 2 mm/yr. Surficial geological mapping based on new airborne lidar data demonstrates that the fault zone extends an additional 30 km along strike to the west, indicating potential earthquake rupture lengths up to ~90 km. Here, we use field and lidar data to map and describe fault scarps along the western NOFZ to evaluate structural and earthquake connectivity with the eastern NOFZ. Scarps in the study area displace Quaternary glacial and post-glacial fluvial deposits although much of the fault trace is buried by surficial deposits or expressed solely in bedrock. Preliminary field and lidar analyses reveal that dextral geomorphic offsets of post-glacial incised channels range up to ~30 m with most values between 10-15 m. Initial analysis of vertical separation data reveal an average ~8 m with most values between 1-5 m. These analyses suggest that the post-glacial faulting is predominately dextral, similar to kinematics observed further east on the NOFZ. While we find that the strike and general kinematics of the western scarps are consistent with the eastern NOFZ scarps, the western scarps described here are significantly more segmented and discontinuous. Extending the NOFZ rupture length has the potential to increase theoretical moment magnitudes from a full-fault rupture from Mw 7.1-7.3 to Mw 7.5. New luminescence ages from samples of glacial and post-glacial surfaces cut by the fault will constrain slip rates and help us further relate the western scarps to the eastern NOFZ.
Document Type
Event
Start Date
May 2022
End Date
May 2022
Location
SMATE Library (Bellingham, Wash.)
Department
Geology
Genre/Form
student projects; posters
Type
Image
Rights
Copying of this document in whole or in part is allowable only for scholarly purposes. It is understood, however, that any copying or publication of this document for commercial purposes, or for financial gain, shall not be allowed without the author’s written permission.
Language
English
Format
application/pdf
Characteristics and Extent of the North Olympic Fault Zone, Clallam County, Washington
SMATE Library (Bellingham, Wash.)
In the Cascadia subduction zone of Washington state, upper plate contraction manifests as conjugate strike-slip faults flanking the northern and southern margins of the Olympic Mountains. The northern bounding fault, the North Olympic Fault Zone (NOFZ), strikes roughly west-northwest, parallel to the Strait of Juan de Fuca, and exhibits a post-glacial dextral slip rate of 2 mm/yr. Surficial geological mapping based on new airborne lidar data demonstrates that the fault zone extends an additional 30 km along strike to the west, indicating potential earthquake rupture lengths up to ~90 km. Here, we use field and lidar data to map and describe fault scarps along the western NOFZ to evaluate structural and earthquake connectivity with the eastern NOFZ. Scarps in the study area displace Quaternary glacial and post-glacial fluvial deposits although much of the fault trace is buried by surficial deposits or expressed solely in bedrock. Preliminary field and lidar analyses reveal that dextral geomorphic offsets of post-glacial incised channels range up to ~30 m with most values between 10-15 m. Initial analysis of vertical separation data reveal an average ~8 m with most values between 1-5 m. These analyses suggest that the post-glacial faulting is predominately dextral, similar to kinematics observed further east on the NOFZ. While we find that the strike and general kinematics of the western scarps are consistent with the eastern NOFZ scarps, the western scarps described here are significantly more segmented and discontinuous. Extending the NOFZ rupture length has the potential to increase theoretical moment magnitudes from a full-fault rupture from Mw 7.1-7.3 to Mw 7.5. New luminescence ages from samples of glacial and post-glacial surfaces cut by the fault will constrain slip rates and help us further relate the western scarps to the eastern NOFZ.
