Lacustrine and Terrestrial Paleoseismic Records of the Twin Lakes Fault Near Mt Hood, Oregon, USA
Description:
The Oregon Coast block, located in the Cascadia Subduction Zone forearc, has been translating north and rotating clockwise relative to North America for much of late Cenozoic time. Proposed extension along faults may partially relieve intra-plate strain at the trailing edge of this block. Bare earth lidar topography reveals a series of N- and NNW- trending extensional and oblique faults across the modern High Cascade volcanic arc. Previous paleoseismic investigations have characterized several of these faults as Holocene-active. Immediately south of Mt Hood, the N-S trending, west-dipping Twin Lakes fault impounds a series of small drainages. Scarps up to at least 12 m high and depositional basins on the down-dropped fault block suggest a history of repeated surface-rupturing earthquakes.
In summer 2024, we extracted a series of lake sediment cores from two fault-dammed basins, Frog Lake and Lower Twin Lake. Stratigraphy at Lower Twin includes silt laminae, ash beds, and a wedge of massive coarse sediment that thins away from the subaqueous fault scarp. Preliminary stratigraphic interpretations correlate the coarse wedge to existing post-LGM timing constraints for the penultimate earthquake on the Twin Lakes fault. New multi-beam seismic surveys produce high-resolution bathymetry and sub-bottom profiles of both lakes, revealing a bathymetric low and stratigraphic on-lapping at the Twin Lakes fault scarp. New geologic mapping shows glacial deposits offset at the scarps damming both lakes, with paleo-lacustrine deposits on the uplifted footwall east of Frog Lake. We also excavated a hand-dug paleoseismic trench across a 1.5 m-high, uphill-facing scarp between the two lakes. The trench revealed evidence for a surface-rupturing earthquake that produced 0.7 m vertical offset in glacial deposits across a 2.5 m-wide zone of faults and fissures, capped by an unfaulted ash we interpret as the Old Maid eruptive tephra (1781-1790s C.E.). This new lacustrine and terrestrial evidence suggests the Twin Lakes fault has produced multiple late-Quaternary surface ruptures, designating it a local seismic hazard.
Session: The Landscape Record of Earthquakes and Faulting - I
Type: Oral
Date: 4/16/2025
Presentation Time: 08:45 AM (local time)
Presenting Author: Natalie
Student Presenter: Yes
Invited Presentation:
Poster Number:
Authors
Natalie Culhane Presenting Author nculhane@pdx.edu Portland State University |
Ashley Streig Corresponding Author streig@pdx.edu Portland State University |
Scott Bennett sekbennett@usgs.gov U.S. Geological Survey |
Daniel Gavin dgavin@uoregon.edu University of Oregon |
Johnathan Peterson jvp3@pdx.edu Portland State University |
Amandine Metens amandine@pdx.edu Portland State University |
Kevin Lally kevin.lally@noaa.gov NORBIT |
Cody Henderson cody.henderson@norbit.com NORBIT |
Sandy Schwarzbart sandys@pdx.edu Portland State University |
Benjamin Wagner benwag@pdx.edu Portland State University, Portland, Oregon, United States |
Maureen Murphy maum2@pdx.edu Portland State University, Portland, Oregon, United States |
Lacustrine and Terrestrial Paleoseismic Records of the Twin Lakes Fault Near Mt Hood, Oregon, USA
Session
The Landscape Record of Earthquakes and Faulting