Natalie Culhane, Masters Candidate
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Natalie Culhane, Masters Candidate
Thesis Proposal:
Immediately south of Mount Hood, OR, the Twin Lakes fault cuts off several drainage channels, forming a series of basins. The fault's relatively sharp topographic expression suggests earthquakes have ruptured at its surface since the region’s last glacial retreat. The presence of basins imply multiple fault ruptures in recent geologic time, deeming it a potential seismic hazard. My thesis investigates sediment from two of the fault-dammed basins, Lower Twin and Frog Lakes. I aim to determine how recently and how frequently the Twin Lakes fault has ruptured since basin formation, filling a gap in the region’s seismic risk analysis.
Work Update:
Over the summer, aided by a team of field assistants and PSU and USGS researchers, I conducted several field campaigns to collect data from Lower Twin and Frog Lakes and along the Twin Lakes fault. We extracted over 30 meters of lake sediment cores from 15 locations across the two lakes by standing atop a platform across two whitewater rafts. At the OSU core lab, I have since scanned all cores for magnetic sensitivity and relative density, and I am currently building a stratigraphic model of the lake sediment. I also collaborated with the geophysical company Norbit to perform active sonar surveys of both lakes, using two strapped paddleboards as a survey boat. Processing this data has resulted in bathymetry maps for both lakes, revealing the deepest part of each lake to be immediately adjacent to the fault scarp. I also performed a paleoseismic trench investigation along a scarp of the Twin Lakes fault between the two lakes. Preliminary interpretations of the terrestrial trench and lake core stratigraphy show colluvial wedges formed by fault ruptures since the region’s last glacial deposits. In the coming months, I will be honing my stratigraphic model of the lake deposits, building an age model for these fault ruptures using radiocarbon ages from collected organics in the sediment, and crafting my findings into a cohesive thesis.
Projected Date of Completion:
I plan to complete my thesis by August 2025.
