60-41 A 175-Year Record of Vertical Land Motion in the Coos Bay, Oregon Area From Repeated Leveling and Tide Gauge Records: Characterizing Cascadia Strain and Sea Level Rise​

Session: 2YC and 4YCU Geoscience Student Research Poster Showcase

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Subduction zone earthquakes are a major geologic hazard that impact the American West Coast. These quakes originate from an area known as the Cascadia Subduction Zone, or CSZ. In the CSZ, the denser oceanic Juan de Fuca Plate is subducting beneath the less dense continental North American Plate. This movement causes strain to build up in the CSZ as the coast uplifts, which will be released during a subsequent megathrust quake. 

The last major subduction zone earthquake that impacted the Oregon Coast occurred in 1700; it is difficult to know exactly when another such earthquake will happen. Our study aims to provide a timeline of strain buildup starting relatively soon after the 1700 earthquake, which can offer valuable insight into how the CSZ behaves. Our research primarily focuses on gaining a deeper understanding of how strain has accumulated along the Oregon Coast over the past 175 years in the form of vertical land motion, with the goal of better defining the seismic hazard faced by millions of people in the Pacific Northwest.

To characterize coastal uplift in this area, we have utilized both sea level data, collected with tidal gauges, and land leveling data, collected with first- and second-order surveying, over the past 175 years in the Coos Bay, OR, area. As survey elevation data is based on mean sea level, we compared these data points to develop a more accurate model for true uplift rate and subduction zone strain along the Cascadia Subduction Zone in this region. We hope to continue to build on this data by deploying a tidal gauge near Empire Dock in Coos Bay to collect water level, temperature, and salinity data, and we plan to conduct small-scale land leveling on the coast to tie our new data points together.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-9556

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