Constraining Basin Structure and Characterizing Ground-Motions in the Oregon Willamette Valley
Description:
The Willamette Valley (WV) in Oregon is a sedimentary basin between the Coast Ranges and the Cascades, stretching from Eugene to Portland. Basins often amplify ground motions during earthquakes, increasing seismic hazard, but this region lacks the recordings of medium and large events that allow us to empirically constrain site response due to the shallow geologic, basin structure. Currently, the community standard velocity model of Stephenson et al. (2017) has limited representation of the WV shallow structure. We aim to use existing geologic data and 3D numerical simulations of wave propagation to create a preferred velocity model that is an improvement of the current standard velocity model of this region, with the ultimate goal of constraining likely site response in this populated region.
To this end, we have developed velocity models describing the shallow (<5km) structure of the WV to use in numerical simulations, constrained by oil and gas well logs, geologic and structural maps, seismic profiles and Vs30 values. We made four models, varying the characteristics of the basin’s depth geometry and its sedimentary filling. We then test these models, to determine which best replicates observed waveforms from select recorded small, local crustal earthquakes. We assess performance using residuals between peak amplitudes, shaking durations and arrival times. With our final preferred model, we perform a validation up to 1-2Hz with all available recorded, high-quality waveforms in the region. Ultimately, assuming basin effects are magnitude-independent, we will use our preferred velocity model in a suite of regional numerical simulations of small to moderate (<M5) crustal earthquakes with varying depths and azimuth, to discern average site response in the region due to our shallow crustal structure. Here, we present our preliminary models and validation results for two local, ~M4, earthquakes, recorded throughout the WV. We also show our preferred model, and a comparison of synthetic waveforms from this model, with observed waveforms recorded from four other local crustal earthquakes.
Session: Constraining Seismic Hazard in the Cascadia Subduction Zone [Poster]
Type: Poster
Date: 4/20/2023
Presentation Time: 08:00 AM (local time)
Presenting Author: Roey Shimony
Student Presenter: Yes
Invited Presentation:
Authors
Roey Shimony Presenting Author Corresponding Author rshimony@uoregon.edu University of Oregon |
Valerie Sahakian vjs@uoregon.edu University of Oregon |
Oluwaseun Fadugba ofadugba@uoregon.edu University of Oregon |
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Constraining Basin Structure and Characterizing Ground-Motions in the Oregon Willamette Valley
Category
Constraining Seismic Hazard in the Cascadia Subduction Zone