WITHDRAWN Constraining Slab Geometry and Seismic Velocity Structure From Tillamook to Portland, Oregon
Description:
WITHDRAWN Constraints on the location of the megathrust, as well as information about local geologic structure that may impact wave propagation (e.g., seismic wave velocities, sedimentary basins), are important for estimating ground shaking and seismic hazard. In Cascadia, precisely constraining the location of the plate interface and properties of the overriding and subducting crust has remained challenging due to the paucity of local seismicity. This is particularly true for the greater Portland area, where there have been very few attempts to constrain slab geometry and high-resolution seismic velocities at depth. In this study, we use active and passive source data recorded on 192 three-component 5-Hz Fairfield Nodal seismometers in summer 2021 and 2022. The nodes were deployed in an east-west linear array from Tillamook to Portland, Oregon, to better characterize subduction zone structure between the seismogenic zone at depth and population centers at the surface. Teleseismic receiver functions were used to interrogate the depth of the slab interface, while 2-D travel time modeling using recordings of offshore air gun shots from the Cascadia Seismic Imaging Experiment (CASIE21; Carbotte et al., 2024) was used to constrain P-wave velocities and fill a trench-perpendicular gap between the onshore receiver function results and the offshore CASIE21 multichannel seismic reflection images. Results suggest that the depth to the top of the Juan de Fuca plate is ~20 km near the coastline. In addition, we note a potentially thickened subducting crust and change in dip of the slab beneath the western edge of the Coast Range and better constrain the geometry of the western edge of the Siletz terrane. Results also provide new estimates on the depth of the Tualatin Basin near Portland. Overall, this work provides an improved understanding of the local slab geometry and seismic velocity structure beneath northwestern Oregon, which will help improve seismic hazard estimates in the region for future earthquakes.
Session: Earth’s Structure from the Crust to the Core [Poster]
Type: Poster
Date: 4/16/2025
Presentation Time: 08:00 AM (local time)
Presenting Author: Erin
Student Presenter: No
Invited Presentation:
Poster Number: 110
Authors
Erin Wirth Presenting Author Corresponding Author ewirth@usgs.gov U.S. Geological Survey |
Anne Trehu anne.trehu@oregonstate.edu Oregon State University |
Ian Stone istone@usgs.gov U.S. Geological Survey |
Emilie Hooft emilie@uoregon.edu University of Oregon |
Kevin Ward kevin.ward@sdsmt.edu South Dakota School of Mines & Technology |
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WITHDRAWN Constraining Slab Geometry and Seismic Velocity Structure From Tillamook to Portland, Oregon
Category
Earth’s Structure from the Crust to the Core