Collaborative Research: Estimating shallow shear-wave velocity in basins throughout the Pacific Northwest: an imperative for accurate ground motion prediction

Large earthquakes can cause devastating damage, particularly in regions where soft sediments amplify shaking. Many major cities around the world, including those in the Pacific Northwest of the United States, are built on sedimentary basins that can trap seismic waves and greatly increase both their intensity and duration of shaking. Over 12 million people live in this region, which has the potential to produce both a megathrust great earthquake (potentially M9+) and also smaller crustal earthquakes that occur closer to population centers. This project aims to improve our understanding of how local geological structures affect earthquake ground motion amplification in the Pacific Northwest, particularly in densely populated sedimentary basins. The researchers will develop new ways to constrain the subsurface structure of Cascadia forearc basins to provide better information that can guide estimates of ground motions from seismic hazards. All data, methods, and results will be openly shared to support the broader scientific community and regional velocity model-building efforts, including collaboration with the Cascadia Region Earthquake Science Center (CRESCENT). This study will develop and apply two complementary passive seismic techniques to characterize the shallow subsurface structure of the Cascadia forearc basin, where most of the population in the Pacific Northwest lives. The research team will use particle motion analysis from teleseismic earthquakes to help define shallow shear-wave velocity structure inside and outside the basin. Then, using horizontal-to-vertical spectral ratios from local earthquakes and ambient noise, basin geometry will be constrained. The results will be incorporated into regional-scale seismic velocity models such as the Cascadia Region Earthquake Science Center (CRESCENT) Community Velocity Model (CVM). Numerical simulations will help assess how the newly defined basin structures amplify ground motion during earthquakes. This research addresses a key gap in understanding how local geology influences seismic hazard at a regional scale—an issue of critical importance for earthquake-prone areas globally. The methods developed here are globally applicable and will represent a new approach to determining seismic shaking potential in basin settings. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.