Empirical Assessment of Site and Basin Response in the Pacific Northwest via Testing Site-Response Models for Different Tectonic Regimes

Sean K. Ahdi, Brad T. Aagaard, Morgan P. Moschetti, Oliver S. Boyd, Grace A. Parker, & William J. Stephenson

Published September 10, 2023, SCEC Contribution #13238, 2023 SCEC Annual Meeting Poster #190 (PDF)

We test the hypothesis that site-response models are independent of earthquake source parameters by analyzing ground-motion records in the Portland, Oregon, region. We assess whether empirical site-response models developed for subduction-zone ground-motion models (GMMs), regionalized for the Pacific Northwest (PNW), perform as well as the site-response model developed for crustal earthquakes in California. This study builds upon our previous regional empirical analyses of basin response for the California Great Valley, the Reno-Sparks basins in Nevada, and the Portland-Tualatin basins in Oregon. Those analyses showed that the Boore et al. (2014) and Campbell and Bozorgnia (2014) NGA-West2 GMMs improved predictions of basin response in the California Great Valley but did not perform as well in the shallow Reno-Sparks basins or the more geologically complex Portland-Tualatin basins.

We first analyze basin response by compiling and processing regional ground-motion data and performing residuals analyses and mixed-effects regressions. We build upon the study in Portland by (1) improving VS30 characterization of stations that recorded ground motions by using measured VS30 values where available or alternative proxy-based VS30 prediction models other than topographic slope and (2) computing GMM estimates with both an NGA-Subduction empirical site-response model for the PNW and the site-response model built into the NGA-West2 GMMs for shallow crustal events. If the site-response models are shown to be independent of earthquake source type, we can reduce uncertainty in ground-motion predictions by replacing site-response models in ergodic GMMs with region-specific site-response models developed using a subset of potential earthquake sources. This would result in improved ground-motion estimation in regions within national-scale seismic hazard studies that generally employ global ergodic site-response models at all locations within a tectonic regime.

Key Words
site response, ground motion models, shallow crustal, subduction zones

Citation
Ahdi, S. K., Aagaard, B. T., Moschetti, M. P., Boyd, O. S., Parker, G. A., & Stephenson, W. J. (2023, 09). Empirical Assessment of Site and Basin Response in the Pacific Northwest via Testing Site-Response Models for Different Tectonic Regimes. Poster Presentation at 2023 SCEC Annual Meeting.

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