Incorporating the M9 Project Simulations Into Non-Ergodic Site and Path Terms for the Cascadia Region Outside the Seattle Region
Description:
Sung and Abrahamson (2022) incorporated the simulations for the Seattle region from the M9 Project (Frankel et al., 2018) into the Abrahamson and Gulerce (2020) (AG20) ground-motion model (GMM), resulting in a partially non-ergodic GMM that captured the long-period site-specific combined site and path effects due to the 3-D crustal model for large-magnitude Cascadia interface earthquakes. The M9 Project also simulated the ground motions for the larger Cascadia region but with sparser spatial sampling of 20 km x 20 km. We use these simulation results to develop the non-ergodic site and path effects for the larger Cascadia region. The average basin-depth (Z2.5) scaling for the larger region has weaker basin effects than for the Seattle region. As a result, extrapolating the Seattle-region non-ergodic GMM outside the Seattle region does not work well for shallow basin sites. The non-ergodic terms for the larger Cascadia region span a smaller range than for the Seattle region. Overall, the non-ergodic aleatory variability for the non-ergodic GMM outside the Seattle region was reduced by 15% compared to the global aleatory variability of the AG20 model. This is similar to the reduction for the global single-station sigma, indicating that the path effects from the 3-D crustal structure are not strong outside the Seattle region. In addition, sites located close to the coastline at rupture distances less than 40 km show a significant increase in both the median and the aleatory variability compared to sites at distances larger than 50 km. This increase in the standard deviation is likely related to the variability of the distances to the main subevents in M9 earthquakes for the same rupture distance. The ergodic and non-ergodic hazards are compared for a suite of site locations. For example, using the non-ergodic GMM for the Portland region, the T=3 sec spectral acceleration with a 10,000-yr return period is a factor of 1.16 larger than the results for the ergodic GMM.
Session: USGS National Seismic Hazard Models: 2023 and Beyond
Type: Oral
Date: 4/18/2023
Presentation Time: 10:15 AM (local time)
Presenting Author: Chih Hsuan Sung
Student Presenter: No
Invited Presentation:
Authors
Chih Hsuan Sung Presenting Author Corresponding Author karensung@berkeley.edu University of California, Berkeley |
Norman Abrahamson abrahamson@berkeley.edu University of California, Berkeley |
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Incorporating the M9 Project Simulations Into Non-Ergodic Site and Path Terms for the Cascadia Region Outside the Seattle Region
Category
USGS National Seismic Hazard Models: 2023 and Beyond