Impact of Hypocenter Location on Rupture Extent and Ground Motion: A Case Study of Southern Cascadia

Abstract

AbstractThe Cascadia subduction zone has well‐documented geological records of megathrust earthquakes with the latest ∼Mw 9 rupture occurring in CE 1700. The paleoseismic observations suggest that southern Cascadia is mature for future earthquakes since the last event. Consequently, it is crucial to investigate the potential rupture scenarios. Although existing interseismic locking models share similar moment deficits, whether future earthquakes would be margin‐wide or segmented, as suggested by paleoseismic records, remains unknown. Accordingly, we aim to investigate: (a) possible rupture segmentation patterns, (b) whether south Cascadia can host margin‐wide ruptures, and (c) whether the existing locking models suggest similar future rupture scenarios. Assuming constant effective normal stress, we estimate the stress distribution constrained by the locking models (i.e., Gamma model from Schmalzle et al. (2014, https://doi.org/10.1002/2013GC005172), the preferred model from S. Li et al. (2018, https://doi.org/10.1029/2018JB015620), and the best‐fit model from Lindsey et al. (2021, https://doi.org/10.1038/s41561-021-00736-x)) from static calculation and discover they lead to different stress distributions, indicating distinct seismic potentials. Our dynamic rupture scenarios show that the south can generate both segmented ruptures (>Mw 7.3–8.4) and margin‐wide ruptures (>Mw 8.6) depending on the hypocenter location. The along‐strike rupture length appears to coincide with rupture lengths hypothesized from paleoseismology, and the Schmalzle model produces reasonable coastal subsidence amplitudes from the CE 1700 event. Therefore, we propose that three high‐slip trench‐breaching patches are sufficient for reproducing historical subsidence records. Our results can be further applied in seismic and tsunami hazard assessment, and serve as a comparison for non‐trench‐breaching scenarios.