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Dynamic Rupture Scenarios of the Cascadia Megathrust based on Interseismic Locking Models
  • Yuk Po Bowie Chan,
  • Suli Yao,
  • Hongfeng Yang
Yuk Po Bowie Chan
The Chinese University of Hong Kong
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Suli Yao
Chinese University of Hong Kong
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Hongfeng Yang
The Chinese University of Hong Kong

Corresponding Author:hyang@cuhk.edu.hk

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The Cascadia subduction zone in the Pacific Northwest has well-documented geological records of megathrust earthquakes with the most recent Mw 9 rupture occurring in 1700 A.D. 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. Various interseismic locking models are developed along Cascadia, including offshore uncertainties and different material assumptions. Although they all share similar moment deficits, whether future earthquakes may rupture the entire margin or be segmented, as found in the paleoseismic records, remains unknown. Accordingly, we aim to investigate: (1) possible rupture segmentation patterns, (2) whether south Cascadia can host margin-wide ruptures, and (3) whether the existing locking models suggest similar future rupture scenarios. We estimate the stress distribution constrained by the locking models from static calculation and discover that they lead to different stress distributions, indicating distinct seismic potentials despite their similar moment deficits. 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 hypocenter locations. The extent of Schmalzle-based segmented scenarios matches the proposed historical segmented events, and the margin-wide scenarios are well consistent with the coastal subsidence records of 1700 A.D. Therefore, we propose that three high-slip trench-breaching patches are sufficient for reproducing historical subsidence records. Our reasonable dynamic simulations can be applied in future studies for assessing seismic and tsunami hazards, and also serve as a comparison for non-trench-breaching scenarios.
26 Jan 2023Submitted to ESS Open Archive
01 Feb 2023Published in ESS Open Archive