Defining megathrust tsunami source scenarios for northernmost Cascadia

Dawei Gao, Kelin Wang (), Tania L. Insua, Matthew Sypus, Michael Riedel and Tianhaozhe Sun
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Dawei Gao: University of Victoria
Kelin Wang: University of Victoria
Tania L. Insua: University of Victoria
Matthew Sypus: University of Victoria
Michael Riedel: GEOMAR Helmholtz Centre for Ocean Research
Tianhaozhe Sun: Pennsylvania State University

Natural Hazards: Journal of the International Society for the Prevention and Mitigation of Natural Hazards, 2018, vol. 94, issue 1, No 24, 445-469

Abstract: Abstract For assessing tsunami hazard in northernmost Cascadia, there is an urgent need to define tsunami sources due to megathrust rupture. Even though the knowledge of Cascadia fault structure and rupture behaviour is limited at present, geologically and mechanically plausible scenarios can still be designed. In this work, we use three-dimensional dislocation modelling to construct three types of rupture scenarios and illustrate their effects on tsunami generation and propagation. The first type, buried rupture, is a classical model based on the assumption of coseismic strengthening of the shallowest part of the fault. In the second type, splay-faulting rupture, fault slip is diverted to a main splay fault, enhancing seafloor uplift. Although the presence or absence of such a main splay fault is not yet confirmed by structural observations, this scenario cannot be excluded from hazard assessment. In the third type, trench-breaching rupture, slip extends to the deformation front and breaks the seafloor by activating a frontal thrust. The model frontal thrust, based on information extracted from multichannel seismic data, is hypothetically continuous along strike. Our low-resolution tsunami simulation indicates that, compared to the buried rupture, coastal wave surface elevation generated by the splay-faulting rupture is generally 50–100% higher, but that by trench-breaching rupture is slightly lower, especially if slip of the frontal thrust is large (e.g. 100% of peak slip). Wave elevation in the trench-breaching scenario depends on a trade-off between enhanced short-wavelength seafloor uplift over the frontal thrust and reduced uplift over a broader area farther landward.

Keywords: Tsunami sources; Cascadia subduction zone; Megathrust earthquakes; Splay-faulting rupture; Trench-breaching rupture; Dislocation modelling (search for similar items in EconPapers)
Date: 2018
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DOI: 10.1007/s11069-018-3397-6

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