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TitleDefining megathrust tsunami source scenarios for northernmost Cascadia
AuthorGao, D; Wang, KORCID logo; Insua, T L; Sypus, M; Riedel, M; Sun, TORCID logo
SourceNatural Hazards 2018 p. 1-25,
Alt SeriesNatural Resources Canada, Contribution Series 20180073
PublisherSpringer Nature
Mediapaper; on-line; digital
File formatpdf; html
ProvinceBritish Columbia; Western offshore region
NTS92B; 92C; 92D; 92E; 92F; 92G; 92K; 92L
AreaVancouver Island; Pacific Ocean; Washington State; Oregon; Canada; United States of America
Lat/Long WENS-129.0000 -122.0000 51.0000 46.0000
Subjectsgeophysics; tectonics; marine geology; structural geology; earthquakes; tsunami; source areas; crustal movements; crustal uplift; modelling; bedrock geology; structural features; faults; deformation; seismic data; seismic interpretations; computer simulations; wave propagation; structural analyses; structural controls; Cascadia Subduction Zone; Nootka Fault Zone; Explorer Plate; North American Plate; Pacific Plate
Illustrationsschematic models; geoscientific sketch maps; 3-D models; tables; profiles; seismic profiles
ProgramPublic Safety Geoscience Assessing Earthquake Geohazards
Released2018 07 02
AbstractFor 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.
Summary(Plain Language Summary, not published)
In tsunami hazard analysis, the first step is to define source characteristics. In this work, we construct megathrust source scenarios for northernmost Cascadia off SW British Columbia and demonstrate how the sources generate tsunami waves. In addition to the buried rupture and splay faulting scenarios that had been previously considered for tsunami hazard assessment in Oregon, we have included trench-breaching scenarios based on lessons learned from the M9 2011 Tohoku-oki earthquake. The results form the basis for more detailed and systematic analysis of tsunami hazard in SW BC due to a Cascadia megathrust event.

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