Tsunami hazard assessment of Canada

The Pacific coastal areas of British Columbia, Washington and Alaska are characterized by a high risk of damaging tsunamis caused by localized underwater landslides. Many of these failure-tsunami events have been documented. While some were related to earthquakes; many others were not. Several failures and tsunamis coincided with extreme low tides and ongoing construction. A three-dimensional numerical model has been developed, based on the theoretical work of Jiang and LeBlond (1994) to describe the relationships between failures and resultant tsunamis occurring in natural basins with complex seafloor morphology. The model has been applied to actual failure sites (e.g., Skagway) and to sites of potential failure (Malaspina Strait, and the Fraser Delta, B.C.).

Geology, 2012

Deepwater landslides are often underestimated as potential tsunami triggers. The North Gorringe avalanche (NGA) is a large (~80 km 3 and 35 km runout) newly discovered and deepwater (2900 m to 5100 m depth) mass failure located at the northern fl ank of Gorringe Bank on the southwest Iberian margin. Steep slopes and pervasive fracturing are suggested as the main preconditioning factors for the NGA, while an earthquake is the most likely trigger mechanism. Near-fi eld tsunami simulations show that a mass failure similar to the NGA could generate a wave >15 m high that would hit the south Portuguese coasts in ~30 min. This suggests that deepwater landslides require more attention in geo-hazard assessment models of southern Europe, as well as, at a global scale, in seismically active margins.

Cascadia subduction zone tsunamis could conceivably cause the loss of tens of thousands of lives on the Pacific Northwest coast of North America. Paleoseismic and other data support Cascadia earthquakes with moment magnitudes of ∼9, rupture lengths of ∼1000 km, and recurrence of 400-600 years; the last event was 301 years ago, so the conditional prob- ability of another occurring in the next 100 years is high. Hydrodynamic simulations depicting destructive potential of Cascadia tsunamis have been hindered chiefly by uncertainties in the earthquake source, rupture simulation methods, and lack of independent verification. Uncer- tainties in the hydrodynamic simulation methods and in oceanographic factors (e.g., non-linear tidal effects) are also of concern; however, coseismic seafloor deformation is a much greater source of error. Research priorities should therefore be directed toward refinement of our knowl- edge of asperities, splay faults, total fault slip, and rupture simulation ...

Geological Society, London, Special Publications

Marine Geology, 2009

... By comparing observations of landslide scarps offshore California to peak seismic acceleration from shake maps and equating a catastrophic failure with a displacement of at least 1 m, Lee et al. (2000) derived a ratio of k y /K PSA ≤ 0.15. ...

2008

To update the tsunami hazard assessment method for Oregon, we (1) evaluate geologically reasonable variability of the earthquake rupture process on the Cascadia megathrust, (2) compare those scenarios to geological and geophysical evidence for plate locking, (3) specify 25 deterministic earthquake sources, and (4) use the resulting vertical coseismic deformations as initial conditions for simulation of Cascadia tsunami inundation at Cannon Beach, Oregon. Because of the Cannon Beach focus, the north-south extent of source scenarios is limited to Neah Bay, Washington to Florence, Oregon. We use the marine paleoseismic record to establish recurrence bins from the 10,000 year event record and select representative coseismic slips from these data. Assumed slips on the megathrust are 8.4 m (290 yrs of convergence), 15.2 m (525 years of convergence), 21.6 m (748 years of convergence), and 37.5 m (1298 years of convergence) which, if the sources were extended to the entire Cascadia margin, give Mw varying from approximately 8.3 to 9.3. Additional parameters explored by these scenarios characterize ruptures with a buried megathrust versus splay faulting, local versus regional slip patches, and seaward skewed versus symmetrical slip distribution. By assigning variable weights to the 25 source scenarios using a logic tree approach, we derived percentile inundation lines that express the confidence level (percentage) that a Cascadia tsunami will NOT exceed the line. Lines of 50, 70, 90, and 99 percent confidence correspond to maximum runup of 8.9, 10.5, 13.2, and 28.4 m (NAVD88). The tsunami source with highest logic tree weight (preferred scenario) involved rupture of a splay fault with 15.2 m slip that produced tsunami inundation near the 70 percent confidence line. Minimum inundation consistent with the inland extent of three Cascadia tsunami sand layers deposited east of Cannon Beach within the last 1000 years suggests a minimum of 15.2 m slip on buried megathrust ruptures. The largest tsunami run-up at the 99 percent isoline was from 37.5 m slip partitioned to a splay fault. This type of extreme event is considered to be very rare, perhaps once in 10,000 years based on offshore paleoseismic evidence, but it can produce waves rivaling the 2004 Indian Ocean tsunami. Cascadia coseismic deformation most similar to the Indian Ocean earthquake produced generally smaller tsunamis than at the Indian Ocean due mostly to the 1 km shallower water depth on the Cascadia margin. Inundation from distant tsunami sources was assessed by simulation of only two Mw 9.2 earthquakes in the Gulf of Alaska, a hypothetical worst-case developed by the Tsunami Pilot Study Working Group (2006) and a historical worst case, the 1964 Prince William Sound Earthquake; maximum runups were, respectively, 12.4 m and 7.5 m.

IntechOpen, 2024

Tsunamis, commonly induced by undersea earthquakes, are formidable natural hazards capable of causing widespread devastation. This comprehensive chapter examines the complex dynamics of tsunamis, their generation mechanisms, and their broad-reaching impacts. The multifaceted nature of tsunami triggers, both seismic and non-seismic, is dissected, highlighting the role of undersea earthquakes, landslides, volcanic eruptions, and meteorological events in driving these devastating natural phenomena. The intricate interplay of seismic parameters such as magnitude, depth, and activity type is elaborated, underscored by an insightful case study on the 2011 Tohoku Earthquake and Tsunami. A pivotal part of the discussion lies in the exploration of non-seismic triggers of tsunamis, an area often overshadowed in tsunami studies. The impact of landslide-induced and volcanically triggered tsunamis is considered alongside the contentious topic of meteorologically influenced tsunami events. Delving further into the genesis of tsunamis, the chapter explores the influences of bathymetry and tectonic structures, particularly in the context of non-seismic tsunami generation. The chapter serves as a beacon for continuous research and predictive modeling in the field of tsunami studies, emphasizing the necessity for societal preparedness and strategic risk mitigation against these potent natural disasters.

Nature Geoscience, 2010