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TitleThe Haida Gwaii tsunami of October 27, 2012
AuthorLeonard, L J; Bednarski, J; Fine, I; Cherniawsky, J; Wright, C
SourceRisky Ground, newsletter of the Centre for natural hazards research, Simon Fraser University 2012, 2012 p. 10-11
LinksOnline - En ligne
Alt SeriesEarth Sciences Sector, Contribution Series 20120365
PublisherSimon Fraser University
File formatpdf
ProvinceBritish Columbia
NTS103B/05; 103B/12
AreaHaida Gwaii
Lat/Long WENS-132.0000 -131.5000 52.7500 52.2500
Subjectsgeophysics; tsunami; earthquakes; earthquake mechanisms; geological hazards
Illustrationslocation maps; photographs
ProgramPublic Safety Geoscience, Reducing Risk Program Management
AbstractThe October 27 magnitude 7.7 Haida Gwaii earthquake involved a predominantly thrust faulting mechanism beneath the seafloor off western Moresby Island, BC. Such an event is expected to produce locally significant tsunami waves, with runup in excess of 3 m on the unpopulated west coast of Moresby Island. Elsewhere, smaller waves are expected and were observed. Tsunami waves as small as 1.5 m in amplitude can cause damage, and those exceeding 3 m would be extremely destructive on populated coastlines. A team was deployed to Haida Gwaii in mid-November in order to (1) confirm that substantial tsunami waves impacted the west coast of Moresby Island, given the absence of witnesses and local tide gauges; (2) collect data to provide critical ground-truthing for modelling of the earthquake rupture and tsunami generation. Three helicopter survey flights were undertaken along the west coast of Moresby Island, with landings for more detailed observations at six inlets and coves. The team found evidence for significant tsunami runup (up to at least 4-5 m above the tide level at the time) at the heads of inlets from Blue Heron Bay in the north to Gowgaia Bay in the south. Evidence for tsunami runup includes plastic (e.g., bottles and sheeting), Styrofoam, fishing floats, seaweed, dead fish, driftwood logs and other debris present in and alongside creek beds as well as on the forest floor and draped over fallen trees, up to tens of metres from the shore. Pieces of seaweed in tree branches indicate minimum flow depths of up to 2.2 m above the ground. Log movements indicate a variety of flow directions (landward, shoreward and oblique).
The 2012 Haida Gwaii tsunami is the largest locally-generated earthquake tsunami documented in written historical time (the last ~150 years) on the Pacific coast of Canada. There were no witnesses to the significant tsunami waves, and a lack of infrastructure to sustain damage, but a similar tsunami occurring in the summer would put the lives of kayakers, boaters and campers in these inlets at risk. The tsunami data will help to advance understanding of earthquake rupture and tsunami generation not only for the Haida Gwaii region, but also for similar potential events off northern Vancouver Island, and for much larger future events on the Cascadia subduction zone, which will have a massive impact on populated regions throughout coastal BC.

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