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TitleField survey following the 28 October 2012 Haida Gwaii tsunami
AuthorLeonard, L J; Bednarski, J M
SourcePure and Applied Geophysics 2014, 16 pages, https://doi.org/10.1007/s00024-014-0792-0
Year2014
Alt SeriesEarth Sciences Sector, Contribution Series 20130462
Documentserial
Lang.English
Mediaon-line; digital
File formatpdf
ProvinceBritish Columbia; Western offshore region
NTS103B; 103C; 103F; 103G
AreaHaida Gwaii; Graham Island; Moresby Island
Lat/Long WENS-134.0000 -132.0000 54.0000 52.0000
Subjectsmarine geology; geophysics; tsunami; earthquakes; faults, thrust
ProgramAssessing Earthquake Geohazards, Public Safety Geoscience
AbstractThis article documents the near-field effects of the largest tsunami of 2012 (globally), which occurred following Canada's second-largest recorded earthquake, on a thrust fault offshore western Haida Gwaii on October 28 (UTC). Despite a lack of reported damaging waves on the coast of British Columbia (largest amplitudes were recorded in Hawaii), three field surveys in the following weeks and months reveal that much of the remote unpopulated, uninstrumented coastline of western Haida Gwaii was impacted by significant tsunami waves that reached up to 13 m above the state of tide. Runup exceeded 3 m at sites spanning ~200 km of the coastline. Greatest impacts were apparent at the heads of narrow inlets and bays on western Moresby Island, where natural and manmade debris with a clear oceanward origin was found on the forest floor and caught in tree branches, inferring flow depths up to 2.5 m. Bays that see regular exposure to storm waves were generally less affected; at these sites a storm origin cannot be ruled out for the debris surveyed. Logs disturbed from their apparent former footprints on the forest floor at the head of Pocket Inlet provide evidence of complex runup, backwash and oblique flow patterns, as noted in other tsunamis. Discontinuous muddy sediments were found at a few sites; sedimentation was not proportional to runup. Lessons learned from our study of the impacts of the Haida Gwaii tsunami may prove useful to future post-tsunami and paleotsunami surveys as well as tsunami hazard assessments.
Summary(Plain Language Summary, not published)
This article documents the effects of the largest tsunami of 2012 (globally), which occurred following Canada's second-largest recorded earthquake, on a thrust fault offshore western Haida Gwaii on October 28 (UTC). Field surveys reveal that the remote unpopulated west coast of Haida Gwaii was impacted by significant tsunami waves that reached up to 13 m above the tide level at the time. Waves reaching more than 3 m above tide level affected ~200 km of the coastline. Greatest impacts were apparent at the heads of narrow inlets and bays on western Moresby Island, where debris including plastic bottles and fishing floats, driftwood, and seaweed was found on the forest floor and caught in tree branches up to 2.5 m above the ground. Lessons learned from this study of the impacts of the Haida Gwaii tsunami are applicable for studies of past and future tsunamis, and will contribute to a better understanding of tsunami hazard along the Pacific coast of Canada and similar settings worldwide.
GEOSCAN ID293666