Observations of the 2011 Tohoku Tsunami on the Coast of British Columbia

Abstract:

The Great Tohoku Earthquake (M_w 9.0) of 11 March 2011 generated highly catastrophic tsunami waves that reached runup heights of up to 40 m along the coast of Japan and were recorded by numerous coastal tide gauges and bottom pressure stations throughout the Pacific Ocean. Near the coast of British Columbia (BC), the tsunami was measured by 15 permanent tide gauges, including gauges located well inside the Strait of Georgia and at Patricia Bay in Saanich Inlet (the site of the Institute of Ocean Sciences, IOS). Tsunami waves were also recorded by 5 temporary tide gauges within Victoria Harbour waterways (Gorge and Portage inlets), by 4 NEPTUNE-Canada bottom cable observatories on the Vancouver Island shelf and by 3 VENUS bottom pressure recorders within Saanich Inlet. Maximum tsunami wave heights observed on the outer BC coast were 1.0-1.5 m, while those within the sheltered basins of the inner coast were about ten times lower. The tsunami wave signal was also observed in the temperature, salinity and current velocity records of CTDs and an ADCP installed in an anoxic Canadian fjord on the coast of Vancouver Island. The collected data enabled us to examine the statistical and spectral properties of the 2011 Tohoku tsunami on the coast of British Columbia and to estimate the relative tsunami risk for this coast from distant earthquakes. The tsunami record from the deepest NEPTUNE (CORK) station was used as the input function for the IOS regional tsunami forecast model. The computed and observed tsunami wave forms for this event were in good agreement.