Introduction
Due to its location on the
Pacific Ocean "Ring of Fire'" the British Columbia coastline is
vulnerable to tsunamis generated by subduction zone earthquakes,
volcanoes, or submarine landslides (Clague et. al., 2003). The ten
largest earthquakes since 1900 have all been located on the
Pacific Rim, most along the northern margin of the Pacific Plate (Figure 1) (USGS
website).Other
potential tsunami sources
are meteor impacts or explosions, such as the Halifax explosion
of 1917 (Clague et.
al., 2003).
Oceanic
tsunamis can be classified as teletsunamis
or local tsunamis.
Teletsunamis travel long distances across ocean basins, have periods of
an hour or more, and can last for multiple days, while local tsunamis
are generated near the continental shelf, have shorter periods and last
for less time. Teletsunamis cover a larger area of the coastline
than
local tsunamis, thereby posing a greater risk (Clague et. al., 2003). Tsunamis are usually a group of
waves rather than a single wave, and later waves are often larger than
initial waves (Murty, 1977).
Mofjeld et. al. (2000) describe a method
of predicting an envelope for later wave heights from initial tide
guage data, and were able to accurately predict Pacific Ocean tsunami
heights within 1/2 a meter. Choi et. al. (2002) found that the spatial
distribution of tsuna mi
wave heights follows a
log-normal distribution.
Hutchinson
et. al. (2000) studied
sediment cores from Deserted Lake on Vancouver
Island, and estimated that the coast experienced tsunamis generated by
earthquakes in the Cas
cadia subduction zone
approximately 2600, 1600,
and 300 years ago. The
tsunami hazard in British Columbia is greatest for small Vancouver
Island coastal communities such as Tofino, Uclulet, Bamfield and Port
Alberni. Though such communities are small, Tsunami damage resulting from the
1964 Alaska earthquake (magnitude
9.2) was estimated
at 10 million dollars. The
largest wave on the coast
of Vancouver Island during the 1964 event
occurred at the head of Alberni
Inlet,
highlighting the
effect of wave amplification in inlets and other restricted waterways
(Clague et. al., 2003). Blais-Stevens et. al. (1997)
found several potential
seismic/tsunamigenic deposits in the Saanich
inlet, near Victoria,
B.C., dating back 1500 years. This region is close to the subducting
Juan de Fuca plate, and because of it's proximity, tsunami travel times
from an earthquake on this plate boundary
would be short.
Combined with
the devastation to infrastructure and impairment of disaster response
following a large earthquake, a tsunami could potentially arrive
withought warning to this highly populated region. In a GIS study of
human damage resulting from a hypothetical tsunami at Usa town,
Shikoko, Japan, Sugimoto et. al. (2002) predicted that human damage
would be large, as wave flooding would overtake evacuation speeds.
Without incorporating evacuation into their model, the estimates of
death were 10 times higher.
In this project, I model tsunami propagation and
runup (inundation of land) on the B.C. coast, Juan de Fuca Strait and
Gulf Islands,
based on the Alaska earthquake of 1964, as well as a hypothetical
magnitude 9 earthquake at the Juan de Fuca
plate boundary. I examine the different effects of distance and wave
angle on tsunami runup in the strait, and assess the potential for GIS
as a tool for tsunami modelling.