Geoscience Reference
In-Depth Information
Fig. 10.9
Ryoishi, a typical
town along the Sanriku coast of
Japan protected against tsunami
by a 6 m high wall built in 1973.
These walls are now common
around the Japanese coast;
however, they do not offer
protection against tsunami having
historical run-ups. Source
Fukuchi and Mitsuhashi (
1983
)
Fig. 10.10
The T¯hoku
Tsunami March 11, 2011
overtopping the wall at Ryoishi
even though it had been extended
in 1985 to a height of 9.5 m—see
Fig.
10.9
for initial wall. Forty
people died here during the 2011
event. Source Ryuji Miyamoto.
Copyright Hashime Seto
a building, it was impossible to escape. If they survived, they
were then stranded until rescued days later. Those that
decided to flee by car found themselves caught in traffic jams,
blocked by accidents, simply disorientated by the chaos,
caught up in the wave, or in some cases deposited on top of
the three-story buildings where some residents had sought
refuge (Fig.
10.11
). Foolishly, some people took the initial
warning as a sign to retrieve possessions or relatives from
danger and headed back into threatened areas. In the end, the
safest strategy was to flee on foot—and not drive—to the
hills. The death toll from this disaster was so high simply
because the tsunami culture nationally, regionally, and
locally was inadequate given the magnitude of the tsunami.
All of the warning systems in the Pacific assume that a
teleseismic tsunami originates in some under populated
country
many places, evacuation from tsunami is difficult even
with adequate warning because sea cliffs back numerous
earthquakes here have tended to occur every 30-50 years
with a deadly impact. Chile does not have the privilege of
being able to rely upon the Pacific Tsunami Warning
System, because what is a distant earthquake to the PTWS
can well be a localized earthquake in Chile. Project
THRUST (Tsunami Hazards Reduction Utilizing Systems
Technology) was established offshore from Valparaiso,
Chile, in 1986 to provide advance warning of locally
generated tsunami along this coastline within 2 min (Ber-
nard
1991
). When a sensor placed on the seabed detects a
seismic wave above a certain threshold, it transmits a
signal to the GEOS geostationary satellite, which then
relays a message to ground stations. The signal is pro-
cessed, and another signal is transmitted via the satellite to
far,
far
away.
Chile
is
one
of
those
faraway
countries,
but
with
a
significant
coastal
population.
In
