Introduction - Tsunami - page 2

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Introduction

1.1 Introduction

T ¯hoku Tsunami, it killed over 18,000 people; but more
strikingly, it rendered the cooling system of the Fukushima
Daiichi Nuclear Power Plant inoperable, leading to hydro-
gen explosions at three of its six reactors. The explosions
spread lethal contamination more than 60 km away, the
effects of which will last for decades (Earthquake Engi-
neering Research Institute 2011 ). The greatest risk to the
reactors had been assessed by senior engineers as being
from an earthquake. Junior engineers believed that the
greatest risk was from a tsunami, but their superiors insisted
that this risk was unrealistic and did not take the prediction
seriously.
The tsunami was the largest along the Sanriku coast in
over a thousand years. And this is one of the problems with
tsunami science. The severest tsunami disasters are very
rare; the risk increases dramatically with decreasing prob-
ability of occurrence (Harbitz et al. 2012 ). However, these
probabilities are difficult to predict based on historical
observations that may cover only a few hundred years.
Hence the urgent need for paleo-studies—studies based
upon the geological record. For example, there is geological
evidence for tsunami of a similar magnitude, or larger than,
the Indian Ocean and T ¯hoku Tsunami along apparently
aseismic and protected coastlines such as eastern Australia,
eastern Scotland and the Bristol Channel of western Britain.
These types of events have not only been repetitive, but in
some cases also overlap with historical records, namely in
Great Britain. In Australia, paleo-tsunami appear novel
because they have occurred in a country without a long,
scientifically based, written history or record of tsunami.
Aboriginal legends, however, orally record their occur-
rence. The generation of these tsunami is contentious, but
most likely due to either great submarine landslides or the
impact of asteroids and comets with the Earth's oceans.
The recent occurrence of large tsunami and discoveries
have serious implications when it is realised that Western
Civilization is unique in its settlement of the shoreline and
its development of great coastal cities. If a submarine
landslide generated a near-coastal tsunami off the coasts of

A tsunami is a wave, or series of waves in a wave train,
generated by the sudden, vertical displacement of a column
of water. This displacement can be due to seismic activity,
explosive volcanism, a landslide above or below water, an
asteroid impact, or certain meteorological phenomena.
These waves can be generated in oceans, bays, lakes, rivers,
or reservoirs. The term tsunami is Japanese and means
harbor (tsu) wave (nami), because such waves often develop
as resonant phenomena in harbors after offshore earth-
quakes. Both the singular and plural of the word in Japanese
are the same. Many English writers write the plural of
tsunami as tsunamis. The Japanese usage will be adhered to
throughout this text.
Before 1990, the public perceived tsunami as originating
primarily from large, distant, underwater earthquakes—
mainly in the Pacific Ocean. The fear of tsunami was
allayed by the knowledge that an early warning system
existed to prevent loss of life. In the 1990s, fourteen major
tsunami events struck the world's coastlines. While other
disasters over this period have caused more deaths and
greater economic destruction, these tsunami events have
made scientists aware that the tsunami hazard is pervasive.
The tsunami occurred as near-coastal events—generated by
small earthquakes or even submarine landslides—and in
many cases with minimal warning to local inhabitants.
These perceptions suffered a major shock on December 26,
2004 when one of the largest earthquakes ever recorded,
centered off the coast of northern Indonesia, generated a
tsunami that swept across the northern Indian Ocean and
killed hundreds of thousands of unsuspecting people. Big
tsunami can occur without warning in a world where
technology is supposed to save everyone. This point was
proven poignantly on March 11, 2011 in Japan, one of the
most technologically advanced countries in the world and
no stranger to tsunami. Here, one of the largest tsunami
generated by an earthquake ever recorded struck Sanriku on
the northeastern coast of Honshu Island. Known as the