Geoscience Reference
In-Depth Information
INTRODUCTION
Understanding risk is a prerequisite to effectively preparing and warning endangered
people of potential and imminent tsunamis. To that effect, oficials must understand in advance
(1) where and to what extent tsunami inundation may occur and the amount of time before
waves arrive, (2) the characteristics of the population and communities in tsunami-prone areas,
and (3) how prepared individuals and communities are for evacuation.
Risk, as used in this report, is a concept used to give meaning to things, forces, or circum-
stances that pose danger to people or what they value (see also Box 2.1). It takes into account
BOX 2.1
Deinitions
Risk
is a concept used to give meaning to things, forces, or circumstances that pose danger to
people or what they value. Risk descriptions are typically stated in terms of the likelihood of harm or
loss of a vulnerable thing or process (e.g., health of human beings or an ecosystem, personal property,
quality of life, ability to carry on an economic activity) due to a physical event (i.e., hazard) (National
Research Council, 1996a). Some researchers have used the term risk to quantify the likelihood of
future tsunamis, while others have deined it as a product of the probability of tsunami-attributable
social damage (e.g., buildings, lives, businesses) and the magnitude of that damage. Research shows
that managers, policy makers, and members of the public rarely deine risk as an objective calcula-
tion; instead, perceptions vary according to differences in awareness, experiences, and social context
(Fischhoff et al., 1984; Weichselgartner, 2001).
Hazard
is the physical characteristics of an event (e.g., tsunami: speed of onset, impact forces,
currents, inundation area) that can pose a threat to people and the things they value.
Vulnerability
is
the personal or situational conditions that increase the susceptibility of people
or resources to harm from the hazard.
Inundation
refers to the process of coastal looding due to tsunamis or storm waves regardless
of the impact to human activities.
Run-up height
is the vertical elevation of the most landward penetration of the tsunami wave
with respect to the initial sea level (igure opposite page). Run-up is a vertical distance, while inunda-
tion is a horizontal distance.
Inundation models
determine the areas likely to be looded by a tsunami and involve numerical
computations of tsunami evolution for speciic tsunami scenario or consider an ensemble of tsunami
scenarios that might affect the map area.
Hazard maps
depict inundation areas on base maps that typically include contours, imagery,
buildings, roads, and/or critical infrastructure and take into account local geologic knowledge.
Evacuation maps
depict areas that need to be evacuated in the event of a tsunami and to show
evacuation routes to safe havens. Evacuation maps are based on the same inundation zones in hazard
