Geoscience Reference
In-Depth Information
TSUNAMI HAZARD ASSESSMENT
Tsunami hazard assessments focus on characterizing and visualizing the physical charac-
teristics of future tsunamis (e.g., speed of onset, impact forces, currents, inundation area) that
can pose a threat to people and the things they value.
Understanding where tsunami inunda-
tion is likely and how much time at-risk individuals have to evacuate frame the discussion of
societal risk to tsunamis and are the foundations upon which education, preparedness plans,
response plans, and mitigation strategies are developed. Tsunami hazard assessments typi-
cally entail three elements: (1) inundation models to determine the areas likely to be looded,
(2) hazard maps that portray inundation-model outputs on community base maps (e.g., roads,
elevation, structures), and (3) evacuation maps that depict areas that may need to be evacu-
ated in the event of tsunamis. The purpose of this section is to describe each of these elements,
progress in the development and implementation of each element, and areas for improvement.
Before discussing each individually, it is important to distinguish the differences between
the three elements. For example, although hazard and evacuation maps are both used for re-
ducing tsunami risk, the two types of tsunami maps are developed in different ways and for dif-
ferent purposes (Figure 2.1). Inundation model outputs simply denote the physical character-
istics of tsunami generation, propagation, and inundation areas and do not recognize political
boundaries. Tsunami hazard maps portray inundation model outputs with some modiication
to relect local knowledge of land conditions, are organized by communities, and include basic
societal assets (e.g., roads, major structures). Tsunami evacuation maps incorporate the same
inundation areas as hazard maps, but typically denote larger zones to accommodate local risk
tolerance and to allow for easier identiication of landmarks (e.g., at-risk individuals can identify
major roads easier than a speciic elevation contour). Evacuation maps also differ from hazard
maps in that they are educational tools designed to be easily understood by non-scientists and
typically identify evacuation shelters and assembly sites (both natural and manmade), sug-
gested routes, locations of warning loudspeakers, and transportation infrastructure to facilitate
evacuations (e.g., streets, bridges). Inundation models and hazard maps are developed by sci-
entists to identify and communicate maximum inundation areas and low conditions, whereas
evacuation maps are designed by scientists in collaboration with local, state, and federal emer-
gency management and public safety agencies to identify areas of public safety concern.
Inundation Modeling
Credible tsunami inundation modeling requires three elements: (1) an understanding
of the tsunami source that generates the tsunami, usually through estimation of sealoor
displacement; (2) accurate and precise bathymetric and topographic data to understand the
surface over which the waves propagate; and (3) a robust hydrodynamic computational model
to simulate tsunami evolution. Each of these three elements are treated below in turn and offer
two sets of conclusions and recommendations—one on ways of reducing uncertainties about
tsunami sources and the other on hydrodynamic modeling.
