source: anuga_work/production/dampier_2006/report/modelling_methodology.tex @ 3988

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2The Risk Research Group aims to define the economic and social threat posed to urban communities
3by a range of rapid onset natural hazards. Through the integration of natural hazard research, defining national exposure and
4estimating socio-economic vulnerabilities, predictions of the likely impacts of events can be made.
5By modelling the likely impacts on urban communities as accurately as possible and
6building these estimates into land use planning and emergency
7management, communities will be better prepared to respond to
8natural disasters when they occur.
11%GA bases its risk modelling on the process of understanding the hazard and a community's
12%vulnerability in order to determine the impact of a particular hazard event.
13%The resultant risk relies on an assessment of the likelihood of the event.
14%An overall risk assessment for a particular hazard would then rely on scaling
15%each event's impact by its likelihood.
17To develop a tsunami risk assessment,
18the tsunami hazard itself must first be understood. These events are generally modelled by converting
19the energy released by a subduction earthquake into a vertical displacement of the ocean surface.
20%Tsunami hazard models have been available for some time.
21The resulting wave is
22then propagated across a sometimes vast stretch of ocean towards the
23area of interest.
24%using a relatively coarse model
25%based on bathymetries with a typical resolution of two arc minutes.
26Initial hazard assessments have been based on reporting the maximum wave height at a fixed contour line near the coastline,
27(e.g. 50m). This is how the preliminary tsunami hazard assessment was reported by GA
28to FESA in September 2005 \cite{BC:FESA} for a suite of Mw 9 earthquakes
29evenly spaced along the Sunda Arc subduction zone.
30The assessment used the Method of Splitting Tsunamis (MOST)
31\cite{VT:MOST} model. Subsequent hazard assessments are been developed in a
32probabilistic manner which are being derived from the URS Corporation's
33Probabilistic Tsunami Hazard Analysis model \cite{somerville:urs}.
34%The maximal wave height at a fixed contour line near the coastline
35%(e.g. 50m) is then reported as the hazard to communities ashore.
36%Models such as Method of Splitting Tsunamis (MOST) \cite{VT:MOST} and the
37%URS Corporation's
38%Probabilistic Tsunami Hazard Analysis 
39%\cite{somerville:urs} follow this paradigm.
41While MOST and URS are suitable for generating and propagating the tsunami wave from its source, it is not adequate to
42model the wave's impact on communities ashore. 
43To capture the \emph{impact} of a tsunami to a coastal community,
44the model must be capable of capturing more detail about the wave,
45particularly how it is affected by the local bathymetry, as well as the
46local topography as the wave moves onshore.
47%the details of how waves are reflected and otherwise
48%shaped by the local bathymetries as well as the dynamics of the
49%runup process onto the topography in question.
50It is well known that local bathymetric and topographic effects are
51critical in determining the severity of a hydrological disaster
52\cite{matsuyama:1999}. To model the impact of the tsunami wave on the
53coastal community, we use ANUGA \cite{ON:modsim}. In order to capture the
54details of the wave and its interactions, a much finer resolution is
55required than that of the hazard model. As a result, ANUGA simulations concentrate
56on specific coastal communities. MOST and URS by contrast use a
57coarser resolution and covers often vast areas. To develop the impact
58from an earthquake event from a distant source, we adopt a hybrid approach of
59modelling the event itself with the URS model and modelling the impact with ANUGA.
60In this way, the output from URS serves as an input to ANUGA.
61In modelling terms, the URS output is a boundary condition for ANUGA.
63The event chosen for this study has been determined from the probabilistic
64hazard modelling being undertaken by the Earthquake and Hazards Project.
65The low probability, high potential impact Mw 9.0 event has been chosen
66for this study.
70  %\centerline{ \includegraphics[width=140mm, height=100mm]
73%  \caption{Maximum wave height (in cms) for a Mw 9.0 event off the
74%coast of Java}
75%  \label{fig:mw9}
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