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2 | The Risk Research Group aims to define the economic and social threat posed to urban communities |
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3 | by a range of rapid onset natural hazards. Through the integration of natural hazard research, defining national exposure and |
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4 | estimating socio-economic vulnerabilities, predictions of the likely impacts of events can be made. |
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5 | By modelling the likely impacts on urban communities as accurately as possible and |
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6 | building these estimates into land use planning and emergency |
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7 | management, communities will be better prepared to respond to |
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8 | natural disasters when they occur. |
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9 | |
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10 | |
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11 | %GA bases its risk modelling on the process of understanding the hazard and a community's |
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12 | %vulnerability in order to determine the impact of a particular hazard event. |
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13 | %The resultant risk relies on an assessment of the likelihood of the event. |
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14 | %An overall risk assessment for a particular hazard would then rely on scaling |
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15 | %each event's impact by its likelihood. |
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16 | |
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17 | To develop a tsunami risk assessment, |
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18 | the tsunami hazard itself must first be understood. These events are generally modelled by converting |
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19 | the energy released by a subduction earthquake into a vertical displacement of the ocean surface. |
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20 | %Tsunami hazard models have been available for some time. |
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21 | The resulting wave is |
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22 | then propagated across a sometimes vast stretch of ocean towards the |
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23 | area of interest. |
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24 | %using a relatively coarse model |
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25 | %based on bathymetries with a typical resolution of two arc minutes. |
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26 | Initial hazard assessments have been based on reporting the maximum wave height at a fixed contour line near the coastline, |
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27 | (e.g. 50m). This is how the preliminary tsunami hazard assessment was reported by GA |
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28 | to FESA in September 2005 \cite{BC:FESA} for a suite of Mw 9 earthquakes |
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29 | evenly spaced along the Sunda Arc subduction zone. |
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30 | The assessment used the Method of Splitting Tsunamis (MOST) |
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31 | \cite{VT:MOST} model. Subsequent hazard assessments are been developed in a |
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32 | probabilistic manner which are being derived from the URS Corporation's |
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33 | Probabilistic Tsunami Hazard Analysis model \cite{somerville:urs}. |
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34 | %The maximal wave height at a fixed contour line near the coastline |
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35 | %(e.g. 50m) is then reported as the hazard to communities ashore. |
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36 | %Models such as Method of Splitting Tsunamis (MOST) \cite{VT:MOST} and the |
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37 | %URS Corporation's |
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38 | %Probabilistic Tsunami Hazard Analysis |
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39 | %\cite{somerville:urs} follow this paradigm. |
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40 | |
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41 | While MOST and URS are suitable for generating and propagating the tsunami wave from its source, it is not adequate to |
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42 | model the wave's impact on communities ashore. |
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43 | To capture the \emph{impact} of a tsunami to a coastal community, |
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44 | the model must be capable of capturing more detail about the wave, |
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45 | particularly how it is affected by the local bathymetry, as well as the |
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46 | local topography as the wave moves onshore. |
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47 | %the details of how waves are reflected and otherwise |
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48 | %shaped by the local bathymetries as well as the dynamics of the |
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49 | %runup process onto the topography in question. |
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50 | It is well known that local bathymetric and topographic effects are |
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51 | critical in determining the severity of a hydrological disaster |
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52 | \cite{matsuyama:1999}. To model the impact of the tsunami wave on the |
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53 | coastal community, we use ANUGA \cite{ON:modsim}. In order to capture the |
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54 | details of the wave and its interactions, a much finer resolution is |
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55 | required than that of the hazard model. As a result, ANUGA simulations concentrate |
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56 | on specific coastal communities. MOST and URS by contrast use a |
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57 | coarser resolution and covers often vast areas. To develop the impact |
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58 | from an earthquake event from a distant source, we adopt a hybrid approach of |
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59 | modelling the event itself with the URS model and modelling the impact with ANUGA. |
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60 | In this way, the output from URS serves as an input to ANUGA. |
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61 | In modelling terms, the URS output is a boundary condition for ANUGA. |
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62 | |
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63 | The event chosen for this study has been determined from the probabilistic |
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64 | hazard modelling being undertaken by the Earthquake and Hazards Project. |
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65 | The low probability, high potential impact Mw 9.0 event has been chosen |
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66 | for this study. |
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67 | |
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68 | %\begin{figure}[h] |
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69 | |
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70 | %\centerline{ \includegraphics[width=140mm, height=100mm] |
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71 | %{../report_figures/mw9.jpg}} |
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72 | |
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73 | % \caption{Maximum wave height (in cms) for a Mw 9.0 event off the |
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74 | %coast of Java} |
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75 | % \label{fig:mw9} |
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76 | %\end{figure} |
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77 | |
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78 | |
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79 | |
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