source: anuga_work/publications/boxing_day_validation_2008/data.tex @ 7463

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2The sheer magnitude of the 2004 Sumatra-Andaman earthquake and the
3devastation caused by the subsequent tsunami have generated much
4scientific interest. As a result an unusually large amount of post
5seismic data has been collected and documented. Data sets from
6seismometers, tide gauges, \textsc{gps} surveys, satellite overpasses,
7subsequent coastal field surveys of run-up and flooding, and
8measurements of coseismic displacements as well as bathymetry from ship-based
9expeditions, have now been made
10available. %~\cite{vigny05,amnon05,kawata05,liu05}. FIXME (Ole): Refs?  Are the references here inappropriate?
12In this section we present the corresponding data necessary to implement
13the proposed benchmark. Here we note that the overwhelming focus of tsunami
14modelling is the prediction of inundation extent. The ``fit'' of observed and
15 modelled runup should have the greatest influence on conclusions regarding
16model validity. In fact for non-physics based models it may not be possible
17 to validate the generation and propagation phases of tsunami evolution.
18However, for physics-based models evaluation of the model during the generation
19 and propagation phases is still useful. If a model is physics-based one
20should ensure that all physics are being modelled accurately. Moreover
21evaluation of all three stages of tsunami evolution can help identify the
22cause of any discrepancies between modelled and observed inundation.
23Consequently in this section we present data not only to facilitate
24validation of inundation but to also aid the assessment of tsunami
25generation and propagation.
28All tsunami are generated from an initial disturbance of the ocean
29which develops into a low frequency wave that propagates outwards from
30the source. The initial deformation of the water surface is most
31commonly caused by coseismic displacement of the sea floor, but
32submarine mass failures, landslides, volcanoes or asteroids can also
33cause tsunami. In this section we detail the information used in
34this study to validate models of the sea floor deformation generated
35by the 2004 Sumatra--Andaman earthquake.
37The 2004 Sumatra--Andaman tsunami was generated by a coseismic
38displacement of the sea floor resulting from one of the largest
39earthquakes on record. The mega-thrust earthquake started on the 26
40December 2004 at 0h58'53'' UTC (or just before 8 am local time)
41approximately 70 km offshore of North Sumatra
42(\url{}). The
43rupture propagated 1000-1300 km along the Sumatra-Andaman trench to
44the north at a rate of 2.5-3 km.s$^{-1}$ and lasted approximately 8-10
45minutes~\cite{ammon05}. Estimates of the moment magnitude of this
46event range from about 9.1 to 9.3 $M_w$~\cite{chlieh07,stein07}.
48The unusually large surface deformation caused by this earthquake
49means that there were a range of different geodetic measurements of
50the surface deformation available. These include field measurements of
51uplifted or subsided coral heads, continuous or campaign \textsc{GPS}
52measurements and remote sensing measurements of uplift or subsidence
53(see~\cite{chlieh07} and references therein). Here we use the the near-field
54estimates of vertical deformation in northwestern Sumatra and
55the Nicobar-Andaman islands collated by~\cite{chlieh07} to assess whether
56our crustal deformation model of the 2004 Sumatra--Andaman
57earthquake is producing reasonable results. Note that the geodetic
58data used here is a combination of the vertical deformation that
59happened in the $\sim$10 minutes of the earthquake plus the
60deformation that followed in the days following the earthquake before
61each particular measurement was actually made (typically of order
62days). Therefore some of the observations may not contain the purely
63co-seismic deformation but could include some post-seismic deformation
64as well~\cite{chlieh07}.
67\label{sec:propagation data}
68Once generated, a tsunami will propagate outwards from the source until
69it encounters the shoreline bordering coastal regions. This period
70of the tsunami evolution is referred to as the propagation stage. The
71height and velocity of the tsunami is dependent on the local
72bathymetry in the regions through which the wave travels and the size
73of the initial wave. This section details the bathymetry data needed
74to model the tsunami propagation and the satellite altimetry transects
75used here to validate open ocean tsunami models.
77\subsubsection{Bathymetry Data}\label{sec:bathymetry data}
78The bathymetry data used in this study was derived from the following
81\item a two arc minute grid data set covering the Bay of Bengal,
82  DBDB2, obtained from US Naval Research Labs
83  (\url{});
84\item a 3 second arc grid covering the whole of the Andaman Sea based
85  on Thai Navy charts no. 45 and no. 362; and 
86  (FIXME (OLE): wait for DB's reply)
87\item a one second grid created from the digitised Thai Navy
88  bathymetry chart, no. 358, which covers Patong Bay and the
89  immediately adjacent regions.
90  The gridding of data was performed using {\bf Intrepid}, a commercial
91  geophysical processing package developed by Intrepid Geophysics. The
92  gridding scheme employed the nearest neighbour algorithm followed by
93  an application of minimum curvature akima spline smoothing.
94  See \url{} 
95  for details on the Intrepid model. 
98These sets were combined via
99interpolation and resampling to produce four nested grids
100which are relatively coarse in the deeper water and
101progressively finer as the distance to
102Patong Beach decreases as shown in Figure~\ref{fig:nested_grids}
104The coarsest
105bathymetry was obtained by interpolating the DBDB2 grid to a 27 second
106arc grid. A subsection of this region was then replaced by nine second
107data which was generated by sub-sampling the three second of arc grid from
108NOAA. It is an artificially generated data set which is a subset of the original data.
110A subset of the nine second grid was replaced by the three second
111data. Finally, the one second grid was used to approximate the
112bathymetry in Patong Bay and the immediately adjacent regions. Any
113points that deviated from the general trend near the boundary were
114deleted as a quality check.
116A one second grid was used to approximate the bathymetry in Patong
117Bay. This elevation data was created from the digitised Thai
118Navy bathymetry chart, no 358. The digitised points and contour lines
119from this chart are shown in Figure~\ref{fig:patong_bathymetry}.
122The sub-sampling of larger grids was performed by using {\bf resample},
123a Generic Mapping Tools (\textsc{GMT}) program (\cite{wessel98}).
129\caption{Nested bathymetry grids.}
134\subsubsection{JASON Satellite Altimetry}\label{sec:data_jason}
135During the 26 December 2004 event, the \textsc{jason} satellite tracked from
136north to south and over the equator at 02:55 UTC nearly two hours
137after the earthquake \cite{gower05}. The satellite recorded the sea
138level anomaly compared to the average sea level from its previous five
139passes over the same region in the 20-30 days prior. This data was
140used to validate the propagation stage in Section
144%DB I suggest we combine with model data to reduce the number of figures. The satellite track is shown in Figure~\ref{fig:satelliteTrack}.
147\label{sec:inundation data}
148Inundation is the final stage of the evolution of a tsunami and
149refers to the run-up of tsunami onto land. This process is typically the most
150difficult of the three stages to model due to thin layers of water
151flowing rapidly over dry land.  Aside from requiring robust solvers
152which can simulate such complex flow patterns, this part of the
153modelling process also requires high resolution and quality elevation
154data which is often not available. In the case of model validation
155high quality field measurements are also required. For the proposed
156benchmark a high resolution (1 second) topography data set and a
157tsunami inundation survey map from the
158Coordinating Committee Co-ordinating Committee for Geoscience Programmes
159in East and Southeast Asia (CCOP) (\cite{szczucinski06}) was obtained
160to validate model inundation. See also acknowledgements at the end of this paper. In this section we also present eye-witness accounts which can be used
161to qualitatively validate tsunami inundation.
163\subsubsection{Topography Data}
164The 1 second onshore topography for Patong Beach provided by the CCOP was
165merged with the nearshore 1 second bathymetry described in Section
166\ref{sec:bathymetry data} to provide a seamless terrain model for the
167bay and community as shown in Figure~\ref{fig:patong_bathymetry}.
173\caption{3D visualisation of the elevation data set used in Patong Bay showing data points, contours, rivers and roads draped over the final model.}
177FIXME (Jane): legend? Were the contours derived from the final dataset?
178This is not the entire model, only the bay and the beach. RICHARD
180\subsubsection{Buildings and Other Structures}
181Human-made buildings and structures can significantly affect tsunami
182inundation. The footprint and number of floors of the
183buildings in Patong Bay were extracted from a GIS data set which was also provided by the CCOP (see Section \ref{sec:inundation data} for details).
184The heights of these
185buildings were estimated assuming that each floor has a height of 3 m and they
186were added to the topographic dataset.
188\subsubsection{Inundation Survey}
189Tsunami run-up in built-up areas can be the cause of large financial and human
190losses, yet run-up data that can be used to validate model run-up
191predictions is scarce because such events are relatively infrequent.
192Of the two field benchmarks proposed
194only the Okushiri benchmark facilitates comparison between
195modelled and observed run-up. One of the major strengths of the
196benchmark proposed here is that modelled run-up can be compared to an
197inundation survey which maps the maximum run-up along an entire coastline
198rather than at a series of discrete sites. The survey map is
199shown in Figure~\ref{fig:patongescapemap} and plots the maximum run-up
200of the 2004 Indian Ocean tsunami in Patong city. Refer to Szczucinski et
201al~\cite{szczucinski06} for further details.
207\caption{Tsunami survey mapping the maximum observed inundation at
208  Patong beach courtesy of the CCOP \protect \cite{szczucinski06}.}
214\subsubsection{Eyewitness Accounts}\label{sec:eyewitness data}
215Eyewitness accounts detailed in~\cite{papadopoulos06}
216report that many people at Patong Beach observed an initial
217retreat (trough or draw down) of
218the shoreline of more than 100 m followed a few minutes later by a
219strong wave (crest). Another less powerful wave arrived another five
220or ten minutes later. Eyewitness statements place the arrival time of
221the first wave between 9:55 am and 10:05 am local time or about 2 hours
222after the source rupture.
223FIXME (Ole): We should add observed arrival time and later relate that to
224the modelled dynamics. Wait for Drew's updated animation.
231\caption{Location of timeseries extracted from the model output. FIXME(John):
232should we combine the inundation map with the gauages map?}
237Two videos were sourced\footnote{The footage is
238widely available and can, for example, be obtained from
240(Comfort Hotel) and
244which include footage of the tsunami in Patong Bay on the day
245of the 2004 Indian Ocean Tsunami. Both videos show an already inundated
246group of buildings. They also show what is to be assumed as the second
247and third waves approaching and further flooding of the buildings and
248street.  The first video is in the very north, filmed from what is
249believed to be the roof of the Novotel Hotel marked ``north'' in Figure
250\ref{fig:gauge_locations}. The second video is in the very south,
251filmed from the second story of a building next door to the Comfort
252Resort near the corner of Ruam Chai St and Thaweewong Road.  This
253location is marked ``south'' in Figure \ref{fig:gauge_locations}.
254Figure~\ref{fig:video_flow} shows stills from this video. Both videos
255were used to estimate flow speeds and inundation depths over time.
263\caption{Four frames from a video where flow rate could be estimated,
264  circle indicates tracked debris, from top left: 0.0 sec, 5.0 s, 7.1
265  s, 7.6 s.}
270Flow rates were estimated using landmarks found in both videos and
271were found to be in the range of 5 to 7 metres per second (+/- 2 m/s)
272in the north and 0.5 to 2 metres per second (+/- 1 m/s) in the
273south\footnote{These error bounds were estimated from uncertainty in aligning the debris with building boundaries in the videos.}.
274Water depths could also
275be estimated from the videos by the level at which water rose up the
276sides of buildings such as shops. Our estimates are in the order of
2771.5 to 2.0 metres (+/- 0.5 m estimated error bounds).
278Fritz ~\cite{fritz06} performed a detailed
279analysis of video frames taken around Banda Aceh and arrived at flow
280speeds in the range of 2 to 5 m/s.
283\subsection{Validation Check-List}
285The data described in this section can be used to construct a
286benchmark to validate tsunami models.
287 In particular we propose that a legitimate tsunami model
288should reproduce the following behaviour:
290 \item reproduce the inundation survey map in Patong city
291   (Figure~\ref{fig:patongescapemap}),
292 \item simulate a leading depression followed by two distinct crests
293   of decreasing magnitude at the beach, and
294 \item predict the water depths and flow speeds, at the locations of
295   the eye-witness videos, that fall within the bounds obtained from
296   the videos.
297 \item reproduce the \textsc{jason} satellite altimetry sea surface
298   anomalies (see Section~\ref{sec:data_jason}),
299 \item reproduce the vertical deformation observed in north-western
300   Sumatra and along the Nicobar--Andaman islands (see
301   Section~\ref{sec:gen_data}),
304Ideally, the model should also be compared to measured timeseries of
305waveheights and velocities but the authors are not aware of the
306availability of such data near Patong Bay.
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