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5. DISCUSSION OF SURVEY RESULTS
5.1. Runup, Inundation, Arrival Time
The maximum positive amplitude of tsunami near the shoreline has been measured by following the information obtained from eyewitness interviews and/or field measurements of tsunami traces at Medan, Simeulue and Meulaboh. At all coastal locations where we have surveyed, the tsunami have much more inundated towards inland along the rivers.
The waves have arrived Medan 4 hours after the earhquake with an average positive amplitude of 1.5m.
The eyewitnesses have reported that sea receded about 500 m and advanced with an approximate amplitude of 1-1.5m ten minutes after the earthquake. Half an hour after that the second (but) destrcutive wvae has arrived. The third wave was also destructive and arrived 50-60 minutes after the previous (second) wave. We have observed that the extensive inundation of tsunami waves at north west coast of Sumatra Island started at a location about 30 km south of Meulaboh city. The maximum positive amplitude of tsunami waves have been observed by eyewitnesses as higher than 15m. near Meulaboh. The inundation distance is about 5 km.
The people living in Simeulue Island were very sensitive about the sea motion after the earthquake snce 1907 when a tsnami hit western coast of Island. Only 8 people died in the island out of 78000 population. The hardest hit was at north of Island. There was weak wave action at east side of island especially at North of Tanjun Raya.
In Figure 7, the distribution of Runup at several coastal locations near the coast of Indian Ocean is presented. The figure is drawn by compilation of results of several field surveys in the region published or publicized in Fritz H. and Synolakis C., (2005), Gusiakov S., (2005), Kawata Y. et. al., (2005), Shibayama et. al., (2005), Synolakis C., and Borrero J., (2005) Taymaz et. al., (2005), Tsuji Y. et. al., (2005), Yalciner et. al. , (2005), Yeh (2005),
Figure 7. The Runup Distributions at North Sumatra Coats (Indonesia), Thailand, India, Sri Lanka, Maldives Measured by Indonesian, Japanese, Russian, Turkish and USA Scientists.
5.2. The Response of Structures Against Tsunami Attack
The structural response can be analysed for two types of structures
- Wooden Stuctures
- Conrete Structures
iii. Infrastructures
5.2.1. Wooden Stuctures
The wooden structures has been constructed on a concrete ground base. It is clearly observed that tsunami has swept the wooden part of the structures and completely damaged them where the flow depth exceeded 2.5-3 m in the inundation region. The photographs in Figure 7 show the typical damages and damage levels of tsunami on wooden structures.
Figure 7: The typical damages and damage levels of tsunami on wooden structures.
5.2.2. Concrete Stuctures
The concrete structures have standed against tsunami waves. But their level of resistance and success for survival are fully dependent on i. the percent of open area (area of windows) on the walls of ground floor for tsunami transmission and also ii. The flow depth of tsunamis near the structure. The scour around the concrete sturctures are the common effect of flow velocities related to tsunami action. The photographs in Figure 8 show the typical damages and damage levels of tsunami on concrete structures.
Figure 8: The typical damages and damage levels of tsunami on concrete structures.
5.2.3. Infrastructures
Mainly the cities are located the shoreline in Sumatra. Most of the villages near the cities at north of Sumatra are located near the coastline (in the range of 1-2 km from the shoreliine). The main components of transportation between the cities and villages are land transportation on roads, bridges and partly betwen harbors as maritime transportation. This type of land use plans have resulted the effects of tsunami waves to be much more destructive and devastating on either accomodation structures or transportation infrastructures
Figure 9: The Typical Damages and Damage Levels of Tsunami on Infrastructures
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