6. The Dec. 26, 2004 Tsunami Disaster in Indian Ocean

6. The December 26, 2004 Tsunami Disaster inIndian Ocean
6-1. Overview of the Earthquake and Tsunami
On Sunday morning, December 26, 2004, a devastating earthquake of the magnitude of 9.0
on the Richter scale (reported by USGS: United States Geological Survey) occurred at 07:58(Local Time/Western Indonesia Standard Time, UTC+0700), off the western coast of Northern
Sumatra, Indonesia. The hypocenter was located at 3.307 N, 95.947 E and some 10 km underthe seabed. This part is known as the subduction zone which the Indo-Australian Plate isthrusting under the Eurasia Plate. This earthquake is considered as a typical “reverse fault” oneat the plate boundary.

Fig. 6-1-1 Bathymetry and land topography in South Asia
The point “ “ is an epicenter of the earthquake on 26 December, 2004 (M9.0).
The point “×” is an epicenter of the earthquake on 28 March 2005 (M8.7).
(Developed by the Geographical Survey Institute of Japan)

The aftershocks of the earthquake on December 26, 2004 were distributed toward the northof the main quake, along the Andaman and Nicobar Islands (Fig. 6-1-2), according to theUSGS observations and reports. The length of the earthquake fault ran over 1,000 km from
north to south and triggered deadly powerful tsunamis which propagated mainly toward theeast and west directions (Fig. 6-1-3).

6. The Dec. 26, 2004 Tsunami Disaster in Indian Ocean

Fig. 6-1-2 The main shock and distribution of aftershocks(until January 29 2005, first 35 days) determined by the USGS.

Fig. 6-1-3 Estimated tsunami arrival times (every one hours) based on computer simulation(Developed by Dr. K. Satake, Active Fault Research Center, National Institute of Advanced
Industrial Science and Technology, Japan)
There were no reports regarding the direct damage by the ground motion, except the one
from Ache, Indonesia. (The Andaman and Nicobar Islands might also have been damaged by
the ground motion before the tsunami. However, there were no detailed reports on this matter.)
The ground motion was attenuated quickly with distance from the seismic source area. So,
many people were attacked by the tsunami without any strong ground motion in advance. The
length of the affected coastlines is considered to exceed 15,000 km (Fig. 6-1-4). An
international research group found the traces of a tsunami 40 m high or over along the west
coast of Sumatra. This is the most severely affected site because it is located very close to thehypocenter of the earthquake. A tsunami higher than 10 meters was also observed at the western
coast of Thailand. The tsunami reached the maximum height of 2 to 6 meters in Sri Lanka, India,Malaysia and Myanmar. Bangladesh, Maldives, Somalia, Kenya, Tanzania, Seychelles, andMadagascar also reported tsunami heights of 1 to 3 meters. (Each tsunami height is based on the6. The Dec. 26, 2004 Tsunami Disaster in Indian Ocean

interim report.) Every affected area was hit by the tsunami several times.

Fig. 6-1-4 Major coastal areas attacked by tsunami(Edited by the ADRC based on the GIS data developed by ESRI)The damage assessment process faced difficulties. For example, this wide-area disaster
affected over 10 countries around the Indian Ocean. The traffic network and communication
systems in these areas were destroyed. Some of the affected areas are politically unstable.
At first, the number of the dead and missing was estimated to exceed 280,000. Then, inApril 2005, the Government of Indonesia reported that the number of missing people were37,063, not 93,458. Now, the total number of the dead and missing is over 220,000.
The affected regions are principally the developing countries. It is difficult to assess theimpact by the disaster based only on the total amount of economic damages. To evaluate theactual impact on each society, the ADRC calculated the economic damages (interim)/GDP ratio
in each severely affected country (Table 6-1-1). The calculation result showed that the total
amount of economic damage in Maldives was smaller than that in Indonesia, Sri Lanka or India,
nearly equal to that in Thailand. However, the damage in Maldives was the worst in terms ofthe damage/GDP ratio
Table 6-1-1 International comparison on the economic damages (interim) / GDP ratio
Economic Damage /Country
Economic Damage (US$)
GDP(2002) (US$)
GDPMaldives
410,000,000
626,249,019
65.47%
Sri Lanka
1,000,000,000
16,567,132,195
6.04%
Indonesia
4,505,000,000
172,911,305,030
2.61%
Thailand405,200,000
126,905,108,610
0.32%
India
1,500,000,000
510,177,250,750
0.29%(Source: CRED EM-DAT, World Bank World Development Indicators)