Seismic Event: The Sumatra-Andaman Earthquake Flashcards
What’s the case study name
The Sumatra-Andaman earthquake (Boxing Day tsunami)
When and where was the earthquake
Epicentre off west coast of Sumatra, earthquake was 26 December 2004
Describe the event
Magnitude was 9.1-9.3 M(subscript W)
Duration was 8-10minutes
Linked events: Indian Ocean tsunami
Other features: daily aftershocks measuring up to 6.7M(subscript W) and lasting for 3 months
Tell me about the primary environmental impacts
There was a 10m movement laterally and 4-5m vertically along the fault line. The seabed rose by several metres, which displaced 30km^3 of water. This triggered a tsunami along the whole 1,600km length of subduction.
Banda Aceh province, the land mass closest to the epicentre of the earthquake, bore the full brunt. About 15 minutes after its eruption, the tsunami hit the west coast of Aceh. In some places, waves went inland 7.5km from the coastline.
Sri Lanka was the next worst affected because there was no other landmass between it and the epicentre. The waves hit over 2,260km of coastline in the east and north of Sri Lanka. In many areas, the walls of water were up to 10m high when they lashed against the shoreline. In some areas waves did not break, but continued inland as a fast stream of high water up to 5km from the coast.
Tell me about the secondary environmental impacts
The smaller islands southwest of Sumatra have moved southwest by about 20cm. Since movement was vertical as well as lateral, some coastal areas have been moved to below sea level.
The Andaman and Nicobar islands appear to have shifted southwest by around 1.25m (and have sunk by 1m)
The earthquake had a huge effect on the topography of the seabed. 1,500m high thrust ridges, created by previous geological activity along the fault, collapsed, generating submarine landslides several kilometres wide. One such landslide consisted of a single block of rock some 100m high and 2km long. The momentum of the water displaced by tectonic uplift also dragged massive slabs of rock, each weighing millions of tons, as far as 10km across the seabed. An oceanic trench several kilometres wide was created in the seabed.
Tell me about the primary social impacts
Indonesia was the worst affected area, with the death toll estimated to be as high as 220,000. Total casualties of 280,000 have been estimated
Eight people in South Africa died due to abnormally high sea levels and waves.
Relief agencies reported that one third of the dead were children. As many as four times more women than men were killed in some regions because they were waiting on the beach for the fisherman to return and looking after their children in the houses.
Up to 9,000 tourists (mostly Europeans) were among the dead or missing. Sweden’s death toll was 543
What were the secondary social impacts
1.8 million displaced people were spread over a dozen countries.
There was significant loss of housing
Diseases spread, eg malaria, dengue fever, cholera and typhoid as well as ‘tsunami lung’
Cash for work programmes contributed to the reconstruction effort while providing jobs and prompting social development. Many women participating in such programmes received the same wages as men, for the first time.
What were the secondary economic impacts
The total economic cost of damage was estimated at $9.4 billion US. In Aceh, the cost of damage ($4.5 billion) was almost equal to the country’s GDP in the previous year
What were the primary political impacts
Sri Lanka’s civil war was halted temporarily as both sides helped in the rescue, recovery and the initial rebuilding phase following the tsunami.
What were the secondary political impacts
Aceh had seen conflict between separatists and the government for 30 years. When the waves hit, fighting ceased as the parties became focused on the more immediate struggle for survival. In August 2005 a peace agreement was called for separatists to surrender their weapons and the government to withdraw its troops. This process was completed by December that year.
Tell me about risk management: preparedness
Despite a time lag of up to several hours between the earthquake and the impact of the tsunami in some parts of the Indian Ocean, nearly all of the victims were taken completely by surprise. There was no tsunami warning system in the Indian Ocean to warn the general population living around it. Tsunami detection is not easy because while a tsunami is in deep water, it has little height and a network of sensors is needed to detect it. Setting up the communications infrastructure to issue timely warnings is an even bigger problem, particularly in a relatively poor part of the world.
Tell me about the risk management: prevention
There is a close connection between the magnitude of the damage the tsunami caused and poor coastal management. The high loss of life was partly a result of the destruction of natural defences, such as coral forests and mangrove swamps, and the building of oceanfront hotels and villas. For instance, the effects of the tsunami were less severe in areas along the east coast of Aceh, where the coastal ecosystem remained relatively untouched. In Sri Lanka the damage was very severe in coastal areas where there had been violation of regulations prohibiting the mining of coral reefs, and destruction of coastal mangrove forests, which act as a buffer against high waves.
Tell me about the mitigation strategies
A tsunami warning system became active in June 2006, following the leadership of UNESCO. It consists of 25 seismographic stations and three deep ocean sensors, which relay information to the 26 national tsunami management centres.
Tell me about the adaptation strategies
The mobilisation of humanitarian aid ($14 billion) was the largest ever international response to a natural disaster. The number of donor countries and humanitarian organisations involved were also far greater than in any previous natural disaster.
Providing jobs such as rebuilding houses and weaving rope used in fishing nets has given income to farm workers who expected to miss a years work due to the seawater inundation that rendered their farmland temporarily useless.
