INDIAN OCEAN TSUNAMI
Seismic Hazard Case Study (2004)
BACKGROUND & CAUSES
The Event: On Boxing Day, December 26th, 2004, a massive megathrust earthquake with a
magnitude between 9.1 and 9.3 struck off the west coast of Sumatra, Indonesia.
Tectonic Setting: The earthquake occurred along a destructive (convergent) plate boundary,
where the Indo-Australian Plate is subducting beneath the Eurasian Plate (specifically the Sunda
Plate) at the Sunda Trench.
Nature of the Tsunami: The immense pressure build-up caused the seafloor to snap upward by
up to 15 metres along a 1,500 km fault line. This sudden vertical displacement displaced billions
of tonnes of water, generating a series of catastrophic tsunami waves that radiated across the
Indian Ocean at speeds of up to 800 km/h in deep water.
PRIMARY IMPACTS
• Catastrophic Loss of Life: An estimated 230,000 people died across 14 different countries,
with Indonesia (especially the Aceh province), Sri Lanka, India, and Thailand suffering the
heaviest casualties.
• Coastal Devastation: Waves reaching up to 30 metres in height completely obliterated
coastal settlements, infrastructure, and natural defenses like mangrove forests.
• Displacement: Around 1.7 million people were made homeless instantly as entire villages
were swept away by the sheer force of the water.
SECONDARY IMPACTS
• Economic Collapse: Vital local industries were destroyed. The fishing industry lost boats,
nets, and harbours, while the tourism industry collapsed just as it was entering its peak
season, destroying thousands of livelihoods.
• Environmental Damage: Saltwater intrusion contaminated vital freshwater supplies and
poisoned agricultural land, rendering the soil infertile for years.
• Health Crisis: The destruction of sanitation networks and the presence of unburied bodies
and stagnant water led to severe risks of water-borne diseases such as cholera and
dysentery.
Seismic Hazard Case Study (2004)
BACKGROUND & CAUSES
The Event: On Boxing Day, December 26th, 2004, a massive megathrust earthquake with a
magnitude between 9.1 and 9.3 struck off the west coast of Sumatra, Indonesia.
Tectonic Setting: The earthquake occurred along a destructive (convergent) plate boundary,
where the Indo-Australian Plate is subducting beneath the Eurasian Plate (specifically the Sunda
Plate) at the Sunda Trench.
Nature of the Tsunami: The immense pressure build-up caused the seafloor to snap upward by
up to 15 metres along a 1,500 km fault line. This sudden vertical displacement displaced billions
of tonnes of water, generating a series of catastrophic tsunami waves that radiated across the
Indian Ocean at speeds of up to 800 km/h in deep water.
PRIMARY IMPACTS
• Catastrophic Loss of Life: An estimated 230,000 people died across 14 different countries,
with Indonesia (especially the Aceh province), Sri Lanka, India, and Thailand suffering the
heaviest casualties.
• Coastal Devastation: Waves reaching up to 30 metres in height completely obliterated
coastal settlements, infrastructure, and natural defenses like mangrove forests.
• Displacement: Around 1.7 million people were made homeless instantly as entire villages
were swept away by the sheer force of the water.
SECONDARY IMPACTS
• Economic Collapse: Vital local industries were destroyed. The fishing industry lost boats,
nets, and harbours, while the tourism industry collapsed just as it was entering its peak
season, destroying thousands of livelihoods.
• Environmental Damage: Saltwater intrusion contaminated vital freshwater supplies and
poisoned agricultural land, rendering the soil infertile for years.
• Health Crisis: The destruction of sanitation networks and the presence of unburied bodies
and stagnant water led to severe risks of water-borne diseases such as cholera and
dysentery.
