Where: In the Indian Ocean. In between Sri Lanka and Indonesia, but closer to Indonesia and the Andaman and Nicobar Islands.
It occurred the 26 of December 2004, the magnitude was 9.2 for 5 minutes. It has been said to be one of the most powerful earthquakes for 100 years.
It was caused by the a fault rupture on the subduction zone of the Indian (Eurasian) plate and the Sunda plate (Indonesian plate). It has been recorded that the epicentre was 20km under the sea, and 250km off the the coast if Indonesia, near the city of Banda Ache.
Primary Effects: The tsunami came at high speed across the Indian Ocean affecting at least 12 nations, Indonesia suffering the greatest. Around 250,000 people died with millions homeless. Aceh, which was close to the epicentre, was particularly affected by the tsunami because it lies low so the waves came up to a mile inland. 131,000 people were confirmed dead and 37,000 people missing. More than 80,000 houses were damaged or collapsed. As well as the massive damaging to housing, utilities, roads and bridges, the disaster disrupted the communities and the government of affected areas.
Secondary effects: Spread of diseases such as cholera, dysentery and diphtheria due to contaminated water and tropical climate. Loss of coastal fishing industries. Loss of tourism revenue from areas such as Thailand. Emotional and psychological effects of the locals and health care workers. Many orphans left due to children surviving without their parents.
http://www.docstoc.com/docs/6065899/The-Sumatra-Earthquake-and-Indian-Ocean-Tsunami-Case-Study