The Boxing Day Tsunami in 2004 occurred because an underwater fault ruptured, causing one of the tectonic plates to be thrust upwards, which displaced the ocean above it and caused it to ripple outwards. The initial estimate of the magnitude of the earthquake which caused the tsunami was 8.8.
As of 2006, the estimate had been revised to between 9.1 and 9.3 magnitude, which made it the third-largest earthquake ever recorded. The tsunami spread out from the fault, affecting southeast Asia, Sri Lanka, Indonesia, Somalia and many other places. The U.S. Geological Survey estimated that 227,898 people died in the disaster, making it one of the 10-worst earthquakes and the worst tsunami ever recorded, in terms of casualties.