How large was the earthquake that caused the 2004 tsunami in the indian ocean?

"The undersea megathrust earthquake was caused when the Indian Plate was subducted by the Burma Plate and triggered a series of devastating tsunamis along the coasts of most landmasses bordering the Indian Ocean, killing 230,000-280,000 people in 14 countries, and inundating coastal communities with waves up to 30 metres (100 ft) high."