Powerful earthquakes followed by tsunami watches and warnings had residents in Indonesia on high alert Wednesday. For some, it was far too similar to the devastation the region faced eight years ago.
December 26, 2004 - An earthquake with an estimated magnitude of between 9.1 to 9.3 strikes the coast of Sumatra, Indonesia.
Tsunamis are formed by a displacement of water -- a landslide, volcanic eruption, or, as in this case, slippage of the boundary between two of the earth's tectonic plates -- slabs of rock 50 to 650 feet (15 to 200 km) thick that carry the Earth's continents and seas on an underground ocean of much hotter, semi-solid material.
The December 26, 2004 Indian Ocean tsunami was caused by slippage of about 600 miles (1,000 km) of the boundary between the India and Burma plates off the west coast of northern Sumatra.
The convergence of other plates strains the area, and at the quake's epicenter, the India plate is moving to the northeast at 2 inches (5 cm) per year relative to the Burma plate.
The aftershocks were distributed along the plate boundary from the epicenter to near Andaman Island.
Death Toll: 227,898