At a glance
Updated 31 March 2011 10:45 AM BST
The 9-magnitude quake which struck Japan on Mar. 11, 2011, was the largest tremor to hit the country since records began 140 years ago. It generated a 10-metre-high tsunami that swept away everything in its path, triggered a Pacific-wide tsunami alert and raised fears of a nuclear catastrophe from damaged power plants.
Thousands have died and hundreds of thousands are without power and water.
The main tremor split highways, flattened buildings and ignited fires all over the northeastern Pacific coast. Because of Japan's sophisticated early warning systems, many people were able to escape the worst effects of the shaking. But the ensuing tsunami – which stretched several kilometres inland - wiped out entire villages and towns.
The coastal town of Otsuchi was one of the worst-hit. It was rattled by the massive earthquake and then flattened by the ensuing tsunami. Officials fear more than half the town's population of about 19,000 was buried under the rubble.
The country is battling to prevent a nuclear catastrophe after the Fukushima nuclear power complex, 240 km (150 miles) north of Tokyo, was damaged. Authorities set up a 20-km (12-mile) exclusion zone around the Fukushima Daiichi plant, amid fears of a major radiation leak.
Engineers have been working to prevent a meltdown in three reactors after a series of explosions.
The quake struck off-shore 81 miles (130 km) east of Sendai in Honshu at a depth of 15.2 miles (24 km), the U.S. Geological Survey said. The country has been rocked by a series of strong aftershocks.
Prime Minister Naoto Kan described it as the country's worst crisis since World War Two.
Earthquakes are common in Japan, one of the world's most seismically active areas. The country accounts for about 20 percent of the world's earthquakes of magnitude 6 or greater.
HUMANITARIAN CRISIS
Japan mobilised a massive rescue effort to deliver food, water and fuel, and pull stranded survivors from buildings and damaged homes.
Hundreds of thousands of people in the north are without power and water and many have taken shelter in evacuation centres set up in schools and stadiums to escape the near-freezing temperatures.
Tens of thousands have also been evacuated from an exclusion zone around the damaged Fukushima nuclear power plants.
Aid workers said the evacuation centres may need to stay open for up to three months.
Japan deployed tens of thousands of Self-Defense Force officers to search for missing people, and rescue workers from more than a dozen countries are searching northeastern coastal cities for survivors.
Dozens of countries have offered assistance, including China, Indonesia and the Afghan city of Kandahar.
But rescue and relief operations were hampered by continuous aftershocks, tsunami alerts and fires. Many areas remain isolated and unreachable, the United Nations said on Mar. 14.
And, even at the end of March, survivors lacked food, water and heating.
Early on, U.S. warships and planes helping relief efforts moved away from Japan's Pacific coast temporarily because of low-level radiation from the damaged plants.
PACIFIC-WIDE TSUNAMI ALERT
Reviving memories of the giant tsunami that struck Asia in 2004, a major alert was issued to most countries in the Pacific basin on Mar. 11.
Within three minutes of the earthquake, the Japanese Meteorological Agency issued a tsunami warning, and people were told to escape to higher ground. Six minutes later warnings or watches were issued for islands from the South Pacific to Hawaii, as well as Russia. In the following hours the tsunami waves were tracked across the Pacific and warnings were issued for North and South America.
Many developing countries have beefed up early warning systems and evacuation plans since the 2004 tsunami. But the International Federation of Red Cross and Red Crescent Societies said the tsunami was higher than some of the Pacific islands it could wash over, warning that developing countries in the Asia Pacific region were particularly vulnerable to tsunami damage.
But by 1500 GMT on Mar. 11, there had been no reports of a serious tsunami hitting anywhere beyond Japan.
