Japan Earthquake & Tsunami of 2011: Facts and Information

On March 11, 2011, a magnitude-9 earthquake shook northeastern Japan, unleashing a savage tsunami.

The effects of the great earthquake were felt around the world, from Norway's fjords to Antarctica's ice sheet. Tsunami debris continues to wash up on North American beaches two years later.

Japan still recovering

In Japan, residents are still recovering from the disaster. Radioactive water was recently discovered leaking from the Fukushima Daiichi Nuclear Power Plant, which suffered a level 7 nuclear meltdown after the tsunami. Japan relies on nuclear power, and many of the country's nuclear reactors remain closed because of stricter seismic safety standards since the earthquake. Two years after the quake, about 300,000 people who lost their homes were still living in temporary housing, the Japanese government said.

 

Earthquake a surprise

The unexpected disaster was neither the largest nor deadliest earthquake and tsunami to strike this century. That record goes to the 2004 Banda-Aceh earthquake and tsunami in Sumatra, a magnitude-9.1, which killed more than 230,000 people. But Japan's one-two punch proved especially devastating for the earthquake-savvy country, because few scientists had predicted the country would experience such a large earthquake and tsunami.

Japan's scientists had predicted a smaller earthquake would strike the northern region of Honshu, the country's main island. Nor did they expect such a large tsunami. But there had been hints of the disaster to come. The areas flooded in 2011 closely matched those of a tsunami that hit Sendai in 869. In the decade before the 2011 Tohoku earthquake, a handful of Japanese geologists had begun to recognize that a large earthquake and tsunami had struck the northern Honshu region in 869. However, their warnings went unheeded by officials responsible for the country's earthquake hazard assessments. Now, tsunami experts from around the world have been asked to assess the history of past tsunamis in Japan, to better predict the country's future earthquake risk.

The cause

The 2011 Tohoku earthquake struck offshore of Japan, along a subduction zone where two of Earth's tectonic plates collide. In a subduction zone, one plate slides beneath another into the mantle, the hotter layer beneath the crust. The great plates stick and slip, causing earthquakes. East of Japan, the Pacific plate dives beneath the overriding Eurasian plate. The temblor completely released centuries of built up stress between the two tectonic plates, a recent study found.

The earthquake started on a Friday at 2:46 p.m. local time (5:46 a.m. UTC). It was centered on the seafloor 45 miles (72 kilometers) east of Tohoku, at a depth of 20 miles (32 km) below the surface. The shaking lasted about six minutes. [Infographic: How Japan's 2011 Earthquake Happened]

Early warning

Residents of Tokyo received a minute of warning before the strong shaking hit the city, thanks to Japan's earthquake early warning system. The country's stringent seismic building codes and early warning system prevented many deaths from the earthquake, by stopping high-speed trains and factory assembly lines. People in Japan also received texted alerts of the earthquake warning on their cellphones.

Deaths

More than 18,000 people were killed in the disaster. Most died by drowning.

Less than an hour after the earthquake, the first of many tsunami waves hit Japan's coastline. The tsunami waves reached run-up heights (how far the wave surges inland above sea level) of up to 128 feet (39 meters) at Miyako city and traveled inland as far as 6 miles (10 km) in Sendai. The tsunami flooded an estimated area of approximately 217 square miles (561 square kilometers) in Japan.

The waves overtopped and destroyed protective tsunami seawalls at several locations. The massive surge destroyed three-story buildings where people had gathered for safety. Near Oarai, the tsunami generated a huge whirlpool offshore, captured on video.

Nuclear meltdown

The tsunami caused a cooling system failure at the Fukushima Daiichi Nuclear Power Plant, which resulted in a level 7 nuclear meltdown and release of radioactive materials. About 300 tons of radioactive water continues to leak from the plant every day into the Pacific Ocean, affecting fish and other marine life.

The response

In the tsunami's aftermath, Japan's Meteorological Agency was criticized for issuing an initial tsunami warning that underestimated the size of the wave. The country recently unveiled a newly installed, upgraded tsunami warning system. In some regions, such as Miyagi and Fukushima, only 58 percent of people headed for higher ground immediately after the earthquake, according to a government study. Many people also underestimated their personal risk, or assumed the tsunami would be as small as ones they had previously experienced, the study found.

Scientists from around the world descended on Japan following the earthquake and tsunami. Researchers sailed offshore and dropped sensors along the fault line to measure the forces that caused the earthquake. Teams studied the tsunami deposits to better understand ancient sediment records of the deadly waves. Earthquake engineers examined the damage, looking for ways to build buildings more resistant to quakes and tsunamis. Studies are ongoing today.

Worldwide effects

The tsunami waves also traveled across the Pacific, reaching Alaska, Hawaii and Chile. In Chile, some 11,000 miles (17,000 km) distant, the tsunami was 6.6 feet (2 meters) high when they reached the shore.

The surge of water carried tons of debris out to sea as it receded. Japanese docks and ships, and countless household items, have arrived on U.S. and Canadian shores in the ensuing years. The U.S. Coast Guard fired on and sank the derelict boat 164-foot Ryou-Un Maru in 2012 in the Gulf of Alaska. The ship started its journey in Hokkaido. 

Amazing facts

Here are some of the amazing facts about the Japan earthquake and tsunami.

• The earthquake shifted Earth on its axis of rotation by redistributing mass, like putting a dent in a wobbling top. The temblor also shortened the length of day by about a microsecond.
• More than 1,000 aftershocks have hit Japan since the earthquake, the largest a magnitude 7.9.
• About 250 miles (400 km) of Japan's northern Honshu coastline dropped by 2 feet (0.6 meters).
• The jolt moved Japan's main island of Honshu eastward by 8 feet (2.4 meters).
• The Pacific Plate slid westward near the epicenter by 79 feet (24 m).
• In Antarctica, the seismic waves from the earthquake sped up the Whillans Ice Stream, jolting it by about 1.5 feet (0.5 meters).
• The tsunami broke icebergs off the Sulzberger Ice Shelf in Antarctica.
• As the tsunami crossed the Pacific Ocean, a 5-foot high (1.5 m) high wave killed more than 110,000 nesting seabirds at the Midway Atoll National Wildlife Refuge.
• In Norway, water in some fjords pointing northeast toward Japan (up and over the pole) sloshed back and forth as seismic waves from the earthquake raced through.
• The earthquake produced a low-frequency rumble called infrasound, which traveled into space and was detected by the Goce satellite. LifeScience