This isn't likely to happen on the East Coast, but it could. This is an aerial view of damage to Sukuiso, Japan, a week after the earthquake and subsequent tsunami devastated the area in March, 2011.

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 has continued to wash up on North American beaches years later.

In Japan, residents are still recovering from the disaster. As of February 2017, there were still about 150,000 evacuees who lost their homes; 50,000 of them were still living in temporary housing, Japan's Reconstruction Agency said.

More than 120,000 buildings were destroyed, 278,000 were half-destroyed and 726,000 were partially destroyed, the agency said. The direct financial damage from the disaster is estimated to be about $199 billion dollars (about 16.9 trillion yen), according to the Japanese government. The total economic cost could reach up to $235 billion, the World Bank estimated, making it the costliest natural disaster in world history.

This map shows the travel times of the tsunami generated by the Honshu earthquake on March 11, 2011. (Image credit: NOAA/NWS)

Earthquake a surprise

The unexpected disaster was neither the largest nor the 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 forecast 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.

"For big earthquakes, the tsunami is going to be the big destructive factor," said Vasily Titov, director of the National Oceanic and Atmospheric Administration's Center for Tsunami Research in Seattle, Washington. "But if the nation is prepared, warning and education definitely saves lives. Compare the human lives lost in Sumatra and Japan. It's about 10 times less."

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 are rough and stick together, building up energy that is released as 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 March 11 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 15 miles (24 km) below the surface. The shaking lasted about six minutes. [Infographic: How Japan's 2011 Earthquake Happened]

Scientists drilled into the subduction zone soon after the earthquake and discovered a thin, slippery clay layer lining the fault. The researchers think that this clay layer allowed the two plates to slide an incredible distance, some 164 feet (50 meters), facilitating the enormous earthquake and tsunami.

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 and tsunami warnings on their cellphones.

Deaths

The number of confirmed deaths is 15,894 as of June 10, 2016, according to the reconstruction agency. More than 2,500 people are still reported missing.

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. The electrical power and backup generators were overwhelmed by the tsunami, and the plant lost its cooling capabilities.

"Fukushima was created by the tsunami. The earthquake was not a factor," Titov said. "Fukushima was designed for a tsunami smaller than the one we saw."

Very low levels of radioactive chemicals that leaked from Fukushima have been detected along the North American coast offshore Canada and California. Trace amounts of cesium-134 and cesium-137 (radioactive isotopes) were found in seawater collected in 2014 and 2015.

Houses above the inundation zone in this Japanese village survived intact, while everything below was destroyed by the 2011 tsunami. (Image credit: Patrick Corcoran, Oregon State University)

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 Japanese government study published in August 2011. 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.

"The tsunami itself died out a long time ago, but the effects in Japan will be there for decades," Titov told Live Science.

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, according to the Pacific Tsunami Warning Center. [Related: Weird Earth Movement After Japan Earthquake Finally Explained]

The surge of water carried an estimated 5 million tons of debris out to sea, the National Oceanic and Atmospheric Agency has reported. 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 spinning top. The temblor also shortened the length of a day by about a microsecond.

More than 5,000 aftershocks hit Japan in the year after 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), according to the U.S. Geological Survey.

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 fjords pointing toward Japan 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.

Buildings destroyed by the tsunami released thousands of tons of ozone-destroying chemicals and greenhouse gases into the air.

Additional resources

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