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Check out this article from the Wall Street Journal about the recent Earthquake in Japan.
Earth's Energy Unleashed as Tectonic Plates Shift
![[TSUNAMI]](http://si.wsj.net/public/resources/images/WO-AE751_TSUNAM_G_20110311201009.jpg)
Reuters The tsunami washes inland Friday in coastal areas of Iwanuma, Miyagi prefecture, in northeastern Japan.
Even in Japan's turbulent seismic history, the 8.9-magnitude earthquake that struck Friday was one for the record books.
The quake—the fifth-largest recorded since 1900 and the biggest to hit Japan in three centuries—released almost 1,000 times the energy released in the Haiti quake a year ago. Friday's quake also triggered a tsunami that traversed the planet, all the way to the shores of California.
Seismologists at the Lamont-Doherty Earth Observatory in Palisades, N.Y., talk with WSJ's Christina Tsuei about the science behind Japan's devastating earthquake.
Tsunami-causing quakes usually occur where shards of the earth's crust—tectonic plates—meet. Magma rises from deep inside the Earth, causing the plates to move. They slide past each other but sometimes get stuck. When they jerk forward again, they can trigger a quake.
Friday's quake occurred where the Pacific plate, moving at a speed of about three inches a year, slides under the Eurasian plate. The last big quake there occurred in 1933, causing 3,000 deaths. Since then, the plates have been trying to move past each other, but have been jammed in place.
On Friday, the accumulated strain overcame the strength of the rocks deep beneath the sea some 80 miles offshore. "The rocks cracked under the pressure," causing the plates to jerk forward again, said John Elliott, an earthquake geophysicist at the Centre for the Observation and Modelling of Earthquakes and Tectonics at Oxford University in England.
The jerking motion of one plate moving under the other caused a massive uplift of the seafloor, convulsing an area almost 200 miles long and 50 miles wide.
"It's hard to even imagine just how much water was displaced," said Lynda Lastowka, seismologist at the United States Geological Survey.
The resulting 30-foot-tall tsunami slammed into Japan's northern coast and swept away people cars, boats and buildings.
A 30-foot-high tsunami brought catastrophe to cities and towns up and down 1,300 miles of Japan's northern coastline. WSJ's Jason Bellini maps out the city-by-city devastation.
The tsunami traveled across the Pacific at about 550 miles per hour, or the speed of a jet plane. Its undulations likely passed unnoticed on most ships, because the crests tend to be less than three feet tall and are hundreds of miles apart.
A system known as Deep Ocean Assessment and Reporting of Tsunamis, or DART, picked up the signals and allowed officials to issue tsunami warnings reaching across the Pacific Ocean.
DART, developed by the U.S. National Oceanic and Atmospheric Administration, consists of spheres moored to the deep ocean floor that use pressure gauges to measure the variation in sea levels. Data from a tsunami wave passing overhead are sent to a buoy on the sea surface, which zaps the information via satellite to monitoring stations in Hawaii and elsewhere.
The awesome force of a tsunami only becomes apparent in shallow water. As it approaches the coast, the wave slows down to about 20 to 30 miles an hour. By then, all its energy is packed into much less depth, which can increase the wave's height dramatically.
Though Friday's tsunami caused tremendous devastation in northern Japan, its impact elsewhere appears to have been modest. Waves as tall as 5.7 feet were reported at a harbor in Hawaii, while some parts of central California saw waves as high as 6.2 feet, according the USGS.
The tsunami unleashed by the 2004 Indonesian quake was far more destructive to far-off places than the tsunami generated near Japan. The 2004 temblor was bigger—9.1 magnitude—and released far more energy. In addition, the 2004 wave had to travel only 800 miles before it reached Sri Lanka, one of the hardest-hit countries. By comparison, the Japan tsunami traveled about 3,500 miles to reach Hawaii, which dissipated a good amount of its energy.
