U.S. Geologists Explain Science Behind Japanese Earthquake

U.S. Geologists Explain Science Behind Japanese Earthquake

By Lauren Monsen
Staff Writer

Washington - A massive earthquake measured at magnitude 8.9 struck northeast Japan March 11, the most powerful quake in that country's recorded history, according to the U.S. Geological Survey.

The earthquake triggered a tsunami on Japan's east coast, killing at least 15 people and sweeping away houses, cars and boats. Because the earthquake's hypocenter, or rupture point, was 24.4 kilometers (15.2 miles) deep, it qualifies as a shallow earthquake, which is the most hazardous kind, according to USGS seismologist Juan Cantavella.

"The closer an earthquake is to the epicenter - the surface, where people are - the more dangerous it is," Cantavella explained. "As a general rule, if the initial rupture point is less than 100 kilometers, it's a shallow quake. An intermediate quake would be between 100 to 300 kilometers, and anything below that is considered a deep earthquake. The deepest [earthquakes] are about 600 kilometers or so" below the earth's surface.

Japan's earthquake was followed by at least 19 aftershocks, affecting dozens of cities and villages along the country's eastern shoreline. Even Japan's capital city, Tokyo, hundreds of miles from the quake's epicenter, experienced violent tremors of magnitude 6. The quake has caused significant damage to energy infrastructure, although nuclear facilities are said to be unaffected.

Earthquakes have only been recorded in Japan since the 1800s, but the next most powerful quake occurred there in 1896, measuring 8.5 on the Richter scale. That earthquake produced about 27,000 fatalities.

U.S. Ambassador to Japan John Roos said U.S. military forces stationed in Japan are ready to work with Japanese authorities to deal with the earthquake. All U.S. Navy vessels deployed in Japan, including those at Yokosuka, Kanagawa Prefecture, and Sasebo, Nagasaki Prefecture, were safe, and no injuries to any 7th Fleet personnel or damage to the fleet's assets have been reported, the Navy said.

"We will continue to monitor the situation and coordinate with the municipal, prefectural and national governments in the event we are requested to provide assistance by the Japanese government," the Navy said in a statement.

The March 11 earthquake follows on the heels of two other deadly earthquakes in the Pacific Rim. On February 22, New Zealand suffered an earthquake measured at magnitude 6.3, and on March 10, a 5.8-magnitude earthquake occurred in China. Despite the short intervals between each quake, "it's very unlikely" that these events are related in any way, USGS seismologist Robert Williams said.

"The earth is always sending out pretty big earthquakes fairly consistently," Williams said. "But because of the distances between these earthquakes, they're almost certainly not related." He pointed out, however, that earthquakes do trigger lesser quakes, or aftershocks, in surrounding areas, as the Japanese earthquake demonstrates. The aftershocks can be lethal as well.

Japan's earthquake prompted tsunami warnings for the entire Pacific area, including South America, the U.S. West Coast, Canada and Alaska.

Since the mammoth Indian Ocean tsunami that struck in December 2004, killing more than 230,000 people in 14 countries, an increasingly sophisticated global system has been created to detect and respond to earthquakes and tsunamis. The UNESCO Intergovernmental Oceanographic Commission provides oversight and coordination - and many nations contribute technical and financial help - to support seismic and tsunami warning systems in the Indian Ocean, the northeast Atlantic and Mediterranean, and the Pacific.

ENDS

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