GeologyRocks

Thousands of people in residents along Japan's eastern coast fled to higher ground after an 8.2 magnitude earthquake triggered tsunami warnings Saturday in parts of the Pacific region, including Hawaii and Alaska.

The warnings, which were lifted nine hours after the quake, rattled coastal residents more than two years after giant waves spawned by an Indian Ocean earthquake killed at least 230,000.

But the largest wave reported by late Saturday was a 16-inch tidal surge along the shores of Chichi-jima, a Pacific island 620 miles south of Tokyo, more than three hours after the quake.

Earlier, a tidal swell of about 4 inches was recorded in Japan's northeastern coastal town of Nemuro, and a higher tide also was observed in other coastal towns, including Kushiro, Abashiri and Otaru, Japan´s Meteorological Agency said.

The quake struck around 1:24 p.m. local time about 310 miles east of Etorofu, the largest of a disputed four-island chain known as the Northern Territories in Japan and the Kuril islands in Russia.

The Japanese agency initially estimated the magnitude as 8.3 but later reduced that to 8.2, the same strength recorded by the U.S. Geological Survey. The quake struck 19 miles below the seabed, the agency said.

There were no immediate reports of injuries or damage from the quake, but the agency warned that higher than usual waves could hit the northeastern coast of Japan's main island of Hokkaido.

Hokkaido officials responded by issuing evacuation orders to 85,000 people in 22 coastal towns.

Disaster prevention official Haruyuki Komachi said thousands of people heeded the orders and gathered at community centers. Police closed off roads to the coast and train operators suspended some services as a precaution.

The warnings were later downgraded to advisories, then canceled them altogether on the northwestern coast of Hokkaido, leading some municipalities to lift evacuation orders. Advisories in other parts of Hokkaido and towns facing the Pacific coast were still in effect late Saturday.

'The tidal change so far seems rather small, but a bigger one may come hours later,' Komachi said. 'So we have to stay vigilant into the night in case a second or a third ones come in bigger waves.'

A tsunami warning also was issued for Alaska's western Aleutian islands, and a tsunami watch was issued for Hawaii. Both were later canceled, but not before dozens of people sought refuge in underground shelters on two Aleutian islands.

The Philippine Institute of Volcanology and Seismology advised residents along that nation's eastern seaboard to observe changes in the sea level. About 4,000 people in the northern province of Isabela were evacuated.

Tsunami warnings are issued due to the imminent threat of a tsunami. Tsunami watches are issued as an advance alert to areas that could be impacted by a tsunami.

Temblors of magnitude 7 are generally classified as major earthquakes, capable of widespread, heavy damage.

The Japanese meteorological agency also issued warnings last November following a magnitude 7.9 quake in a similar area, but most areas saw waves of only about 7.8 inches.

Seismologists, however, warned that this time the quake was stronger and cautioned residents to remain vigilant.

Tokyo University seismologist Yoshinobu Tsuji warned that high waves may still hit the region, hours after a tsunami warning. 'I urge everyone to stay alert,' he said.

On Dec. 26, 2004, a magnitude-9.0 earthquake off Indonesia's Sumatra island unleashed giant waves that fanned out across the Indian Ocean at jetliner speeds, leaving at least 230,000 dead and millions of homeless in its wake.

Source:http://www.topix.net/content/ap/3388957650092264638406924110761023768102?threadid=D6HDI8SR0PC7C91B