The magnitude 8.8 earthquake that struck Chile on Saturday prompted the Japanese Meteorological Agency to issue “major tsunami” alerts. The quake killed more than 700 people in the South American country. Of the estimated 350 people who died in the seaside resort of Constitucion, it is thought many were killed by the impact of a tsunami.
In Japan, according to Kyodo News, evacuation orders were issued to some 522,000 people from nearly 200,000 households in 10 prefectures. Waves reaching heights of 20 cm to 120 cm hit various parts of the nation’s Pacific coast. Although no deaths were reported, the aquaculture industry, especially in the Sanriku coast in the Tohoku region, suffered great damage. The experience is a strong reminder of Japan’s tsunami vulnerability.
A tsunami, unlike ordinary waves, is not generated by the wind or tide. In an underwater earthquake, the ocean floor shifts upward or downward along a fault that might measure anything from several kilometers to several hundred. Water around the fault is displaced at speeds approaching that of a jet aircraft, building into a tsunami. The tsunami gradually slows as it nears land, but can be moving as quickly as 30 kph when it breaks the shoreline. If one has not evacuated by the time a tsunami comes into sight, it is too late.
Even a minor tsunami posesses fearsome power. A 50 cm tsunami exerts a force of some 200 kg against whatever or whomever it hits, an impact that could easily be fatal.
The “major tsunami” warnings issued Sunday morning were the first since 1993, when a major quake occurred southwest of Hokkaido. Four to five minutes after that quake occurred, Okujiri Island, in the Sea of Japan off Hokkaido, was struck by tsunami measuring up to 30 meters high, killing some 200 people.
According to the government, many people did not follow the evacuation orders issued Sunday. Alarmingly, evacuation orders were not even issued to some 1,300 residents of two at-risk districts in Mutsu, Aomori Prefecture. In January 2007, following a quake with a magnitude of around 8 in the Kuril Islands, only 8.7 percent of residents followed evacuation orders. All are ominous signs.
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