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TOKYO — A powerful earthquake struck western Japan on New Year’s Day, killing dozens of people, destroying homes and triggering fears of greater harm from aftershocks, tsunamis and landslides.
Japan is no stranger to earthquakes. In fact, it’s among the most seismically active countries in the world and the birthplace of seismology, or the study of earthquakes. The study of tsunamis (the word in Japanese means harbor and wave) began here as well.
Japan has regularly grabbed international headlines for earthquake-related damage, most prominently the March 2011 triple disaster of a 9.0-magnitude earthquake, tsunami and nuclear meltdown that led to the worst nuclear disaster since Chernobyl in 1986.
So we asked experts: What makes Japan so prone to earthquakes?
A mosaic of tectonic plates
Earthquakes happen when two tectonic plates butt heads and one slips under the other — releasing a sudden burst of energy.
Japan sits on top of four major tectonic plates, making it one of the places in the world most likely to experience tectonic activity.
“The more plates you have and, more importantly, the more plate boundaries that you have adjacent to or crossing a country like Japan, the more interaction of those plates on which earthquakes occur,” said Robert Butler, professor emeritus of geophysics at the University of Portland and University of Arizona. “So more plate boundaries mean more earthquakes.”
Japan and its surrounding area account for 18 percent of earthquakes in the world because of the active tectonics, said Saeko Kita, seismologist at the International Institute of Seismology and Earthquake Engineering in Ibaraki, Japan.
Japan and the Ring of Fire
Every year, Japan has about 1,500 earthquakes that can be felt by people. In fact, some kind of seismic activity is recorded about once every five minutes.
It’s not unusual for there to be so much earthquake activity along the horseshoe-shaped zone — often referred to as the “Ring of Fire” — along the rim of the Pacific Ocean, with more than 400 active volcanoes. The zone spans from the eastern coast of Australia up to eastern Russia, and down the western coast of North America and along the western coast of Chile.
Japan earthquakes and the Ring of Fire
This is a geologically active area where earthquakes, tsunamis and volcanoes are common. About 80 percent of the world’s largest earthquakes and tsunamis occur in this region, according to the U.S. Geological Survey and the International Tsunami Information Center.
Taiwan and the Philippines sit atop three major tectonic plates and are susceptible to earthquake activity as well, said Lucy Jones, a seismologist who spent more than three decades with the U.S. Geological Survey.
And while Japan is a bigger and more populous country than Taiwan and the Philippines, more attention has been paid to Japan, partly because of a perception that more people are affected by earthquakes, Jones said. Japan’s long history of recording and studying the impact of earthquakes and tsunamis, combined with its extensive disaster preparation, has fueled that perception, she said.
“The reality is that the Philippines and Taiwan have as many [earthquakes] as Japan, but I think part of the perception is because Japan has developed the technology to deal with it,” Jones said.
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The location of the New Year’s earthquake and aftershocks, on the west coast of central Japan, is near an area where several large inland earthquakes have also occurred, experts say.
It was also on the side of the Sea of Japan, or the East Sea. This is different from the majority of major earthquakes and tsunamis in Japan, which are on the eastern, Pacific Ocean side. Still, a few major earthquakes have struck on the western side in recent decades, said Robert Geller, a seismologist and professor emeritus at the University of Tokyo.
“From time to time, there are large quakes under the Sea of Japan. [Large earthquakes in] 1983 and 1993 were the most recent ones till the one that hit two days ago,” Geller said.
There are indications of fluid rising from deep underground in the epicenter of the earthquake, which may have initiated the rupture of the Jan. 1 quake, said Junichi Nakajima, professor in the Department of Earth and Planetary Sciences at the Tokyo Institute of Technology.
The death toll from the New Year’s earthquake in Ishikawa Prefecture has surpassed 62, with more than 100 buildings and about 1,000 homes destroyed.
Japan measures earthquakes by how much the ground shakes, not by the magnitude. The Jan. 1 earthquake was measured at 7 on Japan’s intensity scale, the highest it goes.
Compare that with a century ago, when the Great Kanto Quake — which registered at the equivalent of a 7 or upper 6 on the modern scale — struck the capital, Tokyo, leaving more than 105,000 people dead or missing and about 80,000 homes destroyed. That earthquake led to the establishment of the modern building codes that incorporate the risks of earthquakes.
With every major earthquake, the country has reviewed the damage and updated its building codes, with the last major update in 1981 introducing new standards for earthquake-resistant buildings in the aftermath of a major earthquake in 1978.
In remote and less urbanized parts of Japan, such as Noto Peninsula, where the earthquake struck on Jan. 1, many buildings remain susceptible to damage and collapse because they were built before 1981, said Nobuhito Mori, deputy director of the Disaster Prevention Research Institute at Kyoto University in Japan.
After the 1995 Kobe earthquake, the Japanese government made changes to its disaster response that allowed it to gather information within five minutes of an earthquake, said Geller of the University of Tokyo, and allowed rapid deployment of disaster relief personnel.
Julia Mio Inuma contributed to this report.