By The Economist
The giant tectonic plates which make up Earth’s outermost layer are always on the move, sliding past and colliding with each other. This creates plenty of seismic activity, especially in the area around the Pacific Ocean known as the “Ring of Fire”, which accounts for some 90% of the world’s earthquakes. On April 14th a magnitude 6.2 tremor shook Kumamoto prefecture on the southern Japanese island of Kyushu. Then, in the early hours of the morning on April 16th, a magnitude 7.0 quake struck the same area. On the same day, on the opposite side of the ring, a coastal region of Manabí and Esmeraldas provinces in Ecuador was shaken violently by a magnitude 7.8 quake—15 times stronger in terms of the energy released than the second Japanese quake. In Japan more than 40 people died; in Ecuador the death toll is expected to exceed 525.
The greatest risk posed by earthquakes on land comes from buildings collapsing. Whether or not they fall down depends both on circumstance and on how they are built. This was evident in both disasters. In Ecuador, traditional homes made largely from bamboo withstood the quake better because of their flexibility. The more affluent, living in buildings made of concrete, were less lucky as walls, floors and roofs collapsed (as pictured above). In Mashiki, a town hard hit by the two Japanese earthquakes, dozens of traditional wooden homes collapsed, along with the community’s Buddhist temple and Shinto shrine. But among them stands a more recent house that remains unscathed, rather like a gleaming tooth among otherwise rotten gums. Inside, recounts its relieved elderly owner, her cups and saucers were flung around but the house stood firm.
Last one standing
That solitary house underlines one of the most successful ways to protect against seismic activity. The most important part of Japan’s approach remains its stringent building code, says Naoshi Hirata of the Earthquake Research Institute (ERI) at the University of Tokyo.
For decades Japan has tightened its construction codes—by now the world’s strictest—and supported other innovations in quake-proofing construction methods. All buildings constructed after 1981 had to be sturdy enough to withstand collapse in an earthquake with an intensity of “upper 6” or higher on the scale used by the Japan Meteorological Agency (which measures shaking at individual points whereas magnitude measures the size of an earthquake). The regulations were strengthened again after the quake that hit Kobe in 1995, which had a magnitude of 6.8.
Those building regulations have sharply reduced both the rate of collapsed structures and the risk of fires spreading. When the March 2011 earthquake struck off the Pacific coast of Tohoku it was the ensuing tsunami that wrecked the coastal region, setting off a nuclear meltdown at the Fukushima Dai-ichi nuclear-power plant. Most newer buildings withstood the shaking, which was somewhat attenuated by the time the seismic waves reached land.
Ecuador introduced stricter seismic regulations of its own after the Haiti earthquake in 2010. But there are problems. Hugo Yepes, a geophysicist at the National Polytechnical University in Quito, complains that builders and developers have been largely ignoring them and that local officials have effectively “legalised” informal new neighbourhoods without insisting on anti-seismic standards. When visiting the area, Rafael Correa, Ecuador’s president, said building standards had to be applied with greater rigour to avoid a similar scale of destruction in the future.
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