The Japanese government has adopted two separate disaster plan since 2014. One addresses earthquakes of a magnitude-8 quake directly under Tokyo’s main 23 wards, and the other is originating in the Nankai Trough, which extends for hundreds of kilometers parallel with the Japanese coast. This has triggered six of at least 7.9 in magnitude since 1600.
A report compiled by the Central Disaster Management Council predicts the volatile Nankai Trough could trigger a triple-earthquake of a magnitude-9 combined with a massive tsunami as much as 30 meters high and could kill 320,000 people. The Nankai Trough extends for hundreds of kilometers parallel with the Japanese coast, off heavily populated area and the industrialized zone that runs south of Tokyo through Nagoya, Osaka, Kobe and Hiroshima.
A government report announced last year said that a large-scale and long lasting earthquake originating in the Nankai Trough would likely cause skyscrapers in Tokyo, Nagoya and Osaka areas to sway violently.
In March 2011, during the Great East Japan Earthquake, the 256-meter-high, 55-story Sakishima Building of the Osaka Prefectural Government, located some 770 km from the seismic center, swung up to 2.7 meters for roughly 10 minutes, damaging interior material and fire doors at some 360 spots and halting all elevators. There were reports that people in the building felt as if they were aboard a rolling ship. In Tokyo, elevator operations stopped in many high-rise buildings, trapping people inside.
The government report, the first study of its kind, estimates the effects of the phenomenon, which is known as ‘long-period ground motions’, to tall buildings. Slow-shaking quake motions of this kind can damage skyscrapers even if they are located far from the epicenter. (Floro Mercene)