Terremoto e maremoto del Tohoku del 2011

Article

August 19, 2022

The 2011 Tōhoku earthquake (東北 地方 太平洋 沖 地震 Tōhoku chihō taiheiyō-oki jishin ?, "high seas earthquake of the Tōhoku region and the Pacific Ocean"), occurred on March 11, 2011 off the coast of the region of Tōhoku, in northern Japan, at 14:46 local time at a depth of 30 kilometers. The earthquake, of magnitude 8.9-9.0 (according to the USGS), with its epicenter at sea and subsequent tsunami, is the most powerful ever measured in Japan and the fourth worldwide. The earthquake and subsequent tsunami were the cause of the disaster at the Fukushima Dai-ichi nuclear power plant, destroying the emergency generators that powered the cooling systems of three of the plant's reactors.

The earthquake

The earthquake occurred in Miyagi prefecture. The area at the epicenter shook for about 6 minutes, reaching a moment magnitude of 9.0. On the mainland, about 100 km from the epicenter, a maximum seismic shaking value (Modified Mercalli Intensity), corresponding to the ninth degree, was detected. Ground acceleration reached peaks of 2.99 g. Further tremors followed after the initial one at 14:46: one of magnitude 7.0 at 15:06, one of magnitude 7.4 at 15:15 and one of magnitude 7.2 at 15:26, and they were beyond forty tremors with a magnitude greater than 5.0 that took place in the hours following the initial tremor. Many parts of the city of Tokyo were temporarily without electricity. At dawn on March 13 (5:00 local time) there were other shocks of 6.8 and 6.0 in the north-east of the country. On March 14, another great shock of magnitude 6.2 occurs also in Tokyo. On March 15, another quake of the same magnitude occurred 120 kilometers southwest of Tokyo, near Fuji with its epicenter in Shizuoka. On March 16, a 6.0 quake shook Chiba prefecture, on the eastern outskirts of Tokyo. On March 17, state television NHK announced that a new quake of magnitude 5.8 occurred just outside Tokyo, with its epicenter off the coast of Ibaraki prefecture, north of the capital, with the current death toll of 15,704. (most of the casualties and damage were caused by the tsunami) the death toll of the 1995 Kobe earthquake in which 6,434 people died has been exceeded; to help the relatives of the victims to overcome the mourning, the telephone of the wind was built.

The tsunami

Following the tremors, a tsunami was generated with waves over 10 meters high which reached a speed of about 750 km / h. Many countries, including New Zealand, Australia, Russia, Guam, the Philippines, Indonesia, Papua New Guinea, Nauru, Hawaii, the Northern Mariana Islands and Taiwan have, as a result, declared the alert. tsunami. In Japan, the alert was immediately raised to the maximum level. The Japanese coasts most affected by the anomalous waves were that of the prefecture of Iwate, where the highest wave was recorded, which hit near the city of Miyako, which reached the extraordinary height of 40.5 meters, and that of the prefecture of Miyagi, which suffered the most damage, with cars, buildings, ships and trains engulfed by the waves. Mean sea level measurements taken at Cape Roberts station in Antarctica indicate that the oscillations on the sea surface of the wave train following the arrival of the tsunami wave took at least 72 hours to reduce to the level of the oscillations. observable during local storms. The tsunami also reached the Mediterranean Sea, passing through the Strait of Gibraltar. The satellite images showed that the fatigue, induced by these oscillations, on the mass of ice of the Sulzberger ice shelf that flows into the ocean, caused the breaking and detachment from it of two gros