Honshu Island, located southwest of Tokyo, has been considered the most earthquake-prone region in Japan. It is here that Japanese geologists found regular and repeated movements of earth’s plates causing them to rapture.
What are the earth’s plates? The earth is composed of layers: inner and outer core, lower and upper mantle, transition region and the crust. The outermost layer consists of the crustal plates which are broken into huge and thick platelets that drift on top of the underlying soft mantle. Over time these plates move all over the globe in a horizontal and vertical motion. They also change in size or crushed together or pushed back down into the mantle.
What is the Tokai Earthquake? Beneath the coast within the Suruga Bay area, in front of Mount Fuji and southwest of Tokyo is the Tokai segment. It is in this region that most of the earth’s plates have been breaking into pieces. Historical records show that Tokai segment ruptured in 1498, 1605, 1707 and 1854. It is for this reason that in 1978 government officials passed a legislation declaring the Tokai segment as an “area under intensified measures against earthquake disaster”, also known as the Large-Scale Earthquake Countermeasures Act.
Japan has been preparing for the 21st century great Tokai Earthquake to happen. The 8.8-magnitude quake that rocked Honshu Island in March 11,2011 happened in a different fault line. This is not the Tokai Earthquake. The country is still at risk of being struck by a more powerful earthquake when the Tokai segment ruptures again. A 14-page guidebook has been prepared by the government to educate them on what to do in the event of the great quake.