User:Correctemundo/Tokai earthquakes

The Tokai earthquakes are earthquakes that have occured regularly with an interval of 100 to 150 years in the Tōkai region of Japan.

The whole country of Japan affected by earthquakes, but the most dangerous area of Japan is the coastal area just southwest of Tokyo on the island Honshū. In this area the Philippine plate is moving under the Eurasian plate. Japanese geologists have studied historical earthquake records, and mapped out segments of the area that seem to be affected repeatedly on a regular basis. This coastal area southwest of Tokyo, around Suruga Bay, is called the Tokai segment.

Last time a major earthquake affected the Tokai region was in 1854. Given the historic regularity the next earthquake is expected in the near futute. The Japanese government is taking the Tokai earthquakes seriously and has charged the Japan Meteorological Agency with the job of predicting the next one. They have a dense array of instruments placed to accumulate a continuous stream of data related to seismicity, strain, crustal expansion, tilt, tidal variations, ground water fluctuations and other variables. They are watching for an anomaly in this data which might precede the next major Tokai earthquake.

The anticipated Tokai earthquake is visualized in scenarios used by emergency planners. They need to create plans for an event that will likely thousands of deaths and injuries, and a million damaged buildings. It is expected to be at least magnitude 8 and large areas will be shaken at intensity 7, the highest level in the Japanese intensity scale. The magnitude is high so large damages are expected. But there is a lot of preparations in place.

Historical relation to other major earthquakes
The pattern of historical seismicity reveals that the megathrust surface is segmented, with five separate zones of rupturing identified, conventionally labelled A–E, from west to east. Earthquakes involving the A+B segments are generally referred to as Nankai (literally South Sea) earthquakes, C+D Tonankai (literally Southeast Sea) earthquakes and E Tokai (literally East Sea) earthquakes. The earthquake repeat intervals are generally in the range 90–200 years.

On all but one occasion, rupture of segment C (±­D ±E) has been followed by rupture of segments A+B within a few years. This behaviour has been reproduced by modelling the viscoelastic response of the megathrust fault plane with lateral variations in both convergence rate and frictional properties.