Japan lies at the meeting point of four tectonic plates. Massive earthquakes will occur at their boundaries, and it is an unavoidable threat. Above all, massive subduction zone earthquakes repeatedly occur approximately on a 100- to 150-year cycle along the Nankai Trough, which extends from off the coast of Tokai to Hyuga-nada in Kyushu. The earthquakes originating in the Tokai, Tonankai, and Nankai areas have occurred almost simultaneously or sequentially with intervals of several years, causing serious disasters.

In 1707, all the Tokai, Tonankai, and Nankai earthquakes occurred simultaneously. In 1854, the Tokai and Tonankai occurred simultaneously, triggering the occurrence of the Nankai about 30 hours later. The Tonankai occurred in 1944 and the Nankai two years later.

Although we cannot prevent the occurrence of an earthquake, we can minimize the damage. In this project, a number of research institutes worked together to carry out research into the Tokai, Tonankai, and Nankai earthquakes with a focus on the three themes; "search", "predict" and "be prepared". We have researched and observed the crustal structures, conditions, and seismic activities of the Nankai Trough in detail with state-of-the-art observation equipment and predicted what would occur with a high degree of accuracy using a realistic numerical simulation that stands on research results. The prediction about the strong ground motion and tsunamis will be fully utilized as the basis of the preparation for earthquakes; information is shared through regular regional study meetings and others and used in drawing hazard maps and developing recovery/reconstruction plans.

The probability of the occurrence of an earthquake over the next 30 years is 88% (for reference purposes only) in Tokai (some M8.0), about 70% in Tonankai (around M8.1) and about 60% in Nankai (around M8.4), according to the Headquarters for Earthquake Research Promotion. If all these should occur at the same time, the number of deaths is estimated at 323,000 at maximum, according to the Cabinet Office. The earthquakes will come in these areas. But, we will have far less damage than envisioned, if we do research and observation, predict the detailed conditions in the event of an earthquake based on what we have made clear, and take adequate measures according to the prediction.

We study and identify the degree of interrelation between the Tokai, Tonankai, and Nankai earthquakes to realize an earthquake-proof society.