【1】 What Causes Earthquakes?
   The surface of the earth is comprised of massive rock plates that are tens of kilometers thick. These plates move at an extremely slow rate of several centimeters per year.
   In the middle of Tosa Bay, the Philippine Sea Plate is slowly being pushed beneath the Eurasian Plate. Over time, stress builds up along the boundary between these two plates. When this stress builds to a point that can no longer be withstood, the plate that was pulled under will slip back up to its original position, resulting in the Nankai Earthquake.
   When this occurs, all areas in Kochi Prefecture will experience very serious tremors. Furthermore, because the sea floor will rise and fall, a Tsunami will also occur.