The Nankai earthquakes are major megathrust earthquakes that affect the Nankaidō region of Japan, west of the Tōnankai region and Tōkai region, and are caused by ruptures in the Nankai zone of the Nankai megathrust, specifically segments A and/or B. They occur with a return period of 100 to 200 years, and there is a high probability of one in the 21st century, as the most recent was the 1946 Nankaidō earthquake. Wikipedia