1946 Nankai earthquake ( 昭和南海地震 Shōwa Nankai jishin ) was a great earthquake in Nankaidō , Japan . It occurred on December 21 , 1946 , at 04:19 JST ( December 20 , 19:19 UTC ) . The earthquake measured between 8.1 and 8.4 on the moment magnitude scale , and was felt from Northern Honshū to Kyūshū . It occurred almost two years after the 1944 Tōnankai earthquake , which ruptured the adjacent part of the Nankai megathrust
1944 Tōnankai earthquake
1944 Tōnankai earthquake
1946 Nankai earthquake