Fig. 2
From: A short history of Japanese historical seismology: past and the present
Number of historical earthquakes listed in each paper. 1951 w/epi and 2013 w/epi show number of earthquakes of which epicenters were estimated in Kawasumi (1951) and Usami et al. (2013), respectively. Each number shows number of events of ancient [416 ad- 1184], medieval [1185–1585], and early modern [1586–1872] periods, respectively. Politically, early modern period of Japan ended in 1868. However, 1872 is usually used as the last year of historical earthquakes in Japan, because we need the conversion of the lunar calendar to Gregorian calendar by this year. The Meiji government switched to the solar calendar from the lunar calendar in the beginning of 1873