The Probabilistic Seismic Hazard Maps for Japan (PSHMJ) have been criticized after the 2011 Tohoku earthquake. For example, Geller (2011) complained that recent damaging earthquakes occurred in places assigned a relatively low probability in the 2010 PSHMJ map of Intensity 6- or greater in 30 years. However, Miyazawa and Mori (2009, 2010) constructed maximum seismic intensity maps using recorded historical data for the past 500 years, and found that they agreed with the 2008 PSHMJ map of 10% in 50 years, which is equivalent to a hazard map of probable seismic intensity for a 475-year return period if we assume a Poisson distribution. We here explore a reason for the difference of the above two, using seismic intensities actually observed by the Japan Meteorological Agency and others.

In Japan, we have seismic intensities actually observed in 1890 and later, and Miyakoshi et al. (2016) provided seismic intensity hazard curves at every grid point not only for the PSHMJ map of 2016 but also for those of 1890, 1920, 1950, and 1980. If we assume a Poisson distribution for seismic intensities like Miyazawa and Mori (2009), a PSHMJ map of 64% in 30 years is equivalent to a hazard map of probable seismic intensity for a 30-year return period. Therefore, we construct maximum seismic intensity maps using the observed intensities in 30 years from 1890, 1920, 1950, or 1980. We also construct PSHMJ maps of 1890, 1920, 1950, or 1980 using the intensities estimated for a probability of 64% in 30 years. We then compare the observed and estimated intensities at a same site, finding that the correlation between them is positive but very weak. This weakness may correspond to Geller’s (2011) criticism, probably because a period of 30 years is too short for a large intensity to be observed. If we adopt a period of 100 years, the correlation is certainly improved, approaching to the result of Miyazawa and Mori (2009) for a period of 500 years.