A statistical analysis and comparison of historical earthquake and tsunami disasters in Japan and Indonesia

• The average inter-occurrence time between two consecutive tsunamis in Japan is half that of Indonesia.
• The trend of average D&M in Japan exhibits a declining trend, whereas in Indonesia, it shows an increasing trend.
• The occurrences of earthquakes and tsunamis show an increasing trend over time.
• Exponential distribution fits the data of the inter-occurrence, while Poisson distribution fits the data of the D&M.
• Increased knowledge and disaster preparedness need to be enhanced in order to reduce casualties.

This study aims at quantitatively investigating the past trend of natural disasters, focusing upon earthquakes and tsunamis, which occurred in Japan and Indonesia with respect to their occurrences and human casualties; including both deaths and missing people (D&M). We apply mathematical policy analysis techniques in our natural disaster risk analysis and assessment in order to develop policies to mitigate the casualties caused by these natural disasters. First, we review the historical trend of earthquakes and tsunamis related to their occurrences and D&M from 1900 to 2012 to explain their occurrence frequency and forecast the D&M using probabilistic models. We divide the entire period into three time-periods and compare their tendency in both countries. Using about 100 years of data, our study confirms that the Exponential distribution fits the data of inter-occurrence times between two consecutive earthquakes and tsunamis, while the Poisson distribution fits the data of D&M. The average numbers of inter-occurrence times of earthquakes for Japan and Indonesia are 186.23 days and 167.77 days, respectively, whilst those of tsunamis are 273.31 days and 490.71 days, respectively. We find that earthquakes with magnitudes ranging from 6.0 Mw to 7.4 Mw and having epicenters in the mainland cause more casualties, while those with magnitudes 7.5 Mw and above and having epicenters offshore/at sea cause relatively fewer casualties. This implies that mainland earthquakes have higher probability to bring more casualties than the sea earthquakes. In terms of fatalities, earthquakes and tsunamis have caused more deaths in Japan than in Indonesia.