When large-scale earthquake disasters occur, the damage tends to impact elderly people more significantly than younger people. Generally speaking, as people age, they become physically and mentally weaker, and their risk of death increases. The results of previous studies show that the death toll following earthquake disasters was influenced by age and gender of the population of a given disaster area, but that influence has not been quantitatively assessed. In this paper, we evaluate human damage as being a calculation formula based on the age structure of the population of a large-scale earthquake disaster area. We showed the death risk for each age group by quantitatively assessing the distribution of the death rate after having made disaster area population clear. The distribution of the dead is expressed as a formula, using age distribution based on past results. We examined the distributions of the dead for six earthquakes: the 1948 Fukui earthquake, the 1983 Central Sea of Japan earthquake, the 1993 earthquake off the southwest coast of Hokkaido, the 1995 Kobe earthquake, the 2004 Niigata earthquake, and the 2011 Great East Japan Earthquake. We found that the death toll correlates with age in cases of large-scale earthquakes, and the total expected death toll of future earthquakes was calculated using current population data. We applied this formula to the case of a hypothetical Tokyo inland quake.
The death toll of a given earthquake varies according to the type and scale of the earthquake. Various factors influence how the death toll is determined. The formulae for predicting death toll based on either type or scale have been proposed by a couple of researchers so far. In this paper, we applied the death toll prediction formula proposed by Yutaka Ohta in 1983.
The human damage data in the event of a large-scale earthquake disaster is provided as follows.
(1) There is an obvious correlation between the age structure of the disaster area population and the death toll. The incidence rate of the dead represents the tendency of the death toll in each age group.
(2) We precisely evaluated the death risk quantitatively, independently expressing the numbers in each age group.
(3) The death risk differs depending on the type of quake. Two types of damage are expressed in the following formulas:
Earthquake with heavy structural damage:
αD=3.511×10-11X6-1.323×10-8X5+2.152×10-6X4-1.36×10-4X3+3.79×10-3X2-4.603×10-2X+0.741
Earthquake with heavy tsunami damage:
αD=2.424×10-10X6-5.744×10-8X5+4.848×10-6X4-1.75×10-4X3+3.177×10-3X2-2.884×10-2X+0.4
(4) Based on our trial calculation of the potential death toll of a future Tokyo inland quake, it is necessary to consider changes to the age structure of the population in Tokyo.
Based upon the foregoing, considerations about old, unsafe houses built before 1981 (where elderly people generally live) are necessary to reduce the damage from a future Tokyo inland quake. It will be necessary to carry out detailed examinations focusing on the influence of earthquake death toll on age and gender using this formula.
