Abstract
It is one of the most important problems in earthquake engineering to predict the intensity of future earthquakes statistically from the past available earthquake recording data, as precise earthquake forecast is difficult in the present stage. In the process of the prediction, the selection of the past earthquake recording data and statistical method of analysis are the most important, because the available earthquake recording data are not sufficient. Many researches and investigation have been carried out in this field in Japan. However, there is no research on the prediction of the intensity of future earthquakes based on the theory of extremes developed by E. J. Gumbel. This paper deals with the expected values of the intensity of future earthquakes on base rock mainly. This paper is summarized as follows; (1) Taking into account of the results of reexamination for the data and method of analysis which have been used by many researchers in this field (see Table 1), the following data and method are used; (i) the carthquake data in the vicinity of Japan for the period of 1644〜1972 (329 years), (ii) Dr. Kanai formulate wich give a maximum intensity at the base rock and on the surface of the ground, (iii) Gumbel's Second Asymptotic Distribution in statistics of extremes. Especially about the data before 1926, the treatments with characteristics of velocity at the base rock are applied as follows; (i) the major earthquakes having 2.5cm/sec or more at the base rock are estimated from the destructive earthquakes in the Science Calender, (ii) considering the annual magnitude and energy distribution curves in Figs. 1, 2, 3 and 4, it is aasumed for the small or middle earthquakes less than 2.5cm/sec. at the base rock that the frequency of earthquake occurrence is same as that after 1926 year. (2) The expected maximum velocity at the base rock with standard deviation vs. return period are predicted at the center of Tokyo (35.7°N, 139.8°E) in Fig.6. The expected maximum acceleration, velocity and displacement on the surface of the ground are also listed in Table 4. In addition, the calculated maximum velocity values at the base rock for each year are listed in Tables 2 and 3. (3) Regional distributions of the expected maximum velocity at the base rock are estimated for the return period 50, 100 and 200 years in the vicinity of Japan. As seen in Figs. 7, 8 and 9, the areas where the earthquake danger is considered to be high are generally as follows; (i) the coast area on the Pasific Ocean side from the Hokkaido to Tohoku and Kwanto districts, (ii) the area from west part of the Chubu district to all parts of the Kinki district, (iii) the area from the west part of the Shikoku to the east part of the Kyushu district. (4) For the practical seismic design purpose, the regional seismic zoning map is proposed as reflecting the past seismicity. As seen in Fig.10, Japan is divided into three divisiins by the criterion of seismic activity relatively as follows; A) high seismisity region, B) middle seismisity region and C) low seismisity region.
