Abstract
It is one of the most important problems in earthquake engineering to predict the intensity of future earthquakes from the past available earthquake recording data, as precise earthquake forecasting is difficult in the present stage. The expectancy of maximum earthquake motions in a certain place may be defined by the seismic activity on the base rock and the ground characteristics. In order to clarify this more reliably, it is necessary to investigate the regional distribution or variation of the seismic activity and the characteristics of soil-layers. The expectancy of maximum earthquake motions based on the seismic activity on the base rock by means of Kanai's Formula and Gumbel's Second Asymtotic Distribution was reported in Apr., 1978. This paper deals with the regional distribution of the characteristics of soil-layers in the range of long period (6.0≧T≧2.0sec.) reflecting the deep ground characteristics of fairly large area, using seismic data of strong motion seismographs published by Japan Meteorological Agency. This paper is summarized as follows, (1) The regional distributions of the magnification of soil-layers in the range of long period reflecting the deep ground characteristics are showed in Fig. 6 (a)〜(b) and Appendix II. As a result, the areas where the magnification factor is considered to be high are generally as follows, i) the coast on the Japan Sea in the Tohoku district from the Hokkaido district, ii) the southern area of the Kwanto district from the area of the Kinki district, iii) the southwestern area of the Shikoku district from the Kyushu district. However the above tendency of the regional distribution varies in detail according to the period components of earthquake motions. (2) The relations between the magnitude (M) and the predominant period (T) of earthquake motion (log T=aM+b), and between the maximum amplitude of the vertical and the horizontal components (R_m) are examined. And the regional distributions of coefficients a, b and R_m are indicated in Figs. 11 and Appendix I. From these figures, it is pointedout that the coefficients a, b and R_m are influenced by the soil characteristics as well as the regional distribution of the magnification factor. 3) It is proposed that the expectancy of maximum earthquake motions on the structural base rack with V_s=0.6〜0.8km/sec. can be expressed for the long period (6≥T≤2sec.) as the product of the following three factors i) the expectancy of maximum earthquake motions based on seismic activity on the seismic base rock with V_s=2〜3km/sec., ii) the magnification factor of the standard ground characteristics, and iii) the regional distribution of the quake degree relative to the standard ground. The procedure of estimation in Tokyo is schematically described in Fig. 17. It is necessary to take consideration that the aspect of the final regional distribution of the expectancy of earthquake motions is different from that based on the seismic base rock in following areas, the southern part of the Kinki district, the area from the south-western part of the Kyushu district to the west-southern port of the Shikoku district, the coast area on the Japan Sea in the Tohouk district and so on. In addition, the effects of the soil characteristics in the short period rarge (T≦1.0〜2.0sec.) reflecting the shallow ground characteristics on a small area or the concepiton of the soil profile types should be introduced from the practical point of view.
