COMPOSITION OF SEISMIC LOAD BASED ON THE ALLOWABLE LEVEL OF EARTHQUAKE DAMAGE

在地震灾害的预防中，最重要的是将地震破坏降到最低程度，不产生严重的社会影响。社会影响可以通过报纸上关于地震损失的报道量来估计。对1946 ~ 1995年地震发生后30天内报纸震害报道占总报道的比例进行了调查。报告率随地震发生日的增加而减小，可以用指数函数近似表示。利用这一关系式估计地震灾害的最轻微程度。为了使地震损失达到允许的程度，必须给出日本的可靠地震危险性。利用地震构造基本确定的震源面积，采用概率方法对日本地震危险度图进行了分析。地震发生参数由地震目录的修正震级分布确定。利用这些参数计算了最大加速度和速度的极值分布。100年加速回归期的地震危险度图显示，日本东部地区的地震危险度在300 gal左右，其他地区的地震危险度在100 ~ 200 gal之间。房屋震害总量必须控制在一定的社会允许水平以下，以防止社会恐慌。房屋的破坏程度是由房屋密度的倒数所决定的。提出了结构地震荷载的城市地震因子，以产生房屋的恒定总损伤。这个因素是用一个简单的单自由度结构来检验的。在房屋密度为18到16倍的地区，这个系数增加了100%。

The most important thing in the prevention of earthquake disaster is to reduce the seismic damage to the slightest level which does not yield severe social impact. The social impact can be estimated by the amount of report about seismic damage in the newspaper. The report ratio of seismic damage report to total report in newspapers is surveyed for 30 days after earthquakes from 1946 to 1995. The report ratio decreases with day after earthquake and it can be approximatee by the exponential function. The slightest level of earthquake disaster is estimated using this relation.Reliabale seismic hazard of Japan must be given to estimate seismic damage to be the allowable level of damage. Seismic hazard maps in Japan are analyzed the probabilistic method using the area1, souces which are determined basically from the seismotectonics. Seismic occurrence parameters are determined from the modified magitude ditributions of the earthquake catalogs. The extreme value distributions of the maximum acceleration and the velocity are calculated using these parameters. The seismic hazard map of the 100-year return period of acceleration shows that values in east Japan are almost 300 gals and values in the other region are from 100 to 200 gals.The total number of seismic damage of houses must be decreased below some social allowable level to prevent the social panic. The amount of damage of houses is controlled by the probability of failure which is reciprocal of the concentration of houses. A seismic urban factor of the seismic load of structure is proposed to yield the constant total damage of houses. The factor is examined using a simple single degree of freedom structure. The factor increases by 100% for the region of eighteen times to sixteen times concentrations of houses.