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

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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.