Intensity of Earthquake Ground Motion for Seismic Design of Buildings

The recent philosophies and methods in seismic design of buildings are discussed. In these two or three decades, several kinds of new type buildings have been constructed in Japan, that is, high rise buildings, nuclear power plant structures, base isolated buildings, structures on soft soil ground in so called “Water front” areas, and so on. These social demands of constructions have needed new philosophy and method for seismic design. On the other hand, the recent earthquake events occurred in the world, for instance, the 1968 Tokachi-oki earthquake, the 1979 Imperial Valley earthquake, the 1985 Michoacan earthquake and others, showed us important information. The actual situations of building damage and the observed data by strong motion seismographs have showed clearly that the characteristics of earthquake ground motion are greatly effected due to earthquake source processes, seismic wave propagation from source to site, deep subsurface structure in the concerned district and local site conditions. The lessons learned from these recent earthquakes have promoted the developments in the methods of evaluation of intensity of earthquake ground motion to apply the seismic design of buildings. The many kinds of attenuation formulae have been proposed on the basis of the data set of many strong motion accelerograms in the recent destructive earthquakes, and the methods of ground motion simulations have been studied on the theories of physical state on seismic fault, rupture process of seismic source, and wave propagation. Then, the current trends and ideas of evaluation of seismic load, design spectrum or ground motion time histories for response analyses, and new representation of intensity of earthquake ground motion to buildings by “energy spectrum” are discussed in this paper.