1980 Volume 291 Pages 45-52
In the Miyagiken-oki Earthquakes of February 20 and June 12, 1978, strong motion accelerograms were observed at neighboring three buildings (J.N.R., SUMITOMO-SEIMEI, 77 BANK) in Sendai City. These building are located within radius 300m (see Fig.1), and have almost same soil conditions composed of hard rock (see Fig.2). Seismographs installed in the basement floors of these buildings are set to almost N-S, and E-W direction, and therefore these records can be directly compared in each direction. These records were observed in different types of buildings, consequently in order to eliminate the influence of buildings and to determine the free-surface motions, each building was idealized as a mass-spring mathematical model, in which the spring-dashpot system for the foundation was assumed based on Ground Compliance Theory (refer to literature 6). As a result of this analysis, it was proved that the whole characteristics of acceleration time histories and acceleration response spectra at the basements and the free surface were slightly changed. The characteristics of free surface motions at three points were studied. Maximum velocities obtained by numerical integration were proved to be of the smaller dispersion at three points than the maximum accelerations, so authors paid much attention to velocity time histories, and compared the wave characteris tcs, horizontal orbits, and its cross-correlations. Finally, in both earthquakes, the authors found fairly good similarity of velocity time histories at the neighboring three points.
