Inferred displacements, velocities and rotations of a long rigid foundation located at el centro differential array site during the 1979 imperial valley, california, earthquake

Abstract

AbstractDigitally recorded acceleration time histories of the 1979 Imperial Valley earthquake by the five elements of the El Centro Differential Array are used to estimate the induced torsional and rocking vibrations of long structures in the near field of strong earthquakes. The underlying assumptions in these estimates are high rigidity of the foundation relative to the surrounding soil and its negligible mass. Based on these analyses, the peak rotation amplitude of an 18 m long foundation within 5 km of the fault is approximately 1 × 10−3 rad, or nearly 0·06 degrees, and decreases rapidly for larger foundation dimensions for either the rocking or torsional mode. The strongest impulses of rotations coincide with arrival of the S phase. This paper examines the sensitivity of the resulting peak displacement and particle velocity amplitudes to the foundation dimension. It is inferred that the base averaging effects of displacement and velocity fields at frequencies contributing to peak values (f < 1 Hz) are negligibly small. Rocking and torsional amplitudes for the specific site and geometry considered here show a tendency to reduce with the increase of foundation dimensions.