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

SUMMARYDigitally 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 x lo-' 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.

Experimental analysis of seismic torsional ground motion recorded by the LSST‐Lotung array

“…The maximum is reached for short distances. This result was already observed experimentally by Niazi [11] during the 1979 Imperial Valley earthquake and by Loh [12] in the framework of the SMART-1 program. Also, one can observe that the stronger the event, in terms of maximum PGA, the larger the induced torsional amplitude.…”

Seismic Protection of Monuments and Historical Buildings by a Sustainable Reduction System of the Seismic Input Motion

“…A great help to the subject under consideration was given by the analysis of the strong motion array records obtained from the various strong motion arrays as it is presented by [7], [19], [20], [21], [22], [23] and many other researchers. Besides this, the practical interest lays on the establishing of time histories of strong motion for the seismic analysis of structures with multiple supports, long structures e.tc..…”

“…On the other hand as it is concluded by [21] the peak cross correlation values (P) of the accelerogramms, of the El Centro Differential Array may be approximated by the expression:…”

“…(4) it is concluded by [21], that the frequency (f) and the length of the foundation (L), as far as the reduction of the input seismic motions is concerned, are interchangeable quantities. This means that we can get the same values of cross correlation either by long lengths of foundations or by high predominant frequencies of the seismic ground motion.…”

Introduction to the Special Issue on Rotational Seismology and Engineering Applications

“…For example, Graizer (1991) recorded tilts and translational motions in the near field of two nuclear explosions using seismological observatory sensors to directly measure point rotations. Nigbor (1994) directly measured rotational and translational ground motions and observed significant amounts of near-field rotational motions near a large explosion using commercial rotational sensors.Rotations and strains of the ground and of response of structures have been deduced indirectly from accelerometer arrays using methods valid for seismic waves having wavelengths that are long compared to the distances between sensors (e.g., Castellani and Boffi, 1986;Niazi, 1987;Oliveira and Bolt, 1989;Spudich et al, 1995;Bodin et al, 1997;Huang, 2003;Ghayamghamian and Nouri, 2007;Spudich and Fletcher, 2008). The rotational components of ground motion have also been estimated theoretically, using kinematic source models and linear elastodynamic theory of wave propagation in elastic solids (e.g., Bouchon and Aki, 1982;Trifunac, 1982; Trifunac, 1985, 1987).…”