Characteristics Of Strong Ground Motions Research Articles

土木研究所の高密度強震観測

Dense instrument array observation systems by Public Works Research Institute are described. This kind of observation systems is recently introduced at several sites in earthquake-prone areas in the world, and is expected to give useful information to clarify characteristics of strong ground motion in detail.Preliminary results of the analysis on the recorded data are also introduced in this paper, these are principal axis of the ground motion, phase velocity, amplification and the ground strain.

Earthquake Ground Motions: Implications for Designing Structures and Reconciling Structural Damage

Until recently, characteristics of strong ground motion resulting from different soil conditions were considered the dominant factor in developing design ground motions and reconciling observed damage. Interpretation of recent recordings of earthquakes by strong motion instrument arrays installed in California and Taiwan show that basic characteristics of strong motion are greatly influenced by the seismological and geological conditions. For a given soil condition, the characteristics of strong ground motion (peak ground acceleration, peak ground velocity, peak ground displacement, duration, spectral content, and time histories) can vary significantly whether the site is near or far from the seismic source. As local soil conditions only modify the ground motions produced by a given source, variability in ground motion due to seismologic and geologic conditions (for a given soil condition) must be considered in estimating earthquake ground motions for structural design or for estimating structural vulnerabilities to reconcile earthquake-related damage.

Response Spectra of Earthquake Ground Motion

In this paper a method is presented for direct scaling of Pseudo Relative Velocity Spectra (PSV) in terms of: (1)Earthquake magnitude M and epicentral distance R; or (2)Modified Mercalli Intensity (MMI) at a site. These models also depend directly on the geologic site conditions and are presented for horizontal and for vertical ground motions. This scaling is realized by means of “coefficient” functions which are determined through regression analysis of computed PSV spectra from recorded accelerograms. One of the principal advantages of the proposed method is that the ambiguities associated with the scaling of the fixed shape spectra by means of peak amplitudes of ground motion are now completely eliminated. The 91 direct regressions of horizontal and vertical spectra, at 91 periods, smoothed over all periods, lead to more complete and reliable sampling of the frequency-dependent characteristics of strong ground motion than the correlations of peak amplitudes alone.