Ground Motion Intensity Versus Ground Motion Kinematics. Exploring Various Intensity Measures

The interest for this topic was raised by the occurrence of the destructive Vrancea earthquake of 1977.03.04, when the first strong motion record of Romania was obtained at the Building Research Institute (INCERC) Bucharest. The attempt to assess the ground motion intensity on the basis of instrumental criteria specified by the Medvedev-Sponheuer-Karnik (MSK) intensity scale failed, due to strongly divergent results obtained by means of using the peak ground acceleration (PGA) and peak ground velocity (PGV) criteria. This failure was due to the fact that the inflexible MSK criteria referred to relied on the implicit non-realistic assumption that all ground motions are characterized by an invariable velocity/acceleration corner period of 0.5 s. A flexible Spectral Intensity Assessment System (SIAS) relying on ground motion accelerographic information was developed. This makes it possible to estimate, according to needs, global intensity, frequency related intensity, intensity averaged upon a spectral band etc. Alternative basic kinematic ground motion characteristics for global intensities and for frequency related intensities were introduced. Correlation analysis performed revealed quite strong correlations between results of using alternative criteria. Characteristic parameters were calibrated and alternative calibrations are discussed. Some illustrative cases are presented. Comments and recommendations are finally presented.