On Estimation of Dominant Vibration Periods of Site

Abstract

Analysis of data of macroseismic inspection of consequences of strong and destructive earthquake shows, that quite often the cause of destruction or of amplification of seismic effect is connected with resonant phenomena in the soil-construction system.

There is a lot of example of such behaviour: Mexico (1985), Spitak(1988), etc.

This makes definition of dominant frequencies of vibrations of soil layer on which the construction is or will be built very important for increasing object’s safety.

In the paper some methodical aspects of estimation of dominant periods are analyzed. The techniques, suggested by K. Kanai and Y. Nakamura are compared. The last one, based on the comparasion of spectra of horizontal and vertical oscillations (H/V ratio) unexpectedly has found very wide application all over the world.

In both methods the study of microtremors in an essential point. It has been proved, nevertheless that their application is not always justified. The examples of determination of dominant vibration periods of soil layer by Nakamura approach and by modern powerful artificial vibration sources (pulse sources and vibrators).

It is shown that at intensive loading the oscillation periods variation on attain 2030% or more of initial, value.

Instrumental recordings et of magnitudes M=1.8-8.2 earthquakes obtained in varies regions of the world with various soil conditions.

It is shown that it is possible to standardize physical state of soil layer or their seismic properties using values of dominant periods of vibration of soil, which is important for practical purposes.