The New Formula of Seismic Rigidity Method

Rigidity Method

This publication is a revised version of the Rigidity Method previous article. Seismic rigidity method despite its widespread use is the object of harsh criticism from scientists who oppose it to the methodology and results of seismological registration of earthquakes and microseisms. The article substantiates the original approach based on the solution of the direct problem of seismic microzonation for the model of real soil thickness. A new formula of the seismic rigidity method is proposed, taking into account the lithological, hydrogeological and spectral features of the soil mass, as well as the position of the new seismic scale of the SSI. The formula was tested on the example of the correct description of the features of macroseismic effects on the territory of Leninakan at the Spitak earthquake in 1988. Linear estimates according to the formula of seismic rigidity in the seismic microzoning area represent changes in seismic intensity in the most contrast way. It is shown that the real estimates of seismic intensity under strong seismic effects (by I > VII degree) will not exceed those given by the formula of the seismic rigidity method.

The seismic rigidity method (SRM) is historically one of the first instrumental methods of assessing the impact of soil properties on the parameters of seismic effects, which currently causes a contradictory attitude. On the one hand, it is the most frequently used method of seismic microzonation (SMZ); on the other hand, it is hardly possible to find in the arsenal of SMZ methods another method that is subjected to such fierce and diverse criticism. It should be noted that this criticism is not presented in the form of printed articles, but constantly arises in various discussions, in private opinions, etc., which only complicates public discussion. What to be considered and what to reject? This article attempts to understand this interesting and important from the practice point of view question. This publication is a revised version of the previous article [1] .

For the quantitative ratios, linking the soil properties with changes in seismic intensity S. V. Medvedev [2] was used the dependence of seismic intensity from three factors: the value of seismic rigidity―the product of elastic wave velocity on density, groundwater level and resonance phenomena in the thickness of the soil. Formally, this dependence is expressed by the relation: ΔIΣ=ΔIS+ΔIW+ΔIRΔIΣ=ΔIS+ΔIW+ΔIR , where consistently spelled out the above-mentioned factors. Consider each of the factors in more detail.