Frequency-dependent Response of Soft (Sandy and Loess) Soils in Seismic Motion and Seismic Rigidity Method

Abstract

With this work, we start studying of the response of soils of various types (among 11 types of the most representative surface soils on the territory of Russian Federation) in seismic motion, based on in situ observations (KiK-net data). The response of soft sandy and loess soils to weak and medium-intensity seismic motion is analyzed. We show that the response of rather homogeneous soil pro­les (without clear seismic boundaries) to seismic motion is frequency-dependent and contains resonant frequencies, at which seismic motion is noticeably enhanced. At stronger seismic motion, the resonant frequencies are reduced, and the ampli­cation of seismic motion by soil layers is also reduced. These e€ects are not taken into account in seismic rigidity method, the application of which is still required by the Building codes acting in Russia.
 We should change the practice of application of the seismic rigidity method in the Building codes, by clearly de­ning the scope of the method, and we should move to the spectral description of the corrections for ground conditions in earthquake resistant construction, by means of response spectra, as done in other countries.