Identification of Nonlinear Behavior of Soils in Strong Earthquakes

O.Pavlenko (Institute of Physics of the Earth, Russian Academy of Sciences, Moscow, Russia); K.Irikura (Disaster Prevention Research Institute, Kyoto University, Kyoto, Japan)

e-mail: olga@synapse.ru

The purpose of the study is quantitative description, in terms of higher-order transfer functions, of the nonlinear soil behavior in strong earthquakes. Records of strong earthquakes, provided by seismic vertical arrays, represent valuable experimental data, allowing estimation of the soil behavior at different depths. We propose the method for estimation stress-strain relations in soil layers from the surface down to the location of the deepest device and the following nonlinear identification of the soil behavior. As an example, records obtained during the 1995 Kobe earthquake (Japan) at vertical array sites located within 10 km from the epicenter are used. The results show that: (1) the behavior of the upper 0.15 m of the soil profiles was dynamically unstable; (2) soils represent physical systems possessing mostly odd types of nonlinearity, whereas even-order nonlinearities become comparable with odd-order ones in liquefied soils; (3) as liquefaction develops, the nonlinear part of the soil response (in horizontal components) increases from ~30% up to ~60% due to the increase of even-order nonlinear components; (4) on the whole, nonlinearity of soils leads to changes in spectra of propagating seismic signals so that spectra tend to take the form of E(f)~f^n.


Section : 6