Nonlinear Behavior of Soils Revealed from the Records of the 2000 Tottori, Japan, Earthquake at Stations of the Digital Strong-Motion Network Kik-Net

Abstract

Acceleration records of the Tottori earthquake (6 October 2000), pro- vided by stations of the Digital Strong-Motion Network Kik-Net, show clear evidence of the nonlinearity of soil response at sites located in near-fault zones. In this study, records of the mainshock of the Tottori earthquake are analyzed, and stresses and strains, induced by the strong motion in the upper 100 or 200 m of soil, are recon- structed at sites located within 80 km from the fault plane. For reconstructing stresses and strains, the method is applied, which we developed and used previously for studying the response of soils during the 1995 Kobe earthquake. Nonlinear time- dependent stress-strain relations in the soil layers are estimated based on vertical- array records. A good agreement between the observed and simulated accelerograms of the Tottori earthquake testifies to the validity of the obtained vertical distributions of stresses and strains in the soil layers. We also evaluated variations of the shear moduli of the soil layers, caused by the strong motion, at stations located at different distances from the fault plane. Changes in the rheological properties of the upper soil layers were found at the stations closest to the fault-plane. A similarity in stress- strain relations, describing the behavior of similar soils during the 1995 Kobe earth- quake and the 2000 Tottori earthquake, was obtained, indicating the possibility of precasting soil behavior in future earthquakes at sites where profiling data are available.