Nonlinear identification of the soil response at Dahan downhole array site during the 1999 Chi-Chi earthquake

Records of the 1999 Chi-Chi earthquake, provided by the Dahan downhole array were analyzed, and nonlinear hysteretic stress-strain relations in the soil layers were estimated by the method previously used for studying the response of soils during the 1995 Kobe and the 2000 Tottori earthquakes. The obtained models of the soil behavior were applied for evaluating changes of the shear moduli in the soil layers and for the nonlinear identification of the soil behavior at Dahan site during the Chi-Chi earthquake. We found that reduction of the shear moduli in the soil layers did not exceed ∼5%, and the soil response was virtually linear. The content of the nonlinear components in the soil response was about 5% of the intensity of the response, and it was mostly due to the odd-order nonlinearities. A similarity in the stress-strain relations describing the behavior of soils during the 1995 Kobe earthquake, the 2000 Tottori earthquake, and the 1999 Chi-Chi earthquake was found, which indicates the possibility to describe the behavior of similar types of soils at different sites by similar stress-strain relations and predict soil behavior in future earthquakes.