Hualien seismic downhole data analysis

The Hualien, Taiwan, large-scale seismic test (LSST) was initiated in 1993 by a consortium of industrial and research enterprises from five countries (Japan, USA, Taiwan, France and Korea). This in situ LSST includes two five-accelerometer free-field downhole arrays that recorded site response during seven earthquakes (1993–1995). In this paper, the seismic site response during two of these events is analyzed. Correlation analyses of the recorded downhole accelerations are performed to calculate an average shear wave velocity profile. In addition, the actual seismic shear stress–strain histories are directly calculated from the recorded downhole lateral accelerations. These histories are then used to estimate soil stiffness and material damping in the linear, small-strain range. The estimated soil stiffness is found to be significantly different in the longitudinal and transverse directions, which suggests a marked azimuthal variation of soil properties (anisotropy). In a recent study of seismic site response, Ueshima and Okano (Further investigation of seismic response of soil and embedded structure in Hualien LSST program. Proceedings of Eleventh World Conference on Earthquake Engineering, Acapulco, Mexico, 1996) also arrive at this interesting conclusion. In addition, this anisotropic soil response appears to have been manifested during earlier in situ experimental studies of foundation impedance functions (Barros and Luco, 1995, Identification of foundation impedance functions and soil properties from vibration tests of the Hualien containment model. Soil Dynamics and Earthquake Engineering 14, 229–248). Finally, the identified linear soil properties are shown to represent adequately the recorded seismic site response at small strains.