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 in cludes two five-accelerometer free-field downhole arrays that recorded site response during seven earthquakes (1993-1995). In this paper, th e seismic site response during two of these events is analyzed. Correl ation analyses of the recorded downhole accelerations are performed to calculate an average shear wave velocity profile. In addition, the ac tual seismic shear stress-strain histories are directly calculated fro m the recorded downhole lateral accelerations. These histories are the n used to estimate soil stiffness and material damping in the linear, small-strain range. The estimated soil stiffness is found to be signif icantly 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 (Furth er investigation of seismic response of soil and embedded structure in Hualien LSST program. Proceedings of Eleventh World Conference on Ear thquake Engineering, Acapulco, Mexico, 1996) also arrive at this inter esting conclusion. In addition, this anisotropic soil response appears to have been manifested during earlier in situ experimental studies o f foundation impedance functions (Barros and Luco, 1995, Identificatio n 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 properti es are shown to represent adequately the recorded seismic site respons e at small strains. (C) 1998 Elsevier Science B.V. All rights reserved .