Site Effect Evaluation Using Combination of Source Scaling Models and Ground Motion Records

We analyze site response of the Taipei basin using the records obtained by the Taiwan Strong Ground Motion Instrumentation Program (TSMIP) network. Records of 66 earthquakes of M=2.6-6.5 with a hypocentral depth varying from 1 km to 118 km and hypocentral distances of up to 150 km are studied for 35 stations located within this triangle shaped alluvium structure. The site response is obtained in terms of spectral ratios calculated by dividing of the site spectrum by the reference spectrum estimated for a hypothetical “very hard rock” site. The recently developed empirical source scaling and attenuation models are used for the reference spectra calculation. This approach allows us to evaluate the variability of spectral ratios due to uncertainties introduced by source and propagation path effects and variability in the site response itself. The characteristics of site response in the Taipei basin depend on the properties of soil deposits and, in general, may be described by I-D models. However, there are some peculiarities of spectral ratios that show the influence of subsurface topography

Probabilistic Microzonation of Urban Territories: A Case of the Taipei City

An integrated approach for evaluating “site-dependent” seismic hazard in terms of ground-motion parameters, which are used for engineering purposes, is presented. The method is based on the probabilistic seismic hazard analysis in terms of Fourier acceleration spectra. A scheme that allows conversion of the Uniform Hazard Fourier spectra to “hazard-compatible” peak ground acceleration (PGA), and Uniform Hazard response spectra is described. The method has been applied for preliminary probabilistic microzonation of the Taipei basin (the Taipei city). The source, path and site effects are characterized separately on the basis of the analysis of large collection of ground-motion recordings obtained since 1991 in Taiwan area. The probabilistic microzonation maps of the Taipei basin were compiled for various return periods and were compared with the data from recent strong earthquakes. It has been shown that Peak Ground Acceleration and amplitudes of the Uniform Hazard Response spectra strictly depend both on the local site conditions and on the characteristics of seismicity (the depth and location of earthquakes, and azimuthal direction of incident excitation). Therefore, one single building code is not adequate for the whole basin area. The obtained “Region & Site & Return period-dependent” estimations may be used as a reliable basis for building code provisions and engineering decisions