The Site Effect Analysis of Semi-Cylindrical Canyons and Soft Alluvial Basins by H/V Spectral Ratio

The source, path and site effects are the main causes for ground motions. Soft alluvial basins especially result in seismic wave amplification as the site effect. Irregular alluvial basins and canyons in this study are semi-cylindrical for simplifying analysis. To deal with the scattering problems in frequency domain, Yeh et al. have gained positive outcomes by using a hybrid method which combined finite elements and the series expansion method to effectively solve the scattering problem in the irregular basins. These displacements derived from the frequency domain are computed with the H/V ratio to estimate the site effect. As the site effect is crucial in earthquake engineering, this study may serve as a quantitative contribution towards the amplified effect in alluvial basins and canyons. It can also simulate the effects of different incident angles on the H/V ratio.

Site Effects for the Sacramento-San Joaquin Delta

Seismic site response and site effects models are presented for levees in the Sacramento-San Joaquin Delta where the subsurface soils include thick deposits of highly organic soils. Sources of uncertainty that contribute to the variation of seismic wave amplification are investigated, including variations in the input ground motions, soil profiles, and dynamic soil properties through Monte Carlo simulations of equivalent-linear site response analyses. Regression models for seismic wave amplification for levees in the Delta are presented that range from a function of peak outcrop acceleration alone to a vector of response spectra ordinates and soil profile parameters. The site effects models were incorporated into a probabilistic seismic hazard analysis for a representative location, and the relative impacts of the various models on the computed hazard are evaluated.