Variations in Site Response Across Urban High Impedance Contrast Basins

Session: Near-Surface Effects: Advances in Site Response Estimation and Its Applications [Poster]
Type: Poster
Date: 4/28/2020
Time: 08:00 AM
Room: Ballroom
Description: 

Seismic hazard research shows that there is an amplification of seismic waves where soft sediments overlay bedrock, which has implications on human and structural safety in major cities across the globe. This amplification can be attributed to the impedance contrast between the sediments and bedrock, where high impedance contrasts lead to significant amplifications. Additionally, one-dimensional vertical wave propagation through the soil layer and/or three-dimensional wave propagation effects across a sedimentary basin influence the magnitude of amplification at a given site. When the propagation behavior is one-dimensional and well-behaved, namely vertically propagating waves through horizontally-layered media (e.g. SH1D assumptions), the site response may be well predicted by the velocity profile of the underlying column of media (sediment and bedrock). However, when three-dimensional wave propagation effects are in-play, regional information around basin shape and velocity heterogeneities should be incorporated into site response analyses. Through comparison of the near surface amplification in two high-impedance contrast sedimentary basins: Boston, Massachusetts, USA and Mexico City, Mexico, we identify 1D and 3D contributions to amplification and provide insight into potential prediction methods of site amplification in similar high-impedance contrast environments.

We utilize the Horizontal to Vertical Spectral Ratio (HVSR), dividing the horizontal component Fourier spectra by the vertical component Fourier spectra, on inter-event ambient noise data and/or earthquake records at each station to obtain the fundamental site period. These data are combined with prior studies in both areas, such as Yilar et al. (2017) and Pontrelli and Baise (2019) in Boston and Mexico City, respectively, to relate spatial patterns of fundamental site period and amplification ratios with characteristics of each sedimentary basin, with the goal of discriminating between 1D and 3D basin effects.

Presenting Author: Jeremy Salerno

Authors