Modeling of Empirical Transfer Functions Including 3D Velocity Structure

Date: 4/26/2019

Time: 06:00 PM

Room: Grand Ballroom

Site response can be an important factor in estimating seismic hazard. However, conventional simplified modeling of site amplification with assumptions of plane SH waves propagating vertically through layered homogeneous media often poorly predicts the empirical transfer function (ETF), particularly where large lateral variations of velocity are present. Here, we use physics-based simulations that naturally incorporate the complex subsurface material properties and provide synthetic ground motions to compute theoretical transfer functions (TTF). We calibrate the 3D subsurface geometry by means of the topography near the sites and incorporate information from a suite of Vs profiles obtained from borehole logs. By comparing TTFs to the estimated ETFs at selected sites (e.g. the KiK-net sites and the Garner Valley Downhole Array site), we show how simulations in the calibrated 3D medium, including statistical distributions of small-scale heterogeneities, are able to adequately model the site amplification. We show that the velocity variations play a considerable role in determining both the frequency and amplitude of the site response. Properly calibrated spatial variation of the sediments below the site, including the slope of the edges and the depth to the bedrock, significantly improves the fit to the ETFs. In some cases, the Vs profiles derived from the borehole measurements are unable to produce TTFs consistent with the observed ETFs. The results emphasize the importance of reliable calibration of subsurface structure and material properties in site response studies.

Presenting Author: Zhifeng Hu

Authors