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Extension of the Basin Rayleigh-Wave Amplification Theory to Include Basin-Edge Effects

Brissaud, Quentin and Bowden, Daniel C. and Tsai, Victor C. (2020) Extension of the Basin Rayleigh-Wave Amplification Theory to Include Basin-Edge Effects. Bulletin of the Seismological Society of America, 110 (3). pp. 1305-1322. ISSN 0037-1106. https://resolver.caltech.edu/CaltechAUTHORS:20200506-125019256

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Abstract

The presence of sediments near the Earth’s surface can significantly amplify the strength of shaking during earthquakes. Such basin or site amplification effects have been well documented in numerous regions, yet the complex and often situational dependence of competing reasons for this amplification makes it hard to quantify in a general sense or to determine the most significant contributions. Simple 1D seismic profiles can be used to estimate the amplitude differences between a basin site and a hard‐rock reference site, but this ignores any reflections or conversions at the basin edge or a resonance effect depending on the basin’s geometry. In this article, we explore an analytic model based on coupling coefficients for surface Rayleigh waves to account for the lateral discontinuities at a basin’s edge (Datta 2018). We use this simple tool to explore the relationship between the basin’s Rayleigh‐wave amplification spectrum and various parameters such as basin depth, edge slope angle, and impedance contrast. The step‐by‐step construction of the model allows us to quantify the contributions from various wave propagation effects with the goal of identifying situations under which various basin‐edge effects must be considered in addition to purely 1D estimates. For the most velocity contrasts (less than a factor of 5), the error made by the 1D theory in predicting maximum Rayleigh‐wave basin amplification is under 35% for both the horizontal and the vertical components. For simple basins, the vertical amplification dominates at larger high frequencies and the horizontal at lower frequencies. Finally, we demonstrate from comparisons with spectral‐element wavefield simulations that realistic velocity structures can be reduced to a simpler “box” shape for the semi‐analytic formulation used here with reasonable results. For the purposes of estimating site‐amplification or microzonation, an improved model that accounts for basin‐edge effects can be implemented without high‐computational cost.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1785/0120190161DOIArticle
ORCID:
AuthorORCID
Brissaud, Quentin0000-0001-8189-4699
Bowden, Daniel C.0000-0003-3332-5146
Tsai, Victor C.0000-0003-1809-6672
Additional Information:© 2020 Seismological Society of America. Manuscript received 21 June 2019; Published online 7 April 2020. The authors thank Arjun Datta for discussion about his work and for providing his code to compute surface‐wave transmission and reflection coefficients. Data and Resources: The velocity and density profiles used in this study were extracted from the Southern California Earthquake Data Center (SCEDC), model CVMS4.26 https://scec.usc.edu/scecpedia/UCVM/ (last accessed March 2020). Scripts to compute surface‐wave transmission and reflection coefficients (SWRT) are available at https://github.com/arjundatta23/SWRT/ (last accessed March 2020). The SPECtral Finite EleMents (SPECFEM) package is available at https://geodynamics.org/cig/software/specfem2d/ (last accessed March 2020). The supplementary material contains additional information about the Green’s functions analytical expressions and extra figures describing near‐field effects, the variations of dominant frequency with velocity ratios, the horizontal maximum amplification sensitivity against basin‐shape ratio and location within the basin, and comparing amplification spectra from the different theories at another location in the Los Angeles basin. The supplementary material also describes the wavefield composition in semi‐infinite basins and the spatial and frequency dependence of vertical and horizontal amplification spectra for semi‐infinite and closed basins.
Group:Seismological Laboratory
Issue or Number:3
Record Number:CaltechAUTHORS:20200506-125019256
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20200506-125019256
Official Citation:Quentin Brissaud, Daniel C. Bowden, Victor C. Tsai; Extension of the Basin Rayleigh‐Wave Amplification Theory to Include Basin‐Edge Effects. Bulletin of the Seismological Society of America ; 110 (3): 1305–1322. doi: https://doi.org/10.1785/0120190161
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:103037
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:06 May 2020 19:56
Last Modified:02 Jun 2020 17:01

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