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Extension of the basin Rayleigh-wave amplification theory to include basin-edge effects

Quentin Brissaud, Daniel C. Bowden and Victor C. Tsai
Extension of the basin Rayleigh-wave amplification theory to include basin-edge effects
Bulletin of the Seismological Society of America (April 2020) 110 (3): 1305-1322

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.


ISSN: 0037-1106
EISSN: 1943-3573
Coden: BSSAAP
Serial Title: Bulletin of the Seismological Society of America
Serial Volume: 110
Serial Issue: 3
Title: Extension of the basin Rayleigh-wave amplification theory to include basin-edge effects
Affiliation: California Institute of Technology, Pasadena, CA, United States
Pages: 1305-1322
Published: 20200407
Text Language: English
Publisher: Seismological Society of America, Berkeley, CA, United States
References: 60
Accession Number: 2020-039350
Categories: Seismology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 1 table
Secondary Affiliation: Institut fuer Geophysik, CHE, SwitzerlandBrown University, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2020, American Geosciences Institute. Abstract, Copyright, Seismological Society of America. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 202025
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