Geometrical focusing as a mechanism for significant amplification of ground motion in sedimentary basins: Analytical and numerical study

Shahar Shani-Kadmiel, Michael Tsesarsky, John N. Louie, Zohar Gvirtzman

Research output: Contribution to journalArticleScientificpeer-review

9 Citations (Scopus)

Abstract

We study the geometrical and material conditions which lead to focusing of seismic waves traveling across a concave velocity interface representing the boundary of a sedimentary basin within a denser rock. We approximate, using geometrical analysis for plane-waves, the combination of interface eccentricities and velocity ratios for which the seismic rays converge to a near surface region of the basin. 2-D finite difference modeling is used to compute Peak Ground Velocity (PGV) and spectral amplification across the basin. We show that effective geometrical focusing occurs for a narrow set of eccentricities and velocity ratios, where seismic energy is converged to a region of ± 0.5 km from surface. This mechanism leads to significant amplification of PGV at the center of the basin, up to a factor of 3; frequencies of the modeled spectrum are amplified up to the corner frequency of the source. Finally, we suggest a practical method for evaluating the potential for effective geometrical focusing in sedimentary basins.

Original languageEnglish
Pages (from-to)607-625
Number of pages19
JournalBulletin of Earthquake Engineering
Volume12
Issue number2
DOIs
Publication statusPublished - 1 Jan 2014
Externally publishedYes

Keywords

  • Alluvial valley response
  • Geometrical focusing
  • Ground motion amplification
  • Sedimentary basin response
  • Seismic wave propagation
  • Site response

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