Encyclopedia of Engineering Geology

2018 Edition
| Editors: Peter T. Bobrowsky, Brian Marker

Ground Motion Amplification

  • David A. GunnEmail author
Reference work entry
DOI: https://doi.org/10.1007/978-3-319-73568-9_146


Local ground response; Site amplification; Site effects; Site response


The increase in amplitude of seismic waves as they pass from faster to slower geological units, plus increases in amplitude due to interactions within more complex structures containing soft sediments.

Ground motion amplification (GMA) is defined as the ratio of the ground motion at the surface of the surficial (or soil) outcrop with respect to the ground motion at bedrock outcrop at the same site. Quantitative GMA factors can be defined using any ground motion parameter, but GMA is most commonly expressed as the ratio of the spectral accelerations at the specific time period of these motions (Kramer 1996; Bowden and Tsai 2017).

Amplification Processes

A horizontally layered sequence with an abrupt increase of shear wave velocity and/or density will cause ground motion amplification. Thus, alluvial basins, deltas, and lake deposits are places where one would expect GMA during earthquake induced...

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Authors and Affiliations

  1. 1.British Geological SurveyKeyworthUK