2D ground motion at a soft viscoelastic layer/hard substratumsite in response to SH cylindrical seismic waves radiated by deepand shallow line sources

Abstract : We show, essentially by theoretical means, that for a site withthe chosen simple geometry and mechanical properties (horizontal,homogeneous, soft viscoelastic layer of infinite lateral extent overlying, and in welded contact with, a homogeneous, hard elastic substratum of half-infinite radial extent, shear-horizontal motion):1) coupling to Love modes is all the weaker the farther theseismic source (modeled as a line, assumed to lie in the substratum) is fromthe lower boundary of the soft layer, 2) for a line source closeto the lower boundary of the soft layer, the ground response ischaracterized by possible beating phenomena, and is ofsignificantly-longer duration than for excitation by cylindricalwaves radiated by deep sources. Numerical applications of thetheory show, for instance, that a line source, located 40m belowthe lower boundary of a 60m thick soft layer in a hypotheticalMexico City-like site, radiating a SH pulse of 4s duration,produces substantial ground motion during 200s, with markedbeating, at an epicentral distance of 3km. This response is insome respects similar to that observed in real cities located atsoft-soil sites so that the model employed herein may help toestablish the causes and pinpoint the major contributing factorsof the devastating effects of earthquakes in such cities.
Type de document :
Pré-publication, Document de travail
OR 15. Submitted to Geophys.J.Intl. 2004
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Armand Wirgin, Jean-Philippe Groby. 2D ground motion at a soft viscoelastic layer/hard substratumsite in response to SH cylindrical seismic waves radiated by deepand shallow line sources. OR 15. Submitted to Geophys.J.Intl. 2004. 〈hal-00001043〉

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