Empirical Quantification of the Impact of Nonlinear Soil Behavior on Site Response
REGNIER ; CADET ; BARD
Type de document
ARTICLE A COMITE DE LECTURE REPERTORIE DANS BDI (ACL)
Langue
anglais
Auteur
REGNIER ; CADET ; BARD
Résumé / Abstract
We present an extensive analysis of the quantitative impact of the nonlinear soil behavior on site response at 174 sites of the Japanese Kiban-Kyoshin (KiKnet) network. The nonlinear to linear siteresponse ratio (RSRNLL) is calculated by comparing the surface/downhole Fourier spectral ratio for strong events and for weak events. Three thresholds of surface peak ground acceleration (PGA) are tested to characterize the strong events: 100, 200, and 300 cm/s2, whereas weak events correspond to surface PGA in the 0.1-25 cm/s2 range. This ratio exhibits a typical shape; with a lowfrequency part above 1 and a highfrequency part generally below 1, separated by a transition zone around a sitedependent frequency labeled fNL (characterized by RSRNLL=1). The average maximum amplitudes of RSRNLL are 1.4, 1.5, and 1.6, and the minimums are 0.6, 0.5, and 0.5 for PGA thresholds 100, 200, and 300 cm/s2, respectively, showing that nonlinear soil behavior results in significant siteresponse modifications even for moderate PGA values of 100 cm/s2. The fNL value exhibits a satisfactory correlation with site classifications based on either VS30 (traveltime averaged shearwave velocity over the top 30 m) or f0 (site fundamental frequency): fNL decreases when either VS30 or f0 decreases. In addition, the amount of the lowfrequency amplification increase depends on VS30 and reaches a maximum of 1.6 for high VS30 soil classes associated with shallow thin softsoil layer underlain by stiff substratum. The average highfrequency decrease is about 0.5 for all soil classes defined from either VS30 or f0; for a few sites, however, this decrease is replaced by an increase as reported in previous studies, in relation with water contents and porepressure issues. The increase of amplification below fNL is found to be a quasisystematic consequence of nonlinear soil behavior, which should be emphasized, because it can reach up to 1.6 for high VS30 sites.
Source
Bulletin of the Seismological Society of America, num. 4, pp.1710-1719 p.
Editeur
Seismological Society of America
