Using ambient noise to investigate slope instabilities induced by the 2008 Wenchuan earthquake (Sichuan, China)

Ambient noise recordings were acquired at sites affected by slope failures during the Mw 7.9 Wenchuan earthquake of May 12th, 2008 (Sichuan Province, China) in order to investigate the role of site amplification in slope destabilisation. Data were processed using a technique based on instantaneous polarisation analysis to derive Rayleigh wave characteristics correlated to site dynamic response properties like resonance frequencies and maximum amplification directions. These properties can be revealed by the observation of pronounced peak values of H/V ratios between horizontal and vertical components of ground motion at site specific frequencies and directions. The analysis results showed that, in comparison to "reference" sites, where no evidence of a preferential polarisation was observed, ground motions at most of the sites on slopes were preferentially oriented along directions related to local structural and/or morphological features (~perpendicular to fault systems, ~parallel or perpendicular to relief elongation).