Séminaire ISTerre

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Recent developments in site response studies : 1) uncertainty projected mapping of site response and 2) instrumental evidence of topography-induced site response using ambient vibrations

mardi 19 septembre 2023 - 13h30

Anirban Chakraborty - Hosei University, Japan
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TALK 1: UNCERTAINTY PROJECTED MAPPING OF SITE RESPONSE : Seismic risk assessments at the regional level require site-response maps of appropriate spatial resolution. As site-specific data at each location is seldom available, using proxies (e.g., slope, geology, etc.) to spatially interpolate (mean) site responses is common practice. However, such methods yield identical uncertainty at every location, irrespective of prior site-specific data. In this talk, I introduce Uncertainty Projected Mapping (UPM), a Bayesian approach generating site-response maps with varying spatial resolutions and uncertainties based on the significance of local site-response variability. This Bayesian framework uses empirical site responses at data-available stations as likelihoods against non-informative or informative priors. The resulting posteriors compose the site-response maps, which can be further refined with the availability of new site-specific data. In this talk, case studies of the application of UPM to site-response mapping in Japan and Italy will be discussed. TALK 2: INSTRUMENTAL EVIDENCE OF TOPOGRAPHY-INDUCED SITE RESPONSE USING AMBIENT VIBRATIONS : Amplification of earthquake ground motions due to topography has been observed during past earthquakes. This phenomenon could lead to highly damaging landslides in the mountainous areas. However, as the data availability in mountainous regions is limited, the topographical amplification is still poorly understood. Recently, ambient vibration studies have been employed to understand this phenomenon. This talk discusses the results of ambient vibration case studies from two mountains in Japan. These mountains, with 73 m and 327 m prominence, are selected to be free-standing as much as possible. Accelerometers are temporarily employed at the base and summit of the mountains, and spectral amplifications are calculated from the corresponding ratio of Fourier spectra. The spectral amplification plots in both cases show the clear presence of a peak. The role of resonance in explaining the peak of these spectral amplification plots is being investigated. The results are significant from the point of view of assessing the potential of earthquake-induced landslides when earthquake scenario ground motions are available.

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Equipe organisatrice : Géophysique des Risques et de l’Environnement

Salle Dolomieu, Maison des Géosciences, 38400 Saint Martin d'Hères

Informations de visio :

https://univ-grenoble-alpes-fr.zoom.us/j/96663779535?pwd=MmViT0RmdnRWanEzYm12TDNHWm9Tdz09