Satellite imagery strategies for mapping site resonance periods at fine spacial scale

2024

Colloque

Schindelholz V., Cheaib A., Maufroy E., Cornou Cécile, Pathier E., Schlupp A.

18th World Conference on Earthquake Engineering

[s.l.] : [s.n.], 2024, 13 p. multigr.

World Conference on Earthquake Engineering (WCEE), 18., Milan (ITA), 2024-06-30-2024-07-05

Seismic waves emitted during an earthquake are characterized by their type and propagation velocity. The velocity of shear waves (VS) at the near-surface varies from 1000 m/s to less than 50 m/s, depending on the soil characteristics. The presence of poorly-rigid geological deposits can lead to important seismic ground-motion amplifications called site effects. Site effects can make earthquakes much more aggressive to buildings, resulting in significantly increased damage. The site effects can be characterized by several proxies such as VS30, soil resonance period, surface geology and geotechnical parameters. The resonance period is one of the most relevant proxies as it accounts for the vibrational properties of the whole soil column. However, measuring resonance periods at fine spatial scale over wide areas with classical methods such as the H/V method requires a lot of measurement points which is a tedious task. As both the resonance period and the compaction rate of the sedimentary cover increase with sediment thickness and site softness, our study aims at investigating the relationship between the resonance period and the subsidence rate obtained by satellite imagery in France. We propose an innovative methodology that takes advantage of satellite SAR Interferometry time series analysis, providing subsidence rates at millimetric precision. We base our study on the Grenoble valley (southeastern France) where numerous geophysical and geological data collected over the last 25 years are available: bedrock depth map, VS30 map, S-wave velocity profiles, hundreds of resonance period measurements, hundreds of geotechnical and geological drillings, levelling measurements, SAR time series. Subsidence rates are compared to the various available geophysical and geological data related to near-surface and deep soil characteristics. The subsidence rate measured in the Grenoble valley is mostly caused by the compaction of the stiff and thick sediments due to natural (input of sedimentary materials on the surface) and anthropogenic (urbanization) overloading. Our analysis outlines that subsidence rates are linearly correlated with both the resonance periods and the depth of the seismic bedrock, which indicates the ability of satellite imagery to provide resonance periods at a very fine spatial scale

Géologie et formations superficielles [064] ; Géophysique interne [066]

Fonds IRD [F B010091624]

fdi:010091624