Journal Article

Characterizing site-specific ground motion at great depth in a low seismicity region: challenges and perspectives for a nuclear waste repository project

Contrucci, Isabelle, Ameri, Gabriele, Shible, Hussein, Baumont, David, Ego, Frederic

2023

Overview

The quantification of earthquake-generated site-specific ground motions is necessary for accurate and reliable seismic hazard assessment for critical structures. To this aim, empirical and numerical approaches are typically used in order to characterize the site response at the target site. This is not straightforward in low-seismicity regions and even more challenging when the target structure is located at great depth. This article, focusing on a practical application for an underground radioactive waste repository project to be located in the eastern part of the Paris Basin (France), presents and discusses the results and the faced challenges in the characterization of the site transfer function (TF) from surface to several depths as well as when assessing the applicability of the ergodic site terms from empirical ground motion models to the target site. We first present the data collected in the last years at the project site and the empirical TFs between the surface and two locations at depth (–490 m and –445 m). The empirical transfer function is robust in the frequency range 0.5–10 Hz and less reliable above 10 Hz due to the reduced number of usable recordings. A good consistency is found with the numerical transfer function based on a 1D soil model derived from local boreholes data. A transfer function based on noise recordings is also computed and compared to the earthquake-based one showing a good agreement of the horizontal components. These results clearly open several perspectives on the potential use of ambient noise data and numerical modelling in order to quantify the site response at any point of the underground project layout. Then, we investigate the site-specific high-frequency decay parameter κ 0 using the available earthquake recordings at the surface. The estimates of κ 0 obtained combining both acceleration- and displacement-based approaches are affected by large uncertainties owing mainly to the lack of data at short distances (< than 100 km). Nonetheless, a range of κ 0 values having a central κ 0 =0.042 s and lower and upper bounds of 0.02 s and 0.058 s is proposed and V s - κ 0 adjustment factors are calculated using the IRVT approach (Al Atik 2014 BSSA 104:336–346 ) for few example cases. Such adjustment factors together with the empirical TFs and related uncertainties can be used to remove the ergodic assumption on the site term of GMMs in order to improve classical ergodic seismic hazard assessment for structures at surface and at depth.

• Publisher: Springer Netherlands,Springer Nature B.V,Springer Verlag
• Subject: Ambient noise / Boreholes / Civil Engineering / Depth / Earth and Environmental Science / Earth Sciences / Earthquakes / Environmental Engineering/Biotechnology / Ergodic processes / Frequency ranges / Geological hazards / Geophysics/Geodesy / Geotechnical Engineering & Applied Earth Sciences / Ground motion / Hazard assessment / Hydrogeology / Mathematical models / Numerical models / Original Article / Radioactive wastes / Repositories / Robustness (mathematics) / Sciences of the Universe / Seismic activity / Seismic hazard / Seismicity / Structural Geology / Transfer functions / Uncertainty / Upper bounds