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ABSTRACT In the framework of site-specific seismic hazard assessment, the definition of reference motion is a crucial step. Reference motion is generally associated with hard-rock conditions, characterized by S-wave velocity (VS) exceeding 1500 m/s. However, ground motion recorded at sites with such conditions is underrepresented in existing strong-motion databases. Consequently, the validity domains of most empirical ground-motion models (GMMs) are not representative of reference hard-rock conditions. To address this limitation, we consider the empirical approach to retrieve and model reference ground motion for shallow crustal earthquakes in a seismically active region, proposed by Shible et al. (2023) using the Japanese Kiban–Kyoshin network data. Following this approach, we apply a deconvolution of site responses from strong-motion recordings to estimate ground motion at reference conditions in the Euro-Mediterranean region. The first step involves compiling a large database by merging the Engineering Strong-Motion Database (ESM database, Luzi et al., 2020) with additional data from the Greek, French, and Spanish networks. The second step involves estimating site response at network stations using both parametric and nonparametric generalized inversion techniques (GITs). A careful selection of reference hard-rock stations is made to constrain the inversions. The database signals are then deconvolved using the site terms obtained by GIT, allowing us to virtually bring the sites of the entire database to very high VS values, similar to outcropping bedrock conditions. GMMs are then determined for reference conditions, and the results are discussed. The derived GMMs show limited site-to-site variability (0.1–0.2 in natural log), indicating effective removal of site responses from data. In addition, an average amplification model, based on VS30, is proposed to complement the reference GMM prediction in cases where a site-specific soil response estimate is unavailable.
Shible et al. (Fri,) studied this question.