Adjusting an active shallow crustal ground motion model to regions with scarce data: application to France

The objective of this work is to test whether an empirical Ground Motion Model (GMM) developed for high-seismicity regions can be effectively adapted to a neighbouring region with lower seismic activity. We select the ITA18 suite of GMMs (Lanzano et al. in Bull Seismol Soc Am 109(2): 525-540, 2019a), developed for Italy, which is a region dominated by moderate-to-strong shallow crustal earthquakes, and assess their applicability to Continental France, where the seismic activity is less frequent and characterised by lower magnitudes. Based on a dataset of more than 2300 records of events with 3.0 ≤ M W ≤ 5.2, occurred in France in the time interval 1996–2019 (named FR20), we perform a residual analysis and calibrate an adjustment factor for both horizontal and vertical-to-horizontal (VH) components of Peak Ground Acceleration, Peak Ground Velocity, and 5% damped Spectral Acceleration (SA). Apart from the median correction, no modification of the scaling with magnitude, focal mechanism, and V S,30 is introduced, while the distance scaling is adjusted to capture the lower anelastic attenuation of the French data. In addition, to overcome the underestimation of the ITA18 model for the short period VH spectral amplitudes in the near-source region (R epi