The extremely shallow MW 4.9 2019 Le Teil earthquake, France: main ground motion features and comparison with ground motion models

On 11 November 2019, a MW 4.9 earthquake occurred in Le Teil, southeastern France, at an exceptional depth of 1 to 2~km. We benefit from a comprehensive dataset of high-quality seismic records to investigate ground motion features in terms of source, path, and site effects. Clear regional variations of intensity measures are identified. Additionally, we conduct a residual analysis by comparing observed motions with predictions from ground motion models (GMMs), revealing a systematic underestimation of amplitudes at low frequencies (< 1 Hz), associated with the generation of Rayleigh waves. These waves are generated due to the shallow depth of the rupture and are most prominent in directions orthogonal to the fault. At higher frequencies, additional spatial variations are observed. In particular, ground motions recorded in the southeast show significantly lower amplitudes than those predicted by GMMs. This phenomenon may be attributed to the regional attenuation and geological structure or to local geological conditions combined with the extremely shallow depth of the seismic event, as demonstrated with numerical simulations. Our study emphasises the necessity for further analyses of ground motions generated by such moderate extremely shallow earthquakes.