Tracking Near-Surface Attenuation Changes Using Repetitive Anthropogenic Seismic Sources

Monitoring groundwater and near-surface processes at high temporal resolution remains challenging, particularly in urban environments. Recent advances in passive seismology have demonstrated the potential of anthropogenic seismic sources to act as stable and repeatable signals for monitoring temporal variations in seismic velocity. In this study, we extend these approaches by proposing a method to monitor near-surface seismic attenuation variations, an observable that is highly sensitive to water content and therefore particularly relevant for investigating groundwater dynamics.

We exploit train-generated seismic waves as repetitive anthropogenic sources to track temporal changes in near-surface attenuation. Using a single-station approach, we analyze variations in the frequency content and amplitudes of seismic signals generated by passing trains to infer relative changes in seismic attenuation. These variations are interpreted as proxies for changes in near-surface hydrological conditions, including water saturation and groundwater level fluctuations.

The methodology is applied to a managed water catchment in Lyon (France), where artificial recharge operations and natural hydrological events provide independent constraints on subsurface water storage. We compare the inferred attenuation variations with complementary hydrological and geophysical observations, including rainfall records, infiltration basin water levels, piezometric measurements, and seismic velocity changes derived from autocorrelation of train signals. The results reveal consistent temporal relationships between attenuation variations and groundwater system responses, highlighting the sensitivity of attenuation-based observables to hydrological processes.

Our findings demonstrate that repetitive anthropogenic seismic sources can be used as opportunistic source for monitoring seismic attenuation variations. This passive approach offers new perspectives for continuous monitoring of groundwater dynamics in urban environments. More generally, the methodology can be extended to other sites where stable anthropogenic seismic sources are available, opening new opportunities for investigating near-surface processes using attenuation-based seismic observables.