Exploring river dynamics through passive seismology: preliminary insights into flow and sediment transport in northern Spain

We present preliminary observations from a passive seismic monitoring programme developed within the framework of the CANALAB project, applied to fluvial systems in northern Spain. The study is based on continuous recordings in the lower Nalón River since March 2022 and, since 2025, in a headwater catchment of the Nalón basin (Aller River). Seismic stations installed close to the active channel are used to explore how ground vibrations respond to changes in river dynamics. One year of data from the Nalón site was analysed using a General Additive Model (GAM) that integrates seismic amplitude with river discharge, wind speed and a day–night component related to anthropogenic noise.

Preliminary GAM outputs indicate that river discharge explains about 92% of the variability of the seismic signal, while wind and the systemic day–night component together account for less than 2%. During the flood events of March and April 2022 and January 2023, seismic energy increased markedly between 5 and 40 Hz, which is in agreement with peak discharges and with surrogate indicators of sediment transport derived from impact plates installed on the riverbed. When only low-flow periods without detected bedload transport are considered, seismic amplitude follows an almost linear relationship with discharge, whereas during floods an excess signal appears relative to the GAM prediction, which is interpreted as being potentially related to coarse bedload transport. The new installation in 2025 in the Aller headwaters extends this framework to upstream conditions and will allow comparison between lowland and headwater responses. These observations support the potential of passive seismology as a non-invasive and continuous tool to monitor both liquid discharge and sediment dynamics, complementing conventional methods.