Contribution of Dense Seismic Arrays to the Characterization of Hydrological Dynamics in Karst Systems

A significant proportion of the world’s water resources is stored in karst regions. To develop water management strategies adapted to karst hydrosystems under conditions of global change, it is essential to consider the specific characteristics of these systems, from infiltration zones to discharge points. This requires an improved understanding of groundwater recharge, water storage within the karst reservoir, and the transfer of water toward outlets. However, the strong structural heterogeneity of karst systems poses significant challenges for imaging and monitoring groundwater flow processes. Among the well-established hydrological and geophysical methods used to study subsurface water dynamics, our project focuses on integrating innovative seismic monitoring techniques with interdisciplinary approaches within a multi-scale framework.

To address these challenges, our study investigates hydrological flows along preferential pathways within a karst environment that recharge the Lez aquifer, a critical groundwater resource supplying drinking water to approximately 340,000 inhabitants in Montpellier and its surrounding areas.

As part of the multidisciplinary PEPR OneWater K3 project, we conducted ambient seismic noise monitoring using a dense array of 100 velocimeters deployed over one month across a 200 m × 1 km area encompassing fault zones and highly localized karst features. These continuous data are used both for imaging, via seismic tomography, and for monitoring purposes. For the latter, the primary objective is to produce dynamic maps of seismic velocity variations derived from autocorrelations and cross-correlations between stations. These localized variations are then correlated with a significant rainfall event and hydrological observations. We specifically aim to derive the hydrological properties controlling a synthetic model capable of reproducing seismic velocity responses to temperature and rainfall variations, with a spatial resolution that highlights distinct geological compartments. In a second step, the seismic network is used to detect seismic noise generated by fluid transfers, particularly within the most permeable zones.

Furthermore, the deployment of broadband seismic stations over a two-year period is expected to provide valuable insights into the long-term dynamics and seasonal variability of the Lez aquifer at a larger scale.