Advancing Seismic Slope Instability Monitoring: Integrating Fibre-Optic and Nodal Array Sensing

Slope instabilities pose serious risks to infrastructure and communities in mountainous regions. Understanding their internal structure and time-dependent dynamics is vital for effective hazard assessment and mitigation. The Cuolm da Vi instability in central Switzerland, one of the largest slow-moving instabilities in the Alps, offers an ideal setting for field-based slope instability research. We present the motivation, design, and implementation of a novel large-scale multi-sensor seismic network to study the subsurface structure and deformation dynamics of Cuolm da Vi across an unprecedented range of spatial and temporal scales: from decimetres to kilometres and milliseconds to years. The sensor network includes a hexagonal grid of more than 1,000 seismic nodes primarily deployed for high-resolution 3D characterization. This temporary nodal array was complemented with a trenched 6.5km fibre-optic configuration, which covers the most unstable parts of Cuolm da Vi using a multi-directional cable layout, suited for Distributed Acoustic and Strain Sensing measurements (DAS & DSS). Data acquisition spanned two years so far, including controlled-source experiments and continuous seismic and strain sensing campaigns. Initial data screening demonstrates the network's potential to facilitate imaging of the internal structure and monitoring of seasonal subsurface instability processes. Our study shows the feasibility of dense long-term seismic monitoring in challenging Alpine terrain using nodal and distributed fibre-optic sensing techniques, opening new opportunities for slope instability research and hazard assessment.