Arnaud Watlet, Paul Wilkinson, Jim Whiteley, Adrian White, Sebastian Uhlemann , Russell Swift, Susanne Ouellet, Minto Chris, Phil Meldrum, Lee Jones, David Gunn, Alastair Godfrey, Ben Dashwood, Roger Crickmore, Paul Clarkson, James Boyd, Jonathan Chambers

Slope failures are an ongoing global threat leading to significant numbers of fatalities and infrastructure damage. Landslide impact on communities can be reduced using efficient early warning systems to plan mitigation measures and protect elements at risk. This manuscript presents an innovative geophysical approach to monitoring landslide dynamics, which combines Electrical Resistivity Tomography (ERT) and low-frequency Distributed Acoustic Sensing (DAS), and was deployed on a slope representative of many landslides in clay rich lowland slopes. ERT is used to create detailed, dynamic moisture maps that highlight zones of moisture accumulation leading to slope instability. The link between ERT derived soil moisture and the subsequent initiation of slope deformation is confirmed by low-frequency DAS measurements, which were collocated with the ERT measurements and provide changes in strain at unprecedented spatiotemporal resolution. Auxiliary hydrological and slope displacement data support the geophysical interpretation. By revealing critical zones prone to failure, this combined ERT and DAS monitoring approach sheds new light on landslide mechanisms. This study demonstrates the advantage of including subsurface geophysical monitoring techniques to improve landslide early warning approaches, and highlights the importance of relying on observations from different sources to build effective landslide risk management strategies.