Strong daily landslide cracking activity – Does traffic drive slope failure?

Landslide failures pose a severe threat to society, especially when valley bottoms become blocked, ponding rivers and burying critical infrastructure. The erratic and spatially distributed occurrence of those rapid mass wasting processes makes it eminent to understand major drivers and find reliable predictors that can help early warning.

Here, we present results of a systematic study on a progressively developing landslide near the town of Müsch, in one of the narrowest sections of the Ahr Valley, Germany. The slope instability had been reactivated by the 2021 summer flood and shows accelerated toppling and rotational movement at the 100 m wide front, as well as surface evidence of distributed movement in the 200 m long hinterland. Partial failure of the frontal sector had been modelled, indicating the damming of the 30 m wide valley bottom, causing rapid inundation of upstream settlements.

We analyse 2.5 years of continuous seismic data from a small geophone network. Seismic coda wave interferometry and resonance frequency analysis yields insights to cyclic and progressive rock stress evolution as well as the effect of water content at and below the surface. More than 3000 discrete crack emissions due to brittle rock mass failure were detected, located and quantified. The precise timing of the crack signals reveals a strong control of working time hours, suggesting an external anthropogenic forcing of the slope instability. We discuss the generic applicability of the multi-proxy seismic approach in light of further, post-flood reactivations of slope instabilities in the Ahr Valley and elsewhere.