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The potential of long-term, real-time surface displacement monitoring by ground-based radar interferometry (GB-InSAR) to improve the understanding of mechanisms and set up objective Early Warning criteria for complex rockslides is explored. Monitoring data for a rockslide in the Central Italian Alps, collected since 1997 by ground-based and remote sensing techniques, are examined. A unique 9year continuous GB-InSAR monitoring activity supported an objective subdivision of the rockslide into "Early Warning domains" with homogeneous involved material, mechanisms and sensitivity to rainfall inputs. Distributed GB-InSAR data allowed setting up a "virtual monitoring network" by a posteriori selection of critical locations representative of Early Warning domains, for which we analysed relationships among rainfall descriptors and displacement rates. The potential of different Early Warning criteria, depending on the instability mechanisms dominating different domains, is tested. Results show that: a) rainfall Intensity-Duration-Displacement Rate relationships can be useful tools to predict displacements of "rainfall-sensitive" rockslide sectors, where clear trigger-response signals occur, but are unsuitable in rockslide domains affected by the long-term progressive failure of the rock slope; b) effective Early Warning strategies for collapse scenarios (entire rockslide, specific domains) can be enforced by modelling real-time, high-frequency GB-InSAR data according to the accelerated creep theory.

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Distributions of landslide size are hypothesized to reflect hillslope strength, and consequently weathering patterns. However, the association of weathering and critical zone architecture with mechanical strength properties of parent rock and soil are poorly-constrained. Here we use three-dimensional stability to analyze 7330 landslides in western Oregon to infer combinations of strength - friction angles and cohesion - through analysis of both failed and reconstructed landslide terrain. Under a range of conditions, our results demonstrate that the failure envelope that relates shear strength and normal stress in landslide terrain is nonlinear owing to an exchange in strength with landslide thickness. Despite the variability in material strength at large scales, the observed gradient in proportional cohesive strength with landslide thickness may serve as a proxy for subsurface weathering. We posit that the observed relationships between strength and landslide thickness are associated with the coalescence of zones of low shear strength driven by fractures and weathering, which constitutes a first-order control on the mechanical behavior of underlying soil and rock mass.

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