Fig. 1: Spriana rockslide.

a Location map; b geological and hydrogeological model, with basal shear zone sampling locations, sample numbers and location of field measuring devices used for the analysis. The representation of the perched aquifer integrates borehole and piezometer observations made upon 1989–90 site investigations. Horizontal and vertical distance are same scaling; c monitoring time series of rockslide surface displacement (wire extensometer) and groundwater level (hydraulic borehole piezometer), with selected rockslide acceleration periods outlined; d detail of acceleration impulse associated to a period of increase of groundwater level (acceleration period n.1) and characteristic descriptors: time to peak, peak velocity, long-term velocity.