Kinematics and geological constraints of the slow-moving Pisciotta rock slide (southern Italy)

Abstract

The Pisciotta landslide is a slow-moving deep-seated rock slide in the Campania region of southern Italy, which has damaged a provincial road several times in the last decades and currently poses a hazard to the national railway that intersects the toe of the landslide. The landslide involves an Oligocene turbidite series, which is composed of intercalated calcarenites, marls and mudrocks.The principal objectives of this study were to investigate the morphological evolution of the unstable slope, quantitatively analyse ground deformations and construct an engineering-geological model that is consistent with the spatial features of the landslide. The long-term evolution of the unstable slope was assessed through the examination of available aerial photos from 1943 to 2006. Kinematic analyses of the ground deformations were conducted based on observed progressive displacement of the road, as evident from the topographic maps and orthophotos (1955–2006), and the bi-weekly displacement survey of 50 targets distributed across the landslide area (September 2006–March 2009). The engineering-geological model of the landslide was reconstructed from the stratigraphic data obtained from the study of borehole data and monitoring of inclinometers as well as from geological, structural and geophysical surveys. The analysis of the aerial photographs revealed an early stage of deformation in 1943, which has been gradually widening since then. In addition to the main scarp and the landslide flanks, other significant landslide structures such as the longitudinal and transverse cracks as well as the positive or negative morphologies were monitored and mapped in the subsequent years. These studies indicated a progressive erosion of the upper part of the slope and a bulging of the foot. Long-term kinematic analysis based on the progressive displacements of the road allowed the measurement of the ground deformations from 1955 to 2009, which revealed a cumulative horizontal displacement of up to 53m and an average velocity of 0.98myear−1, which has increased in the recent decades. In addition, the recent monitoring of the ground deformations demonstrated a continuous activity with an approximately constant rate of displacement and a composite kinematic history of the landslide body through differential displacements and associated velocities. The engineering-geological model of the landslide was found to be controlled by specific stratigraphic and structural constraints. The landslide involves a stratigraphic interval of the Saraceno Formation (Nord-Calabrese tectonic unit) with a largely marly–argillaceous composition whose structural setting displays complex folding (at the mesoscale) and faulting with an approximately monocline attitude of bedding and a downslope dip direction at the macroscale. The left flank of the landslide rests on a normal fault.