The 27 February 2014 San Leo landslide (northern Italy)

Abstract

The report describes a recent landslide occurred in San Leo (northern Italy), an outstanding village from the historical, architectural and landscape point of view. On February 27, 2014, around 6 pm local time, about 0.30 Mm3 of rock detached from a sub-vertical cliff and fell into the facing valley, producing a roar and a shake, which was initially perceived by the inhabitants as an earthquake, then followed by a dust cloud produced by the fragmentation of material during the collapse. Fortunately, nobody was injured, neither the landslide damaged any relevant structure; anyhow, it is still posing a severe threat to the village and, above all, to the fortress that represents an architectural masterpiece dating back to the middle ages. An outlook of the event will be given, along with the description of the peculiar geological and geomorphological features driving the slope instability phenomena, which indeed are widely diffused in the entire region. Lastly, an overview of the landslides, which historically affected the village, is also given, showing how natural hazards can influence the history of a site

Back Analysis of the 2014 San Leo Landslide Using Combined Terrestrial Laser Scanning and 3D Distinct Element Modelling

“…In fact, the comparison between the measured P 21 before and after the failure shows a small increase, indicating the creation of new fractures during the failure. These hypotheses are in agreement with the landslide reconstruction proposed in Borgatti et al (2015). Therefore, the landslide displayed a complex style of activity, and can be described as a rock slide-rock topple.…”

A Preliminary Investigation on the Role of Brittle Fracture in the Kinematics of the 2014 San Leo Landslide

“…The town is located on top of a 120 m thick rocky plateau, comprising sandstone and limestone overlying a soft, marine clay shale that extends throughout the Val Marecchia region. On the afternoon of 27th February 2014, a 300,000 m 3 landslide detached from the north-eastern flank of the plateau, toppling and fragmenting at the base of the slope [45]. The failure involved the detachment of a 200 m wide slab of rock mass and resulted in a retrogression of about 30 m of the edge of the plateau (Figure 1b).…”

“…The failure involved the detachment of a 200 m wide slab of rock mass and resulted in a retrogression of about 30 m of the edge of the plateau (Figure 1b). The landslide transitioned into a rock and debris avalanche that crossed the Campone gully at the base of the slope and climbed the opposite valley side by about 30 m. The undrained load induced on the underlying clay-rich materials also caused the activation of an earthflow that started to move with a velocity of 30 cm/day [45]. The slope failure generated a seismic wave that was felt by the local population and recorded by the Mount Carpegna seismic station, managed by INGV (the Italian National Institute for Geophysics and Volcanology) [45].…”

“…The landslide transitioned into a rock and debris avalanche that crossed the Campone gully at the base of the slope and climbed the opposite valley side by about 30 m. The undrained load induced on the underlying clay-rich materials also caused the activation of an earthflow that started to move with a velocity of 30 cm/day [45]. The slope failure generated a seismic wave that was felt by the local population and recorded by the Mount Carpegna seismic station, managed by INGV (the Italian National Institute for Geophysics and Volcanology) [45]. Based on eye-witness reports and seismographic data, the event was estimated to have occurred over a time frame of 150 s. The seismograph log, in particular, shows two marked peaks in ground acceleration, suggesting that the failure may have occurred in two stages: the first involving the detachment of the slab, and the second coinciding with the toppling and the following impact of the debris onto the valley bottom [45].…”

“…The slope failure generated a seismic wave that was felt by the local population and recorded by the Mount Carpegna seismic station, managed by INGV (the Italian National Institute for Geophysics and Volcanology) [45]. Based on eye-witness reports and seismographic data, the event was estimated to have occurred over a time frame of 150 s. The seismograph log, in particular, shows two marked peaks in ground acceleration, suggesting that the failure may have occurred in two stages: the first involving the detachment of the slab, and the second coinciding with the toppling and the following impact of the debris onto the valley bottom [45].…”