Tectonic control on the development and distribution of large landslides in the Northern Apennines (Italy)

- The relationships between large complex landslides and tectonic structures are examined.
- Landslides develop along lines of weakness and failure surfaces caused by tectonics.
- Tectonics cause topographic growth and over-steepening of the slopes.
- Tectonics exert an active and passive role on landslide distribution and type.
- Landslides may be an indicator of regional-scale, well-constrained tectonic processes.

The causes of landslides generally invoked in the Northern Apennines of Italy do not fully explain some observed oriented distributions of large landslides along regional-scale tectonic structures (late orogenic antiforms). The aim of the work is to deeply explore the role of tectonics in controlling the development and arrangement of large landslides. We employed a multidisciplinary approach which took into account geomorphological and geological field data, topographic analysis and deep seismic reflection profiles integrated with previously published apatite fission track cooling ages, shallow geophysical and GPS data. In order to explore these relationships, the Valmozzola area was selected as suitable case study, owing to the presence of clearly expressed relationships between recent extensional faults and related fractures and elements of active landslides. Moreover, in the Valmozzola area contractional tectonics acted to produce rock uplift and thus topographic growth. These processes caused hillslopes to approach their threshold angle, and promoted landslides triggered mainly by climate factors. The geological and geomorphological features characterizing the Valmozzola case study affect the entire study area, as they evolved during the same tectonic and climatic phases that characterized this part of the Northern Apennines. Therefore, the results from the Valmozzola area act as a proxy to constrain the control exerted by tectonics on large landslides across a wider area. The distribution of the large landslides has been controlled by tectonics which determined lines of weakness and failure surfaces (passive role) affecting the slopes. On the other hand, tectonics also caused the topographic growth and over-steepening of the slopes (active role) that promoted the occurrence of large landslides. The distribution of large landslides may, therefore, highlight the existence of tectonic processes and it may be used as an indicator of regional-scale tectonic activity, once the geological and geomorphological framework is well constrained.