Abstract The subduction of large and heterogeneous mass-transport deposits (MTDs) is discussed to modify the structure and physical state of the plate boundary and therewith exert an influence on seismicity in convergent margins. Understanding which subduction-zone architectures and structural boundary conditions favour the subduction of MTDs, primarily deposited in oceanic trenches, is therefore highly significant. We use bathymetric and seismic reflection data from modern convergent margins to show that a large landslide volume and long runout, in concert with thin trench sediments, increase the chances for an MTD to become subducted. In regions where the plate boundary develops within the upper plate or at its base (non-accretionary margins), and in little-sedimented trenches (sediment thickness <2 km), an MTD has the highest potential to become subducted, particularly when characterized by a long runout. On the contrary, in the case of a heavily sedimented trench (sediment thickness >4 km) and short runout, an MTD will only be subducted if the thickness of subducting sediments is higher than the thickness of sediments under the MTD. The results allow identification of convergent margins where MTDs are preferentially subducted and thus potentially alter plate-boundary seismicity.

The Messinian mélange of the Tertiary Piedmont Basin is the product of different but interrelated processes (tectonic, gravitational, and diapiric) that operated sequentially over a short time span (intra-Messinian time) and in a geodynamic environment (episutural basin) for which mélanges have so far been poorly described. It is composed of different mappable bodies of (non-metamorphic) mixed rocks characterized by a strong facies convergence. Their geometric and stratigraphic position, the internal organization, and the nature of the bounding surfaces allow the defining of some criteria to distinguish different units of mixed rocks (tectonically disrupted unit, gravity-driven sedimentary unit, and diapiric disrupted unit) , in each of which the role of a different prevailing mélange-forming process can be inferred. None of these processes operated in isolation. They were linked by complex and intimate mutual interactions and triggered by intra-Messinian tectonics. The latter produced self- generating processes of mélange formation in which gravitational and diapiric processes triggered and affected each other. Different pulses of overpressured fluids (often rich in methane) strongly governed sediment deformation and also played a crucial role in influencing the time relationships and causative links between the different mélange-forming processes. Faulting may have triggered gas hydrate dissociation, promoting the upward rise of overpressured fluids. These fluids reduced the shear strength of the overlying sediments, promoting large-scale gravity-driven phenomena. Loading provided by rapid emplacement of the gravity-driven sedimentary bodies could have, in turn, developed new overpressured conditions necessary to promote the upward rise of poorly consolidated sediments and shale diapirism.

The Geological-Structural Map of the Central-Southern Apennines (Italy) 1 provides entirely revised and original cartography for a large sector of the orogenic belt that stretches along peninsular Italy. New data collected by the authors over the past 20 years, together with field revisions of published data, and available subsurface data are synthesized in two geological map sheets at scale 1:250,000 giving a regional overview of the stratigraphy, geometry, and structure of the Apenninic fold-and-thrust belt. The Apennines comprise a variety of lithotectonic assemblages that evolved through interaction between the African and European plates in the central Mediterranean, with: ( i ) Mesozoic development of the Tethyan domain; ( ii ) Cretaceous-Eocene oceanic subduction; ( iii ) Oligocene-Miocene and Pliocene convergence, continental collision and shortening; and ( iv ) late Miocene–present extensional collapse of the contractional edifice. The geological maps and this paper illustrate a number of critical orogenic processes, including: (1) control of paleogeographic position and stratigraphy on the finite geometry of the thrust belt; (2) the history of progressive deformation and translation of far-traveled tectonic units; (3) selective reactivation of inherited structures during the sequence of superposed tectonic events; (4) the evolution of syntectonic and posttectonic sedimentary basins; and, (5) the propagation paths of thrust faults. The paper, together with the geological map and cross sections, provide a regional overview of the progressive tectono-stratigraphic evolution of the thrust belt, with focus on the geometry of the imbricate wedge and its subsurface geometry. Emphasis is also given to the relationships between active faulting and historical seismicity.