Giovanni Toscani

Plio-Quaternary tectonic evolution of the Northern Apennines thrust fronts (Bologna-Ferrara section, Italy): seismotectonic implications

The outermost, NE-verging fronts of the Northern Apennines (Italy) are overlain by a thick syntectonic sedimentary wedge filling up the basin beneath the Po Plain. Due to fast sedimentation rates and comparatively low tectonic rates, the fronts are generally buried. Evidence for their activity includes scattered historical and instrumental earthquakes and drainage anomalies controlled by growing buried anticlines. The largest earthquakes, up to M w 5.8, are associated with active compression, with a GPS-documented shortening rate <1 mm/a. We used geological, structural and morphotectonic data to draw a N-S-striking section between Bologna and Ferrara, aimed at analyzing whether and how the deformation is partitioned among the frontal thrusts of the Northern Apennines and identifying the potential sources of damaging earthquakes. We pointed out active anticlines based on the correspondence among drainage anomalies, historical seismicity and buried ramps. We also analyzed the evolution of the Plio-Quaternary deformation by modeling in a sandbox the geometry, kinematics and growth patterns of the thrust fronts. Our results (i) confirm that some of the main Quaternary thrusts are still active and (ii) highlight the partitioning of deformation in the overlap zones. We note that the extent and location of some of the active thrusts are compatible with the location and size of the main historical earthquakes and discuss the hypothesis that they may correspond to their causative seismogenic faults.

Analogue modeling of positive inversion tectonics along differently oriented pre-thrusting normal faults: An application to the Central-Northern Apennines of Italy

Inversion tectonics represent a key process in many orogens worldwide. The related mechanisms of fault reactivation and the effects of an articulated preshortening setting on thrust and fold development are still challenging questions. Modes and geometries of inversion have been the object of several analogue models. In this work, we analyzed the influence of an articulated high-angle preexisting discontinuity in the development of thrusts using sandbox modeling. The model geometry is based on the architecture of the major faults in the Central-Northern Apennines of Italy, where differently oriented Mesozoic–Cenozoic inherited extensional structures are clearly detectable and display contrasting styles of positive inversion tectonics. Quartz-sand is the analogue material adopted to model Mesozoic–Cenozoic sedimentary successions, and glass microbeads represent preexisting fault rocks. The geometry of the segmented preexisting structure is composed of two segments with the same dip (∼60°): one oblique and another orthogonal to the shortening direction. Our results show that different styles of positive inversion tectonics can coexist and that the obliquity angle between inherited structures and the shortening direction is a leading factor controlling the degree of inversion: The oblique segment of the discontinuity exhibits a complete reactivation, whereas along the orthogonal segment, shortcut is the prevalent mechanism. The oblique element, moreover, represents a cross-strike discontinuity that guides the localization and curved geometry of the thrusts, compartmentalizing the deformation. Our findings can be applied to fold-and-thrust belts characterized by the presence of cross-strike discontinuities.

Reconciling deep seismogenic and shallow active faults through analogue modelling: the case of the Messina Straits (southern Italy)

Abstract: The catastrophic 28 December 1908, Mw 7.1, Messina Straits earthquake was generated by a large, low-angle, SE-dipping, blind normal fault. A number of shallow, high-angle normal faults arranged in a graben-like fashion occur in the same area both on land and offshore, reaching the surface and in some instances affecting recent deposits. These faults are normally interpreted as active and have often been considered potentially seismogenic. We used an analogue modelling approach to simulate the evolution of a large, low-angle normal fault and investigate its relationships with the overlying secondary faults. We find that these faults represent the brittle surface expression of the long-term activity of the underlying master fault, and that all faults mapped by previous workers in the Messina Straits are compatible with sustained slip along the fault responsible for the 1908 earthquake. Our results confirm that analogue modelling provides a useful tool to investigate the evolution and the hierarchical relationships of fault systems, suggesting that this approach is effective in the investigation of complex seismogenic areas.

Fracture patterns evolution in sandbox fault-related anticlines

Timing and distribution of fractures related to folding is a crucial topic for migration and accumulation of hydrocarbons in structural traps. We performed sandbox analogue models to investigate the fracture patterns evolution in fault-related anticlines, e.g. fault-propagation and fault-bend fold. Analogue models allow us to: ( i ) reproduce geometry and kinematics of different kinds of folds, and ( ii ) describe and quantify fractures through time in all deformation stages. Three-dimensional digital model reconstructions facilitate the comparison of different steps in the evolution of fault-related anticlines and to highlight similarities and differences in fractures development. Quantitative parameters of fractures as orientation, number and average length have been acquired in each step of deformation using an automated procedure. The fault-related anticline models show that fractures development evolves with a cyclic and non-linear trend, depending on the geometry and kinematic of anticlines. We validate our approach by comparing experimental results with natural cases. Our methodology combined with other studies such as seismic surveys, field analyses and boreholes data may contribute to understanding the nature of fracture networks in real fault-related anticlines, identifying uncertainties and helping to reduce risks during exploration and drilling activities.

The Friulian-Venetian Basin II: paleogeographic evolution and subsidence analysis from micropaleontological constraints

During the Cenozoic, the Friulian-Venetian Basin (FVB, NE Italy) underwent a complex evolution, related to the inherited Mesozoic sea-bottom topography and the load exerted by the main tectonic phases which affected the three surrounding belts: the Dinarides to the east, the Southern Alps to the north and the Northern Apennines to the south-west. The study of the foraminiferal assemblages from over 500 samples collected from 13 key wells provides important constraints on the paleobathymetric changes which occurred into the basin through time. Moreover, the defined bathymetric ranges, together with information on both thickness of the different depositional units and depositional geometries (derived from 2D seismic), were used as input in geohistory analysis in order to reconstruct the subsidence/uplift trends occurred in different sectors of the basin, as a response to collisional tectonics acting along basin boundaries. The collected results show that the overall depositional architecture of the FVB is the result of six main tectono-depositional phases (Lutetian, Chattian, Langhian, Tortonian, Piacenzian and Quaternary) characterised by paleobathymetric variations and subsidence/uplift trends reflecting the change in the tectonic control of the basin and the balance between subsidence and sediment supply. In particular, the easternmost sector of the FVB evolved as a Dinaric foredeep during Lutetian time. Since Chattian time (Cavanella Group), a moderate subsidence phase characterised by faint flexure to the north occurred, which was followed by a Langhian accentuated subsidence phase, consistent with the development of a Southalpine system. The accommodation space was progressively outpaced by the sediment flux during Serravallian-Messinian time as demonstrated by an overall shallowing upward trend recorded in this stratigraphic interval. A new basin configuration occurred during Piacenzian, when a complex geometry was developed due to the concurrent flexural load of the Southern Alps, to the North, and of the Apennines, to the South. Unlike the previous stratigraphic intervals, the Quaternary sedimentary sequence eventually shows a broadly symmetrical geometry with fast and relatively homogeneous subsidence all over the basin, overbalanced by the sedimentary supply. The observed symmetrical subsidence distribution could be interpreted as a consequence of both vanishing tectonic control and increase of sedimentary input related to increasing climatic variability.