In this work we built a three-dimensional geometrical model of a sector of the Ferrara-Romagna fold and thrust system buried under the Plio-Pleistocene sediments of the Po Plain in order to model numerically the active stress field of the region. The geometrical model was built using the commercial software Petrel 2009 (Schlumberger). The input data include: 1. the Digital Elevation Model (DEM) of the topography surface; 2. the grid of the Plio-Pleistocene base; 3. the grid of the Cretaceous top, realized by digitizing the map published by CASERO et alii (1990); 4. the composite seismogenic sources of the Database of Seismogenic Sources (DISS) version 3.1.0; 5. some geological sections reported in the literature (BOCCALETTI et alii, 2003; FANTONI & FRANCIOSI, 2009; PIERI & GROPPI, 1981). Once collected, these data were imported into Petrel, using the following procedure. Originally, the DEM, grid horizons and DISS seismogenic sources have been imported as points defined by three coordinate values (Easting, Northing and depth). Later, these data were converted from points to surfaces. The geological sections have been imported to control the geometry of horizons and faults. Both faults and horizons were adjusted to make them coherent with the sections. The main tectonic elements in the model consist of a set of ramps that converge downward to the main detachment likely located within the Upper Triassic units. Afterwards this geometry was imported in Visage for the numerical modelling. A 3D model has been realised to simulate the present-day stress field of the Northern Apennines frontal thrust system. An elasto-plastic rheology was adopted for the modelling using the Mohr-Coulomb failure criterion. Geomechanical properties for each formation and faults comprised Young's modulus, Poisson's ratio, density, frictional angle, cohesion and they were assumed on the basis of published geological data. The models were performed in three steps with different boundary conditions. In the first step we simulated the lithostatic stress (Sv), obtaining a model in equilibrium with gravity. The side boundaries were constrained horizzontally. Afterwards, loads were added to simulate a regional stress state comprising the tectonic loading component (SH and Sh). However, to evaluate the validity of the results, the model solutions were compared with the map of the active stress field and with the data of seismicity in the same area. In the last step of the simulation (tectonic phase) we forced the models with a 1 meter displacement (applied onto the SW lateral boundary) directed toward NE, simulating the shortening occurring in the region in 1000 years, according the present-day plate kinematics of the Northern Apennines region. The tectonic displacement was applied by 0.1 step increments to evaluate the change of the mechanical properties along the principal tectonic features.
Three-dimensional geological and geomechanical modeling of the Northern Apennine front in the Po Plain
MICHELE LIVANI;DAVIDE SCROCCA;
2010
Abstract
In this work we built a three-dimensional geometrical model of a sector of the Ferrara-Romagna fold and thrust system buried under the Plio-Pleistocene sediments of the Po Plain in order to model numerically the active stress field of the region. The geometrical model was built using the commercial software Petrel 2009 (Schlumberger). The input data include: 1. the Digital Elevation Model (DEM) of the topography surface; 2. the grid of the Plio-Pleistocene base; 3. the grid of the Cretaceous top, realized by digitizing the map published by CASERO et alii (1990); 4. the composite seismogenic sources of the Database of Seismogenic Sources (DISS) version 3.1.0; 5. some geological sections reported in the literature (BOCCALETTI et alii, 2003; FANTONI & FRANCIOSI, 2009; PIERI & GROPPI, 1981). Once collected, these data were imported into Petrel, using the following procedure. Originally, the DEM, grid horizons and DISS seismogenic sources have been imported as points defined by three coordinate values (Easting, Northing and depth). Later, these data were converted from points to surfaces. The geological sections have been imported to control the geometry of horizons and faults. Both faults and horizons were adjusted to make them coherent with the sections. The main tectonic elements in the model consist of a set of ramps that converge downward to the main detachment likely located within the Upper Triassic units. Afterwards this geometry was imported in Visage for the numerical modelling. A 3D model has been realised to simulate the present-day stress field of the Northern Apennines frontal thrust system. An elasto-plastic rheology was adopted for the modelling using the Mohr-Coulomb failure criterion. Geomechanical properties for each formation and faults comprised Young's modulus, Poisson's ratio, density, frictional angle, cohesion and they were assumed on the basis of published geological data. The models were performed in three steps with different boundary conditions. In the first step we simulated the lithostatic stress (Sv), obtaining a model in equilibrium with gravity. The side boundaries were constrained horizzontally. Afterwards, loads were added to simulate a regional stress state comprising the tectonic loading component (SH and Sh). However, to evaluate the validity of the results, the model solutions were compared with the map of the active stress field and with the data of seismicity in the same area. In the last step of the simulation (tectonic phase) we forced the models with a 1 meter displacement (applied onto the SW lateral boundary) directed toward NE, simulating the shortening occurring in the region in 1000 years, according the present-day plate kinematics of the Northern Apennines region. The tectonic displacement was applied by 0.1 step increments to evaluate the change of the mechanical properties along the principal tectonic features.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
