Marcello Viti

Role of kinematically induced horizontal forces in Mediterranean tectonics: insights from numerical modeling

Abstract Finite element modeling of the central–eastern Mediterranean region has been carried out to show that the recent/present deformation pattern of this zone, inferred from neotectonic observations and seismic strain rates, may be satisfactorily reproduced as effect of the relative motion of Africa and eastern Anatolia with respect to Eurasia. Numerical modeling involved 2D elastic elements in a plane-stress approximation. The model is constituted by a mosaic of poorly deformable blocks separated by much more deformable decoupling zones, representing consuming boundaries, extensional zones and transcurrent discontinuities, whose location and geometry have been deduced by neotectonic, morphological and seismological information. The calculated displacement field obtained with the modeling parametrization which allows to match the observed strain regimes is compatible with geodetic observations in the study area, but for the Hellenic Arc, where geodetic velocities are higher than those predicted by modeling. This discrepancy could be considerably reduced by adopting a higher deformability of the model in the Hellenic trench, but this condition would contrast with the Plio-Quaternary deformation pattern of the southern Aegean zone, which suggest a considerable slowdown of western Crete since the late Pliocene. Furthermore, geodetic velocities are considerably higher than the motion rates derived by moment tensor analysis in the Hellenic trench and in the internal Aegean area and cannot easily account for the low Quaternary deformation observed in the southern Aegean zone. The above discrepancy could be due to a difference between the “instantaneous” kinematic behavior of the Aegean zone, indicated by geodetic measurements, and the average behavior over longer time intervals, inferred from geological and seismological strain indicators.

Numerical simulation of the observed strain field in the central-eastern Mediterranean region

Abstract The highly heterogeneous strain field indicated by neotectonic and seismological data in the central-eastern Mediterranean region has been reproduced, at a first approximation, by finite element modelling, of a 2D elastic thin plate. The zone considered is modelled as a mosaic of poorly deformable zones decoupled by highly deformable belts, simulating the major tectonic structures indicated by geological and geophysical evidence. The deformation of the model is obtained by imposing kinematic boundary conditions, representative of the motion of Africa and eastern Anatolia relative to Eurasia. Experiments carried out with different boundary conditions and model parameterisations have provided information on the sensitivity of the model and some insights into the geodynamic behavior of the study area. The deformation pattern of the central Mediterranean area is strongly conditioned by the mechanical properties assumed in the border zones between the Aegean and Adriatic systems. The match of the complex strain pattern observed in the western Anatolian–Aegean–Balkan zones is significantly favoured if high rigidity is assigned to the inner part of this structural system. A motion of Africa with respect to Eurasia compatible with an Eulerian pole located offshore Portugal best accounts for the observed strains in the central Mediterranean region. The match of the strongly heterogeneous strain field observed in the study area can hardly be achieved by simplified models not including major tectonic features and lateral heterogeneity of mechanical properties. The kinematic field resulting from the model configuration which best simulates the observed strain field presents some differences with respect to geodetic measurements in the Aegean–Western Anatolian area, where the computed velocities are systematically lower than the geodetic ones. It is suggested that the most plausible explanation of such differences is related to the fact that the present deformation pattern, inferred from geodetic data, may be different from the middle–long term one, inferred from seismological and geological data.

Short and long term deformation patterns in the Aegean-Anatolian Systems: Insights from space geodetic data (GPS)

Geodetic measurements (GPS) in the eastern Mediterranean suggest higher rates of motion, of about 10 mm/yr, in the Aegean - Western Anatolian zone with respect to those in the central-eastern Anatolia. In this work we explore the plausibility of the hypothesis that the observed kinematics may be significantly influenced by post - seismic relaxation processes induced by the seismic activation of the North Anatolian Fault since 1939. The major implications of this hypothesis are tentatively quantified by a simplified model, constituted by an elastic lithosphere (100 km thick) coupled with a viscous asthenosphere (250 km thick with a viscosity of 10 19 Pas). The predicted perturbation of the displacement and stress fields is consistent with geodetic velocities and could also account for the major features of seismic activity in the period considered.

Recognition of periAdriatic Seismic Zones Most Prone to Next Major Earthquakes: Insights from a Deterministic Approach

The mitigation of seismic risk in Italy could be considerably helped by the recognition of the seismic zones most prone to next strong earthquake. An attempt at achieving such information has been made by considering the present knowledge about the tectonic setting in the study area and its possible connection with the spatio-temporal distribution of major historical earthquakes. The results of such investigation suggest that at present the probability of major socks is highest in the Northern Apennines.

Geodynamic/tectonic setting in the Italian Region: elements for the choiche of the reference model

The identification of a reliable geodynamic/tectonic model for the Italian region would be extremely useful for several practical purposes, in particular for quantifying the parameters to be used for seismic hazard assessment. In this work, we argue that the model presently adopted as a basis for elaborating the seismic classification of the Italian territory (MELETTI et alii, 2000) is not compatible with several major features of the observed deformation pattern and that, consequently, such choice should be reconsidered, taking into account an alternative geodynamic model that can much better explain the major tectonic events occurred in the central Mediterranean region since the late Miocene.