Michele M. C. Carafa

Abstract: The study of geodynamics relies on an understanding of the strength of the lithosphere. However, our knowledge of kilometer-scale rheology has generally been obtained from centimeter-sized laboratory samples or from microstructural studies of naturally deformed rocks. In this study, we present a method that allows rheological examination at a larger scale. Utilizing forward numerical modeling, we simulated lithospheric deformation as a function of heat flow and rheological parameters and computed several testable predictions including horizontal velocities, stress directions, and the tectonic regime. To select the best solutions, we compared the model predictions with experimental data. We applied this method in Italy and found that the rheology shows significant variations at small distances. The strength ranged from 0.6 +/- 0.2 TN/m within the Apennines belt to 21 +/- 6 TN/m in the external Adriatic thrust. These strength values correspond to an aseismic mantle in the upper plate and to a strong mantle within the Adriatic lithosphere. With respect to the internal thrust, we found that strike-slip or transpressive, but not compressive, earthquakes can occur along the deeper portion of the thrust. The differences in the lithospheric strength are greater than our estimated uncertainties and occur across the Adriatic subduction margin. Using the proposed method, the lithospheric strength can be also determined when information at depth is scarce but sufficient surface data are available. Citation: Carafa, M. M. C., and S. Barba (2011), Determining rheology from deformation data: The case of central Italy, Tectonics, 30, TC2003, doi: 10.1029/2010TC002680.

Abstract: Two critical items in the energetic budget of a seismic province are the strain rate, which is measured geodetically on the Earth's surface, and the yearly number of earthquakes exceeding a given magnitude. Our study is based on one of the most complete and recent seismic catalogs of Italian earthquakes and on the strain rate map implied by a multiyear velocity solution for permanent GPS stations. For each of 36 homogeneous seismic zones we use the appropriate Gutenberg-Richter relation, which is based on the seismicity catalog, to estimate a seismic strain rate, which is the strain rate associated with the mechanical work due to a coseismic displacement. We show that for each seismic zone, the volume storing most of the elastic energy associated with the long-term deformation, and hence the seismic strain rate, is inversely proportional to the static stress drop. The GPS-derived strain rate for each seismic zone limits the corresponding seismic strain rate, and an upper bound for the average stress drop is estimated. We show that the implied regional static stress drop varies from 0.1 to 5.7 MPa for catalog earthquakes in the moment magnitude range [4.5-7.3]. The stress drop results are independent of the regional a and b parameters and heat flow but are very sensitive to the assumed maximum magnitude of a seismic province. The data do not rule out the hypothesis that the stress drop positively correlates with the time elapsed after the largest earthquake recorded in each seismic zone.

Abstract: The present-day tectonic setting of the Italian peninsula is very complex and involves competing geodynamic processes. In this context, southern peninsular Italy is characterised by extension along the Apenninic belt and in the Tyrrhenian margin and by transpression in the Apulia-Gargano region. The extension is well defined by means of geological, seismological, and contemporary stress data. For the latter only few data are available in the Apulia-Gargano region, leaving the state of stress in that area unresolved. Here we develop a finite-element model of the southern Italian region in order to predict the contemporary stress field. Our model predictions are constrained by model-independent observations of the orientation of maximum horizontal stress (S-Hmax), the tectonic regime, and the horizontal velocities derived from GPS observations. We performed a blind test with 31 newly acquired S-Hmax orientations in the Southern Apennines. These new data come from the analysis of orehole breakouts performed in 46 deep oil exploration wells ranging in depth from 1300 to 5500 m. The model results agree with the stress data that define a prevailing NW-SE S-Hmax orientation along the Apenninic belt and foredeep and thus are capable to predict the stress field where no stress information is available. We first analyse how much model predictions, based on older data, deviate from present-day stress data and then recalibrate the models based on our new stress data, giving insight into the resolution of both models and data. In the studied region, which is affected by low deformation rates, we find that geodetic data alone cannot resolve such low levels of deformation due to the high relative measurement errors. We conclude that both GPS and stress data are required to constrain model results. (C) 2009 Elsevier B.V. All rights reserved.

Abstract: What forces control active deformation in the Central Mediterranean? Slab-pull has long been debated, but no other hypothesis has been generally accepted. Here we analyze the role of shear basal tractions. By using a thin-shell modeling technique, we generated a large number of models that span different sets of boundary conditions from the literature; we then explored acceptable ranges of model parameters. We computed residuals between model predictions and several datasets of stress directions, GPS measurements and tectonic stress regimes that have been produced in recent studies, and then compared the best models obtained in the presence of tractions with those obtained in the absence of tractions. For all tested boundary conditions and all considered datasets, our results show that the only successful models are those with significant basal shear traction exerted by eastward mantle flow.