http://hdl.handle.net/2122/208 2013-05-26T05:39:32Z http://hdl.handle.net/2122/8056 Title: Upper mantle structure below the European continent: Constraints from surface-wave tomography and GRACE satellite gravity data Authors: Tondi, R.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Schivardi, R.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Molinari, I.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Morelli, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia Abstract: We here exploit fundamental mode Rayleigh and Love seismic wave information and the high resolution satellite global gravity model GGM02C to obtain a 1° × 1° 3-D image of: (a) upper-mantle isotropic shear-wave speeds; (b) densities; and (c) density-vS coupling below the European plate (20°N–90°N) (40°W–70°E). The 3-D image of the density-vS coupling provides unprecedented detail of information on the compositional and thermal contributions to density structures. The accurate and high-resolution crustal model allows us to compute a reliable residual topography to understand the dynamic implications of our models. The correlation between residual topography and mantle residual gravity anomalies defines three large-scale regions where upper mantle dynamics produce surface expression: the East European Craton; the eastern side of the Arabian Plate; and the Mediterranean Basin. The effects of mantle convection are also clearly visible at: (1) the Eastern Sirt Embayment; (2) the West African Craton northern margins; (3) the volcanically active region of the Canarian Archipelago; (4) the northern edge of the Central European Volcanic Province; and (5) the Northeastern part of the Atlantic Ocean, between Greenland and Iceland. Strong connections are observed among areas of weak radial anisotropy and areas where the mantle dynamics show surface expression. Although both thermal and additional dependencies have been incorporated into the density model, convective down-welling in the mantle below the East European Craton is required to explain the strong correlation between the estimated negative mantle residual anomalies and the negative residual topography. 2012-09-04T22:00:00Z http://hdl.handle.net/2122/7706 Title: Convective support of long-wavelength topography in the Apennines (Italy) Authors: D'Agostino, N.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; McKenzie, D.; Bullard Laboratories, University of Cambridge Abstract: Two different free-air gravity datasets from the Apennines have been analysed in the frequency domain to investigate the mechanisms of support of topography. At short wavelength (λ<150 km) the best fit between the observed and the calculated admittance gives a value of the elastic thickness of 3.7 km. The observed behaviour of the admittance at larger wavelengths (λ>150 km) shows that such topography is not supported by elastic stresses in the lithosphere but is dynamically supported by mantle convection. The distribution of gravity anomalies and topography suggests that the mantle is rising beneath the main topographic bulge of the Apennines and that this flow is maintained by buoyancy forces, rather than being driven by movement of the subducted slab. 1999-09-30T22:00:00Z http://hdl.handle.net/2122/5383 Title: Il contributo dei pozzi perforati dalla Regione Lombardia alla conoscenza del Pleistocene lombardo Authors: Scardia, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Milano-Pavia, Milano, Italia; Muttoni, G.; Università di Milano Abstract: Facies analysis applied to several up to 220-m-deep cores, taken by Regione Lombardia in the central-northern Po Plain, allowed to recognize an overall regressive sequence consisting of cyclotemic shallow marine and fluvial-deltaic deposits overlain by distal to proximal braidplain sediments. Magnetostratigraphy, coupled with calcareous nannoplankton biostratigraphy, was used to date marine and fluvial-deltaic sediments to the early Pleistocene and continental sediments to the middle–late Pleistocene. Sediment accumulation rates were of ~0.3-0.4 mm/yr in the early Pleistocene, whereas an overall reduction in sediment accumulation rates to ~0.06-0.08 mm/yr, associated to relevant unconformities, characterized the middle-late Pleistocene. Stratigraphic evidences from petrographic, sedimentologic and palynologic analyses highlight in the Regione Lombardia cores a drastic reorganization of vegetational, fluvial, and Alpine drainage patterns, associated to a sequence boundary termed the “R surface”. The “R surface”, seismically traceable across the Po Plain subsurface, was constrained magnetostratigraphically to the first prominent Pleistocene glacio-eustatic lowstand of marine isotope stage (MIS) 22 at 0.87 Ma at the end of the Mid-Pleistocene Revolution, when climate worsened globally and locally caused the onset of the first major Pleistocene glaciation in the Alps. Most marine deposits in the cores lie above sea level highstands of corresponding age, suggesting that they have been uplifted. In order to estimate the observed rock uplift, sediments were back-stripped to elevations at times of deposition (expressed in meters above current sea level) by applying a simple Airy compensation model. The correlation of the isostatically corrected sedimentary facies to a glacio-eustatic reference curve obtained from classic oxygen isotope studies highlights a positive elevation mismatch (rock uplift) in the range of 70-120 m, which occurred after the onset of the major Pleistocene glacial-interglacial cycles at rates of at least 0.15-0.09 mm/yr. Although the driving forces of the observed rock uplift cannot be unambiguously identified, but its timing of onset after the beginning of the major Pleistocene glacial-interglacial cycles and the low seismicity observed in the most of the Regione Lombardia area seem to point to an isostatic readjustment of the chain probably due to the long-term erosional removal of sediments during major Pleistocene glacial advances. 2008-12-31T23:00:00Z http://hdl.handle.net/2122/4932 Title: Determining the optimal Bouguer density for a gravity data-set Authors: Cocchi, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Graziano, F.; Caratori Tontini, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Carmisciano, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia Abstract: Two methods are commonly adopted to evaluate the optimal Bouguer density for a given data-set, starting from different data characteristics or geological regime, giving in many cases different results. We propose some simple extension of these methods in order to make their results compatible. To this aim, we have used free-air gravity satellite data from Geosat and ERS-1 missions in order to compile a Bouguer gravity map of the Mediterranean Sea. The complete Bouguer correction has been applied by using the method of Parker (1972), that acts in the Fourier domain and allows for an exact evaluation of the gravity contribution from an highly sampled topographic model of the land. The density used for the Bouguer reduction has been obtained thus from the gravity data-set itself, by using two different optimization methods that have given the same optimal result of 2400 kg/m3. We have studied the radial power spectrum of the data, choosing the optimal Bouguer density as the one that minimizes its slope, i.e. the fractal dimension of the resulting gravity map in the band of wavelength from 45 km to 105 km. The second approach consists of studying the correlation between topography and Bouguer anomaly by spatial crossplots for a significant sub-set of the data. In the past these methodologies were applied alternatively since they gave different optimization values, especially the second method that seems to ignore large-wavelength isostatic effects. The main novelty of our work is represented by the combined application of both the approaches having as common goal the reduction of the short-wavelength effects of topography in the gravity map. Actually we have revisited both the methodologies, proposing slight modifications to make their efforts compatible. Their coincident results confirm their validity of application and give reliability to the recovered value of the Bouguer optimal density. As a first result we have obtained a revised Bouguer map for the Mediterranean Sea, that is useful for large-scale geological studies. Moreover, studying the correlation between Bouguer anomaly and bathymetry, we propose the compilation of a new interpretative tool that may be considered a sort of normalized correlation map defining the 2D isostatic setting of the investigated region, without introducing any lithospheric model. In a direct way we have found that the over-all region seems to be in a complete isostatic equilibrium apart from the young basins of Tyrrhenian Sea and Aegean Sea, confirming previous similar results. 2007-05-21T22:00:00Z http://hdl.handle.net/2122/4366 Title: Post glacial readjustment, sea level variations, subsidence and erosion along the Italian coasts Authors: Stocchi, P.; DEOS, Faculty of Aerospace Engineering, Delft University of Technology,; Girometti, L.; Istituto di Fisica, Universita` di Urbino “Carlo Bo”, Urbino, Italy; Spada, G.; Istituto di Fisica, Universita` di Urbino “Carlo Bo”, Urbino, Italy; Anzidei, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia Abstract: Ongoing sea level variations and vertical land movements measured by tide gauges and continuous GPS stations along the Italian coasts stem from several factors acting on different spatiotemporal scales. Conversely to tectonics and anthropogenic effects, which are characterized by a heterogeneous signal, the adjustment of solid Earth and geoid to the melting of the late– Pleistocene ice sheets results in a smooth long–wavelength pattern of sea level variation and vertical deformation across the Mediterranean, mostly driven by the melt water load added to the basin. In this work we define upper and lower bounds of the effects of glacial isostatic adjustment (GIA) on current sea level variations and vertical ground movements along the coasts of Italy. For plausible mantle viscosity profiles we explore to what extent the spatial variability of observed rates may be attributed to delayed isostatic recovery of both solid Earth and geoid. In addition, we show that long–wavelength patterns of sea level change are tuned by the effects of GIA, and that coastal retreat in Italy is broadly correlated with the expected ongoing rates of post–glacial sea level variations. 2007-12-31T23:00:00Z http://hdl.handle.net/2122/2070 Title: Determining the optimal Bouguer density for a gravity data set: implications for the isostatic setting of the Mediterranean Sea Authors: Caratori Tontini, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Graziano, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Cocchi, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Carmisciano, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Stefanelli, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia Abstract: We have used free-air gravity satellite data from GEOSAT and ERS-1 missions to compile a Bouguer gravity map of the Mediterranean Sea. The complete Bouguer correction has been applied by using the method of Parker, that acts in the Fourier domain and permits the exact evaluation of the gravity contribution from an highly sampled topographic model of the land. The density used for the Bouguer reduction has been obtained from the gravity data set itself, by using two different optimization methods that have given the same optimal result of 2400 kgm−3. We have studied the radial power spectrum of the data, choosing the optimal Bouguer density from its slope, as the one which minimizes the fractal dimension of the resulting gravity map. The second approach consists of studying the correlation between topography and Bouguer anomaly by spatial cross-plots for a significant subset of the data. Both these approaches are aimed at reducing the short-wavelength effects of topography in the gravity map, but in the past they have been traditionally used alternatively since they gave different optimization values, especially the second method that seems to ignore large-wavelength isostatic effects. Actually, we have revisited both the methodologies, proposing slight modifications to make their efforts compatible. Their coincident results confirmtheir validity of application and give reliability to the recovered value of the Bouguer optimal density. Moreover, modifying the second approach allows us to compile a sort of normalized correlation map, which we propose in this paper, defining the 2-D isostatic setting of the investigated region without introducing any further lithospheric model. The final result is a revised Bouguer map compiled using a grid with a resolution of 2 min, that is useful for large-scale geological studies and gives important information about the compensation mechanism of the Mediterranean Sea: in a direct way we have found that the overall region seems to be in a complete isostatic equilibrium apart from the young basins of Tyrrhenian Sea and Aegean Sea, confirming previous similar results. 2006-12-31T23:00:00Z