1,721,031 research outputs found
Seismicity of central Italy in the context of the geological history of the Umbria-Marche Apennines
No full textIn the Umbria-Marche Apennines, direct evidence of earthquakes (including data from geodetic, geophysical, historical, and paleoseismological research) is not older than 20–10 ka, but the events themselves are influenced by the whole ~250 m.y. geo- logical history of the region. For seismic sequences that have occurred in the past few decades, seismological data of increasing quality provide detailed images of the active NNW-SSE–trending normal fault systems in the upper 10 km of the crust. Major historical earthquakes and sparse paleoseismological data are also aligned parallel to the same lineaments, which clearly define the distribution of the major seismogenic sources of the region. The close connection between active tectonics and older Quater- nary faults that border a series of extensional intramountain basins is demonstrated by the fact that seismogenic and Quaternary faults are distributed along the same alignments, formed within similarly oriented stress fields, and accommodate WSW- ENE extension coherently with the active strain field. The Quaternary to present tec- tonics form part of a long-lived extensional process, active over 15–20 m.y., which is migrating eastward through time across the Italian peninsula, superimposed on the previous compressional phase that created the Apennines. The older Umbria-Marche geological history, recorded in the Triassic to Paleogene stratigraphic succession of the region, also influences the present-day distribution of seismicity. Specifically, the complex mechanical stratigraphy of the region determines the superposition of rocks with different rheological behaviors and overall thickness of the seismogenic layer. Almost all of the earthquakes occur within the sedimentary cover, with main shocks located close to the basal contact with the underlying Paleozoic basement
Fault architecture and deformation mechanisms in exhumed analogues of seismogenic carbonate-bearing thrusts
No full textMechanical heterogeneities in Umbria-Marche Apennines Thrusts: A field and experimental perspective
No full textLithological and stress anisotropy control large-scale seismic velocity variations in tight carbonates
Full text linkOur knowledge of subsurface structures often derives from seismic velocities that are measured during seismic acquisition surveys. These velocities can greatly change due to lithological, fracture frequencies and/or effective pressure/temperature variations. However, the influence of such intrinsic lithological properties and environmental conditions at the large scale is poorly understood due to the lack of comprehensive datasets. Here, we analyze 43 borehole-derived velocity datasets of 3 end-member tight carbonate sequences from Central Italy, including massive pure limestone (Calcare Massiccio, CM), thick-layered (20–50 cm) pure limestone (Maiolica, MA), and thin-layered (2–20 cm) marly limestone (Calcareous Scaglia, CS). Our results show that the main rock parameters and environmental conditions driving large scale velocity variations are bedding and paleostresses, while mineralogical composition and current tectonic stress also play a role. For each of the 3 end-members, measured VP values vary differently with depth, as the thin-layered CS units show a clear increase in Vp, while velocity slightly increases and remains constant for the thick-layered MA and massive CM units, respectively. Such observations show that velocities are affected by specific characteristics of lithological discontinuities, such as the thickness of bedding. Counterintuitively, larger Vp values were recorded in the deformed mountain range than in the undeformed foreland suggesting that higher paleo-stresses increase velocity values by enhancing diagenesis and healing of discontinuities. Our results thus demonstrate that large scale velocity variations are strictly related to variation of lithological properties and to the geological and tectonic history of an area. We suggest that such lithological and environmental controls should be taken into account when developing velocity and mechanical models for tectonically active regions of the Mediterranean Area, where earthquakes mostly nucleate and propagate through carbonate formations, and for resource exploration in fractured carbonate reservoirs
The Role of Mechanical Anisotropy in Controlling Fault Trajectories within Multilayered Carbonate and Clay-rich Rocks
No full textPleistocene calcareous tufa from the Ellera basin (Umbria, central Italy) as a key for an integrated paleoenvironmental and tectonic reconstruction
No full textContinental carbonates (calcareous tufa and associated deposits) represent a natural archive of paleoenvironmental and tectonic information that can be fully disclosed only by the application of a multidisciplinary approach. The aim of this paper is to describe the geological features of the Ellera basin (Umbria, central Italy) by integrating physical (stratigraphy, sedimentology, geochemistry, tectonics) and biological (paleontology, palynology) data. The study of the Ellera basin represents a starting point for the improvement of a methodology that could be applied to similar sedimentary systems, regardless of their actual location, extension and age.Two stratigraphic units were recognized in the Ellera basin, both characterized by multiple events of calcareous tufa deposition during the Pleistocene. In the lower San Biagio Unit, the concurrent finding of Hippopotamus (?H. antiquus) and Leptobos remains, associated with Late Villafranchian molluscs, suggests an attribution to the Early Pleistocene (Tasso or Farneta Faunal Unit, about 1.8-1.5 Ma). Both sedimentological and paleontological data indicate a periodically flooded alluvial plain depositional environment, and isotopic values of δ13C and δ18O register the establishment of a wet paleoclimate. The overlying Santa Sabina Unit lies with an angular unconformity on the San Biagio Unit, and was dated to 115,000 ± 8000 years by the application of the U-Th method. The age of the Santa Sabina Unit falls within a period of warm and humid climate (MIS 5d-e), and paleoclimatic inferences are supported by the isotopic record (δ13C and δ18O). The unit deposited in a well-vegetated fluvio-lacustrine and fluvio-palustrine environment locally dominated by herbaceous taxa, as revealed by palynological analysis.Despite the 1.5 Ma time lag between the two units, their depositional evolution shared the presence of calcareous tufa, whose deposition was controlled by similar paleoenvironmental and paleoclimatic conditions (hot and humid interglacial conditions with high rainfalls characterized both periods), as well as by the local tectonic setting and activity. In both units the maximum thickness/abundance of the calcareous tufa occurs at the intersection between two regional tectonic lineaments, controlling both the basin subsidence and the ascent of CO2-rich water. © 2012 Elsevier Ltd and INQUA
Seismic interpretation and 3D geological reconstruction of the foredeep Laga basin (Central Italy): relationships between compressive structures and extensional faults
No full textThree dimensional Gravity Local Inversion Across the Area Struck by the 2016–2017 Seismic Events in Central Italy
No full textIn this work, the crustal volume struck by the 2016–2017 seismic sequence in Central and Northern Apennines is investigated using constrained 3-D inversion of the gravity anomalies. In order to focus on the area comprising the two mainshocks of the sequence, we perform a regional field removal on the data as a preprocessing step. This residual data set is then inverted into a 3-D density contrast model. We perform a series of inversions to test different geological scenarios and parameters, with increasing complexity in the reference geometries. We first test a model comprising turbidites, carbonates and evaporites, and basement and then introduce a low-density layer at the top of the basement. The geometries are obtained in agreement with the available geological and geophysical information in the area. We found that the density distribution with depth is compatible with previous models. Moreover, results support the hypothesis based on borehole evidence of a low-density upper basement across the entire area, possibly consisting of low-grade metamorphic rocks (phyllites). Finally, we compare our modeling results to the spatial distribution at depth of major seismic events between August and November 2016. These events appear to be concentrated within the denser units at both shallow and deep locations, while the deeper events often occur in a region of major density contrast corresponding to the top of the basement
The gravity anomaly of Mount Amiata; different approaches for understanding anomaly source distribution
No full textIn this work, the gravity anomaly signal beneath Mount Amiata and its surroundings have
been analysed to reconstruct the subsurface setting. In particular, the work focuses on the
investigation of the geological bodies responsible for the Bouguer gravity minimum observed
in this area.
Different approaches for understanding the Bouguer gravity anomaly source distribution,
including the calculation of the first vertical derivative of the gravity signal, the estimation of
the depth source using power spectrum analysis and the pseudo-3-D forward modeling, have
been considered. The gravity data employed were acquired from different institutions ENI,
OGS, USDMA and Servizio Geologico d’Italia and collected in a unique data set kindly made
available by ENI. It comes from about 50 000 stations, randomly distributed, which cover
Central Italy, with a spacing of less than 1 km.
We dedicated an active effort in:
(1) Defining the stratigraphic model (i.e. definition of the primary lithomechanical layers
within the sedimentary cover and the upper crust).
(2) Calculation of a new data set of density data derived from the velocity data collected by
active seismic surveys.
(3) Integration of stratigraphy, literature and new data in a comprehensive model.
The results of this study depict a body, with a density of 2.35 g cm−3, representing the
remnant magmatic chamber of Mount Amiata,which is responsible of the observed gravimetric
minimum. The top of the magmatic body is upward-convex, dislocated at a depth comprised
between 4.5 (beneath the volcano) and 7.5 km (in the peripheral zones) and draped by 2 km
thick, highly fractured hard rocks that could represent the fractured aureole of the magmatic
body itself. The 3-D modeling also defines the geometry of the Neogene Radicofani basin,
close to the eastern flank of the Mount Amiata and is imaged as a bowl-shaped basin with an
average depth of about 1500 m, and a maximum depth of about 2000 m reached towards north
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