324 research outputs found
Finite element modelling of stress field perturbations and interseismic crustal deformation in the Val d'Agri region, southern Apennines, Italy
The Val d'Agri area provides the opportunity to analyse active structures in a seismic region for which a large amount of subsurface data is available. This area, which was struck in 1857 by one of the most destructive earthquakes in Italy (MW = 7.03), represents a unique natural laboratory to gain new insights into geometry, modes and rates of faulting controlling crustal deformation in an actively extending orogen. In this study, a crustal geological section through the southern Apennines is discretized into a finite element model (FEM). We present a 2D elastoplastic FEM that reproduces stress perturbations and strain field around the Val d'Agri active fault system. The influence of fault strand activity on interseismic crustal deformation is tested by a series of computer models, whose predictions are compared with the horizontal velocity components of continuous GPS sites in the region and with stress directions and geological data. The best fit with available geological and geophysical constraints is obtained with a 300 km long, 29 km deep model formed by a multilayer including three components having different rheological characteristics and including several shallow, locked fault segments, which branch into a freely slipping major basement fault at depth. Finite element modelling provides new insights into the controversial and widely debated active tectonic setting of the study area, pointing out the fundamental role played by a structural reactivation process involving inherited, long-lived, mature fault systems at depth. Our FEM, reconciling apparently contrasting geological and geophysical constraints from the study area, points to maximum stress build up and strain accumulation at a depth of 15 ± 5 km. Such a depth range is suggested as the most likely one for the nucleation of large events such as the 1857 Val d'Agri earthquak
Active deformation and relief evolution in the western Lurestan region of the Zagros mountain belt: new insights from tectonic geomorphology analysis and finite element modeling
none7noopenBasilici, M.; Ascione, A.; Megna, A.; Santini, S.; Tavani, S.; Valente, E.; Mazzoli, S.Basilici, M.; Ascione, A.; Megna, A.; Santini, S.; Tavani, S.; Valente, E.; Mazzoli, S
Non-volcanic CO2 and CH4 degassing in an actively extending orogen, southern Apennines, Italy
The southern Apennines fold and thrust belt has been undergoing post-orogenic extension since ca. 700
kyr. Crustal extension controls active tectonics and seismogenesis in the mountain chain [1], with
seismicity being characterized by low to moderate magnitude events punctuated by strong earthquakes
[2]. Effective decoupling between deep and shallow structural levels is related to the strong rheological
contrast produced by a fluid-saturated, clay-rich mélange zone interposed between buried
autochthonous carbonates – continuous with those exposed in the Apulian foreland – and the
allochthonous units. This mélange zone also acts as a seal preventing the migration of deep-seated
aqueous fluids – as well as oil in the Basilicata region, which hosts the largest Europe’s onshore oil fields
– towards the surface.
On the other hand, the mountain belt is characterized by substantial gas flow, recorded as both
distributed soil gas emissions and vigorous gas vents, associated with active faults at the surface. We
measured a CO2 flux up to 34000 g/m-2 per day at a gas vent, as well as large amounts of He (up to 52
ppm), Rn (up to 228 kBq/m3) and CH4 (up to 5000 ppm).
Overpressured CO2, which has been proposed as triggering normal fault earthquakes in the Apennines,
has been interpreted as mostly of mantle origin. However, our new results from isotope analyses carried
out on the carbon contained in both CO2 and CH4 indicate a dominant thermogenic origin for these
gases, probably associated with the emplacement of magmatic sills within the lower section of the thick
carbonate platform succession occurring at the base of the sedimentary cover in the southern
Apennines. Our results bear major implication concerning the postulated occurrence of crustal faults
allowing fluids to migrate directly from mantle depths to the surface
Paleomagnetic and magnetic fabric data from Lower Triassic redbeds of the Central Western Carpathians: new constraints on the paleogeographic and tectonic evolution of the Carpathian region
In the Central Western Carpathians (CWC), most published paleomagnetic results from Permo-Mesozoic rocks
document extensive remagnetizations and come from thin-skinned thrust units that have undergone multistage deformation.We
present results from lower Triassic redbeds from the autochthonous cover overlying the basement that carry a primary
magnetization. Petromagnetic results indicate that the dominant ferromagnetic carrier is hematite, while magnetic susceptibility
and its anisotropy are controlled by both ferromagnetic and paramagnetic minerals. Magnetic fabrics document weak
deformation related to Late Cretaceous shortening. The directions of the high unblocking temperature remanence components
pass both reversal and fold tests, attesting to their primary nature. Paleomagnetic inclinations are flatter than expected from
reference datasets, suggesting small latitudinal separation between the CWC and stable Europe. Paleomagnetic declinations are
mostly clustered within individual mountain massifs, implying their tectonic coherence. They show only minor differences
between the massifs, indicating a lack of significant vertical-axis tectonic rotations within the studied central parts of the CWC.
The paleomagnetic declinations are therefore representative of the whole of the CWC in terms of regional paleogeographic
interpretations, and imply moderate counterclockwise rotations (c. 26°) of the region with respect to stable Europe since the
Early Triassic
Controls of Radiogenic Heat and Moho Geometry on the Thermal Setting of the Marche Region (Central Italy): An Analytical 3D Geothermal Model
none7sìopenSantini, S.; Basilici, M.; Invernizzi, C.; Jablonska, D.; Mazzoli, S.; Megna, A.; Pierantoni, P.P.Santini, S.; Basilici, M.; Invernizzi, C.; Jablonska, D.; Mazzoli, S.; Megna, A.; Pierantoni, P. P
thermal structure of the outer northern apennines along the crop 03 profile
In this study, we elaborated a 2D model that reproduces the thermal structure of the central-northern Adriatic offshore and adjacent onshore area of the Italian peninsula. Based on the crustal structure along the trace of the CROP-03 deep section, the geotherms offshore Gabicce (northern Marche region) were obtained by an analytical procedure taking into account the role of thrusting within the sedimentary cover. Basement involvement at depth beneath the neighbouring Mondaino area to the SW, where a crustal thrust ramp dips towards the hinterland, required the use of a different analytical procedure. The results obtained in this study allowed us to define a satisfactory description of the thermal state of the northern Marche coastal area and adjacent Adriatic offshore. These results, integrated with those obtained by previous studies, confirm that the isotherms of 250°C and 400°C are placed in the stable Adriatic lithosphere at depths of about 11 km and 22 km, respectively. Furthermore, the 400°C isotherm is deeper in the onshore area, reaching a depth of about 30 km in the zone comprised between Gabicce and Mondaino, whereas the 250°C isotherm deepens towards the SW along the Adriatic Sea sector, to reach a maximum depth of 13 km in coastal area, rising again at a depth of 11 km in the innermost sector of the studied section
Quaternary deformation in SE Sicily: Insights into the life and cycles of forebulge fault systems
Integrated geological, geomorphological, and differential interferometry synthetic aperture radar (DInSAR) data are used to constrain the
timing and modes of activity of Quaternary fault systems in the Hyblean Plateau. This area, which represents a unique natural laboratory
for studying surface deformation in relation to deep slab dynamics, has grown since middle Miocene times as a doubly plunging forebulge
associated with slab rollback during NW-directed subduction. Bimodal extension has produced two mutually orthogonal normal fault systems.
The detailed stratigraphic record provided by synrift sediments and postrift marine terraces allowed us to define the timing of activity
of an early Pleistocene, flexure-related fault system, thus constraining the duration of a typical foreland extensional tectonic event to
~1.5 m.y. Subsequent late Quaternary to present deformation was dominated by strike-slip faulting associated with NW-oriented horizontal
compression. During this latest stage, regional uplift progressively increased toward the thrust front to the NW and was accompanied by
differential uplift accommodated by dip-slip components of motion along active NNW-trending faults. The general active tectonic setting of
the study area, characterized by NW-oriented horizontal compression consistent with major plate convergence, and the regional uplift pattern
can both be explained within the framework of intraplate shortening and foreland rebound following complete slab detachment, a major
geodynamic event interpreted to have taken place at ca. 0.7 Ma in southern Italy
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