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Santini, Stefano
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Santini, Stefano
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Santini, S.
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santini@fis.uniurb.it
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25 results
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- PublicationOpen AccessGeothermal Model of the Shallow Crustal Structure across the “Mountain Front Fault” in Western Lurestan, Zagros Thrust Belt, Iran(2019)
; ; ; ; ; ; ; ; ; The Zagros thrust belt is a zone of deformed crustal rocks well exposed along the southwest region of Iran. To obtain a better knowledge of this mountain chain, we elaborated a 2D model reproducing the thermal structure of the “Mountain Front Fault”. This study, which is focused on the Lurestan region, is based on a model made by merging published sections and available information on the depth of the Moho. We present the isotherms and the geotherms calculated using an analytical methodology. The calculation procedure includes the temperature variation due to the re-equilibrated conductive state after thrusting, frictional heating, heat flow density data, and a series of geologically derived constraints. In order to perform the temperature calculations, the crustal structure in the Lurestan region is simplified as composed of two domains: A lower unit made by crystalline basement and an upper unit including all the lithostratigraphic units forming the sedimentary cover. The resulting model is compared with the numerical results obtained by previous studies to improve the description of the thermal structure of this geologically important area.62 21 - PublicationOpen AccessNormal-fault stress and displacement through finite-element analysis(2005-12)
; ; ; ;Megna, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Barba, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Santini, S.; Istituto di Fisica, Università degli Studi di Urbino, Italy; ; We compute displacement and stress due to a normal fault by means of two-dimensional plane-strain finite-element analysis. To do so, we apply a system of forces to the fault nodes and develop an iterative algorithm serving to determine the force magnitudes for any slip distribution. As a sample case, we compute the force magnitudes assuming uniform slip on a 10-km two-dimensional normal fault. The numerical model generates displacement and stress fields that compare well with the analytical solution. In fact, we found little difference in displacements (<5%), displacement orientation (<15°), and stress components (<35%, half of which due to slip tolerance). We analyze such misfit, and discuss how the error propagates from displacement to stress. Our scheme provides a convenient way to use the finite-elements direct method in a trial-and-error procedure to reproduce any smooth slip distribution.215 250 - PublicationOpen AccessA perturbative solution of the power-law viscoelastic constitutive equation for lithospheric rocks(1996-12)
; ; ; ; ;Dragoni, M.; Dipartimento di Geologia e Geofisica, Università di Bari, Italy ;Lenci, T.; Bayerischen Geoinstitut, Universitat Bayreuth, Germany ;Santini, S.; Istituto di Fisica, Università di Urbino, Italy ;Vetrano, F.; Istituto di Fisica, Università di Urbino, Italy ;; ;A power-law, viscoelastic constitutive equation for lithospheric rocks, is considered. The equation is a nonlinear generalization of the Maxwell constitutive equation, in which the viscous deformation depends on the n-th power of deviatoric stress, and describes a medium which is elastic with respect to normal stress, but relaxes deviatoric stress. Power-law exponents equal to 2 and 3, which are most often found in laboratory experiments, are considered. The equation is solved by a perturbative method for a viscoelastic layer subjected to a constant, extensional or compressional, strain rate and yields stress as a function of time, temperature and rock composition. The solution is applied to an ideal extensional boundary zone and shows that the base of the crustal seismogenic layer may be deeper than predicted by a linear rheology.150 135 - PublicationRestrictedStructural inheritance controlling active crustal deformation in the Val d’Agri area (southern Apennines, Italy): new insights from finite element modelling(2017-03)
; ; ; ; ; The availability of a large amount of surface geological data and subsurface information gathered by the oil industry, together with seismic and geodetic data, allowed us to define and analyse the active structures in the Val d'Agri area of the southern Apennines. Taking into account that the study of interseismic deformation can be significant to identify locked fault areas that can potentially slip, in this study we present 2D elastoplastic finite-element models to reproduce interseismic characteristics of the study area. This hosts the largest Europe's onshore oil field and is characterised by an active extensional tectonic regime, as inferred from earthquake focal mechanisms and fault slip data from late Quaternary structures. Based on high-quality seismic profiles tied with deep well logs, we constructed a detailed geological section across the study area. Outcropping units are dissected by numerous brittle structures that formed at various stages during the tectonic evolution of the Apennines, while the deep ones are dominated by deeply rooted major faults. The rheological behaviour has been constrained by the reconstruction of the thermal structure of the fold and thrust belt, using available information from the foreland Apulian Platform and from temperature data from a series of wells. Starting from the geological model, we reproduced interseismic deformation by means of finite-element numerical modelling, varying boundary conditions and unlocking different fault segments. Our numerical models provide new insights into the controversial and widely debated active tectonic setting of the Val d'Agri area, confirming the major role played by structural inheritance and reactivation processes. In fact, recent low-magnitude seismicity tends to illuminate fault segments consisting of pre-existing reverse faults reactivated as normal faults in the present-day stress field. These long-lived, mature fault systems occurring in the buried Apulian Platform carbonates (and underlying basement) represent major brittle structures that cumulated displacements of up to a few kilometres over geologic time. As a result of their reactivation within the late Quaternary extensional stress field, these long-lived crustal structures are capable of nucleating also moderate- to large-magnitude earthquakes. The decoupling between deep and shallow structural levels, and the different inherited structures affecting them, explain the apparent contrast between the subdued surface expression of active fault systems and the known occurrence of large magnitude seismic events in the study area, thus reconciling apparently contrasting geological and geophysical constraints.173 28 - PublicationOpen AccessUno studio sulla sismicità del Montefeltro (Appennino settentrionale, Italia centrale) nel periodo 2005-2017(2018-11)
; ; ; ; ; ; ; Il territorio del Montefeltro comprende la parte occidentale dell’attuale provincia di Rimini, in Emilia-Romagna, e la parte settentrionale della provincia di Pesaro-Urbino, nelle Marche. L’area è interessata da una sismicità piuttosto diffusa e, salvo alcune fasi di attività più intensa, sporadica nel tempo con magnitudo sostanzialmente medio-basse. La pericolosità sismica della regione è classificata medio-alta (zona 2), corrispondentemente a valori dell’accelerazione massima compresi tra 0.150 e 0.225g (Mappa di pericolosità sismica, 2006 – http://zonesismiche.mi.ingv.it). In questo studio si esamina la sismicità del Montefeltro partendo dalla rilocalizzazione di un data set aggiornato di eventi registrati dalla RSN nel periodo 2005-2017 (database ISIDe - http://iside.rm.ingv.it/iside/standard/).81 72 - PublicationOpen AccessSpace-time variations of the Umbria-Marche region instrumental seismicity(2000-10)
; ; ; ; ;Megna, A.; Istituto Nazionale di Geofisica, Roma, Italy ;Barba, S.; Istituto Nazionale di Geofisica, Roma, Italy ;Santini, S.; Istituto di Fisica, Università di Urbino, Urbino, Italy ;Vetrano, F.; Istituto di Fisica, Università di Urbino, Urbino, Italy; ; ;In the Umbria-Marche region, space and time variations concerning the b value were studied by instrumental seismicity from January 1987 to May 1999, according to the Bender method. Data were divided into two partially independent data sets. The first set, (January 1987 - December 1996), does not include the Colfiorito seismic sequence that occurred in the autumn of 1997. The second data set includes all events from January 1987 to May 1999. Using square cell dimensions of 80, 40 and 20 km, the examined area was divided respectively into three grids. The b value was estimated for each cell using the first data set, thus allowing us to reveal b value space variations and determine the resolution. To evaluate the stability of our result we estimated the b value on the basis of historical seismicity within the region. Several synthetic tests were also performed to estimate the stability of the Bender method and to verify its consistency with respect to other methods commonly used. Finally we estimated the b values using the second data set to prove the time variations. Results from the area examined show that the lowest possible spatial resolution of the b value is about 40 km and that there is a correlation between the b value pattern and the main active tectonic structures of the area. The most important time variations occur within the Colfiorito area, in which the b value drops significantly within the second data set. Results suggest two different ways of strain release: the first one produces continuous seismicity that spreads all over the examined area, while the second, which concerns stronger earthquakes, is localized.165 322 - PublicationOpen AccessGeothermal 3D model of the shallow crustal structure in the Val d’Agri oil field (Basilicata region)(2017-07-10)
; ; ; ; ; ; ; A good understanding of the geothermal gradient in any region is of primary importance for hydrocarbon/geothermal reservoir management and further applications in the fields of (e.g.) subsurface CO2 storage and nuclear waste disposal. In the particular case of the Basilicata oil fields area, the analytical definition of the geotherms carried out in this study is particularly relevant, both for industrial applications and for seismotectonic modelling in a region characterized by a magnitude 7 historical earthquake. In fact, the thermal state plays a fundamental role in controlling the modes of strain accommodation in the crust, which in turn controls the partitioning and distribution of seismic vs. aseismic strain. A geothermal model for the area of the Val d’Agri oil fields has been obtained by an analytical procedure. The model takes into account both the temperature variation due to the re-equilibrated conductive state after thrusting and frictional heating. Input parameters include heat flow density data and a series of geologically derived constraints – thrust depth, timing of thrusting, slip rate – obtained by the integration of surface and subsurface datasets. This work, representing a first attempt to reconstruct a geothermal 3D model for the Val d’Agri seismic zone of the Basilicata region, provides thermal constraints that could constitute a basis for future studies in the area.130 136 - PublicationOpen AccessGeothermal 3D model of the shallow crustal structure of the Alta Val d’Agri area (southern Apennines)A geothermal model for the area of the Val d’Agri oil fields has been obtained by an analytical procedure. The model takes into account both the temperature variation due to the re-equilibrated conductive state after thrusting and frictional heating. Input parameters include heat flow density data and a series of geologically derived constraints - thrust depth, timing of thrusting, slip rate - obtained by the integration of surface and subsurface datasets. The results of this work, representing a first attempt to reconstruct a geothermal 3D model for the Val d’Agri zone of the Basilicata region, emphasize two main regional features: (i) the isotherms relative to temperatures lower than 350 °C are roughly parallel and sub-horizontal across the whole study area, tending to deepen just along the NE-most edge of the investigated region; (ii) the isotherms relative to temperatures greater than 350 °C tend to deepen toward the center of the valley. Therefore, while the thermal structure at mid crustal depths appears to be perturbed and roughly mirroring the surface valley, the seismogenic upper crust of the study area is characterized by an unperturbed, roughly homogeneous and regular thermal structure.
131 168 - PublicationOpen AccessA Waveform Dataset in Continuous Mode of the Montefeltro Seismic Network (MF) in Central-Northern Italy from 2018 to 2020(2022)
; ; ; ; ; ; ; ; ; The Montefeltro seismic network (FDSN Network code: 1S) was deployed in the Apennines area of northern Marche and southern Emilia-Romagna regions (central Italy). A temporary network was set up in December 2018 and continues to operate, with an array consisting of stations equipped with dynamic digitizers and three-component short/extended/broad band seismometers (Guralp CMG/20s and 30s, Lennartz 3D/5s, Sara SS20 3D/0.5s sensors). The network records in continuous mode at 100 sps. The data are used to analyze the seismic activity and the spatiotemporal evolution of small seismic sequences occurring in the considered area and surrounding zones, strongly clustered in time and space. The data of dataset files are mini-seed formatted and subdivided by the following tree: (1) the dataset is divided by years; (2) the dataset is then subdivided by stations; (3) finally, the data are divided by days of each year in every station folder.52 11 - PublicationOpen AccessEffects of geological complexities on coseismic displacement(2008-06)
; ; ; ; ;Megna, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Barba, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Santini, S.; Istituto di Fisica, Università degli Studi di Urbino ;Dragoni, M.; Settore di Geofisica, Dip. di Fisica, Università degli Studi di Bologna; ; ;By means of a 2D finite-element procedure, we tested how heterogeneities at the scale of seismogenic fault affect the displacement. We defined one or more slip distributions for two typical normal-faulting earthquakes in the Central Apennines, computed the displacement occurred within different structures including lateral heterogeneities, and compared the different displacement profiles to isolate the effect of the crustal structure. To understand at what magnitude the heterogeneities affect the observation significantly, we compared the predicted coseismic displacement with GPS and DInSAR data for the Colfiorito 1997 earthquake. We find that heterogeneities significantly affect the observable horizontal coseismic displacement for the larger magnitudes, whereas for smaller quakes, they affect horizontal displacement close to the fault trace only.230 241
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