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Coco, Armando
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- PublicationOpen AccessNumerical models for ground deformation and gravity changes during volcanic unrest: simulating the hydrothermal system dynamics of a restless caldera(2016)
; ; ; ; ; ; ; ;Coco, A.; Bristol University ;Gottsmann, J; Bristol University ;Whitaker, F; Bristol University ;Rust, A; Bristol University ;Currenti, G; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia ;Jasim, A; Bristol University ;Bunney, S; Bristol University; ; ; ; ; ; Ground deformation and gravity changes in restless calderas during periods of unrest can signal an impending eruption and thus must be correctly interpreted for hazard evaluation. It is critical to differentiate variation of geophysical observables related to volume and pressure changes induced by magma migration from shallow hydrothermal activity associated with hot fluids of magmatic origin rising from depth. In this paper we present a numerical model to evaluate the thermo-poroelastic response of the hydrothermal system in a caldera setting by simulating pore pressure and thermal expansion associated with deep injection of hot fluids (water and carbon dioxide). Hydrothermal fluid circulation is simulated using TOUGH2, a multicomponent multiphase simulator of fluid flows in porous media. Changes in pore pressure and temperature are then evaluated and fed into a thermo-poroelastic model (one-way coupling), which is based on a finite-difference numerical method designed for axi-symmetric problems in unbounded domains. Informed by constraints available for the Campi Flegrei caldera (Italy), a series of simulations assess the influence of fluid injection rates and mechanical properties on the hydrothermal system, uplift and gravity. Heterogeneities in hydrological and mechanical properties associated with the presence of ring faults are a key determinant of the fluid flow pattern and consequently the geophysical observables. Peaks (in absolute value) of uplift and gravity change profiles computed at the ground surface are located close to injection points (namely at the centre of the model and fault areas). Temporal evolution of the ground deformation indicates that the contribution of thermal effects to the total uplift is almost negligible with respect to the pore pressure contribution during the first years of the unrest, but increases in time and becomes dominant after a long period of the simulation. After a transient increase over the first years of unrest, gravity changes become negative and decrease monotonically towards a steady-state value. Since the physics of the investigated hydrothermal system is similar to any fluid-filled reservoir, such as oil fields or CO2 reservoirs produced by sequestration, the generic formulation of the model will allow it to be employed in monitoring and interpretation of deformation and gravity data associated with other geophysical hazards that pose a risk to human activity.277 148 - PublicationOpen AccessSpectral and norm estimates for matrix-sequences arising from a finite difference approximation of elliptic operators(2023-03-09)
; ; ; ; ; ; ; ; ; When approximating elliptic problems by using specialized approximation techniques, we obtain large structured matrices whose analysis provides information on the stability of the method. Here we provide spectral and norm estimates for matrix-sequences arising from the approximation of the Laplacian via ad hoc finite differences. The analysis involves several tools from matrix theory and in particular from the setting of Toeplitz operators and Generalized Locally Toeplitz matrix-sequences. Several numerical experiments are conducted, which confirm the correctness of the theoretical findings.29 8 - PublicationOpen AccessEffects of hydrothermal unrest on stress and deformation: insights from numerical modeling and application to Vulcano Island (Italy)(2017)
; ; ; ; ; ; ;A numerical approach is proposed to evaluate stress and deformation fields induced by hydrothermal fluid circulation and its influence on volcano-flank stability. The numerical computations have been focused on a conceptual model of Vulcano Island, where geophysical, geochemical, and seismic signals have experienced several episodes of remarkable changes likely linked to the hydrothermal activity. We design a range of numerical models of hydrothermal unrest and computed the associated deformation and stress field arising from rock-fluid interaction processes related to the thermoporoelastic response of the medium. The effects of model parameters on deformation and flank stability are explored considering different multilayered crustal structures constrained by seismic tomography and stratigraphy investigations. Our findings highlight the significant role of model parameters on the response of the hydrothermal system and, consequently, on the amplitudes and the timescale of stress and strain fields. Even if no claim is made that the model strictly applies to the crisis episodes at Vulcano, the numerical results are in general agreement with the pattern of monitoring observations, characterized by an enhancing of gas emission and seismic activity without significant ground deformation.The conceptual model points to a pressurization and heating of the shallow hydrothermal system (1–0.25 km bsl) fed by fluid of magmatic origin. However, for the assumed values of model material and source parameters (rate of injection, fluid composition, and temperature), the pressure and temperature changes do not affect significantly the flank stability, which is mainly controlled by the gravitational force.494 39 - PublicationOpen AccessA hydro-geophysical simulator for fluid and mechanical processes in volcanic areas.(2016)
; ; ; ; ; ;Coco, A.; Bristol University ;Currenti, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia ;Gottsmann, J.; Bristol University ;Russo, G.Del Negro, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, ItaliaEfficient and accurate hydrothermal and mechanical mathematical models in porous media constitute a fundamental tool for improving the understanding of the subsurface dynamics in volcanic areas. We propose a finite-difference ghost-point method for the numerical solution of thermo-poroelastic and gravity change equations. The main aim of this work is to study how the thermo-poroelastic solutions vary in a realistic description of a specific volcanic region, focusing on the topography and the heterogeneous structure of Campi Flegrei (CF) caldera (Italy). Our numerical approach provides the opportunity to explore different model configurations that cannot be taken into account using standard analytical models. Since the physics of the investigated hydrothermal system is similar to any saturated reservoir, such as oil fields or CO2 reservoirs produced by sequestration, the model is generally applicable to the monitoring and interpretation of both deformation and gravity changes induced by other geophysical hazards that pose a risk to human activity.237 158 - PublicationRestrictedA second order finite-difference ghost-point method for elasticity problems on unbounded domains with applications to volcanology(2014)
; ; ; ; ;Coco, A.; Bristol University ;Currenti, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia ;Del Negro, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia ;Russo, G.; Università di Catania; ; ; We propose a novel nite-di erence approach for the numerical solution of linear elasticity problems in arbitrary unbounded domains. The method is an extension of a recently proposed ghost-point method for the Poisson equation on bounded domains with arbitrary boundary conditions (Coco, Russo, JCP, 2013) to the case of the Cauchy-Navier equations on unbounded domains. The technique is based on a smooth coordinate transformation, which maps an unbounded domain into a unit square. Arbitrary geometries are de ned by suitable level-set functions. The equations are discretized by classical ninepoint stencil on interior points, while boundary conditions and high order reconstructions are used to de ne the eld variable at ghost-point, which are grid nodes external to the domain with a neighbor inside the domain. The approach is then adopted to solve elasticity problems applied to volcanology for computing the displacement caused by an underground pressure source. The method is suitable to treat problems in which the geometry of the source often changes (explore the e ects of di erent scenarios, or solve inverse problems in which the geometry itself is part of the unknown), since it does not require complex re-meshing when the geometry is modi ed. Several numerical tests are performed, which asses the e ectiveness of the present approach. Keywords: Linear Elasticity, Cauchy-Navier equations, ground deformation, unbounded domain, coordinate transformation method, Cartesian grid, Ghost points, Level-set methods245 46