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  • 1
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    Accuracy of fully coupled and sequential approaches for modeling hydro- and geomechanical processes (2020)
    Springer International Publishing
    Details
    Publication Date: 2023-06-09
    Description: Subsurface flow and geomechanics are often modeled with sequential approaches. This can be computationally beneficial compared with fully coupled schemes, while it requires usually compromises in numerical accuracy, at least when the sequential scheme is non-iterative. We discuss the influence of the choice of scheme on the numerical accuracy and the expected computational effort based on a comparison of a fully coupled scheme, a scheme employing a one-way coupling, and an iterative scheme using a fixed-stress split for two subsurface injection scenarios. All these schemes were implemented in the numerical simulator DuMux. This study identifies conditions of problem settings where differences due to the choice of the model approach are as important as differences in geologic features. It is shown that in particular transient and multiphase flow, effects can be causing significant deviations between non-iterative and iterative sequential schemes, which might be in the same order of magnitude as geologic uncertainty. An iterated fixed-stress split has the same numerical accuracy as a fully coupled scheme but only for a certain number of iterations which might use up the computational advantage of solving two smaller systems of equations rather than a big monolithical one.
    Description: Deutsche Forschungsgemeinschaft https://doi.org/10.13039/501100001659
    Description: H2020 European Research Council https://doi.org/10.13039/100010663
    Keywords: ddc:550.2 ; Flow and geomechanics ; Fully coupled and sequential schemes ; Fixed-stress scheme ; Numerical accuracy ; Geologic uncertainty
    Language: English
    Type: doc-type:article
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  • 2
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    Buoyancy Effects on Upward Brine Displacement Caused by CO2 Injection (2012)
    Springer Science+Business Media B.V.
    Details
    Publication Date: 2020-02-24
    Description: Upward displacement of brine from deep reservoirs driven by pressure increases resulting fromCO2 injection for geologic carbon sequestrationmay occur through improperly sealed abandoned wells, through permeable faults, or through permeable channels between pinch-outs of shale formations. The concern about upward brine flow is that, upon intrusion into aquifers containing groundwater resources, the brinemay degrade groundwater. Because both salinity and temperature increase with depth in sedimentary basins, upward displacement of brine involves lifting fluid that is saline but also warm into shallower regions that contain fresher, cooler water. We have carried out dynamic simulations using TOUGH2/EOS7 of upward displacement of warm, salty water into cooler, fresher aquifers in a highly idealized two-dimensional model consisting of a vertical conduit (representing a well or permeable fault) connecting a deep and a shallow reservoir. Our simulations show that for small pressure increases and/or high-salinity-gradient cases, brine is pushed up the conduit to a new static steady-state equilibrium. On the other hand, if the pressure rise is large enough that brine is pushed up the conduit and into the overlying upper aquifer, flow may be sustained if the dense brine is allowed to spread laterally. In this scenario, dense brine only contacts the lower-most region of the upper aquifer. In a hypothetical case in which strong cooling of the dense brine occurs in the upper reservoir, the brine becomes sufficiently dense that it flows back down into the deeper reservoir from where it came. The brine then heats again in the lower aquifer and moves back up the conduit to repeat the cycle. Parameter studies delineate steady-state (static) and oscillatory solutions and reveal the character and period of oscillatory solutions. Such oscillatory solutions aremostly a curiosity rather than an expected natural phenomenon because in nature the geothermal gradient prevents the cooling in the upper aquifer that occurs in the model. The expected effect of upward brine displacement is either establishment of a new hydrostatic equilibrium or sustained upward flux into the bottom-most region of the upper aquifer.
    Description: Published
    Description: 525-540
    Description: JCR Journal
    Description: restricted
    Keywords: Geologic carbon sequestration ; 04. Solid Earth::04.04. Geology::04.04.99. General or miscellaneous
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 3
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    The Effect of a Mainshock on the Size Distribution of the Aftershocks (2019)
    Details
    Publication Date: 2019-10-10
    Description: A systematic decay of the aftershock rate over time is one of the most fundamental empirical laws in Earth science. However, the equally fundamental effect of a mainshock on the size distribution of subsequent earthquakes has still not been quantified today and is therefore not used in earthquake hazard assessment. We apply a stacking approach to well-recorded earthquake sequences to extract this effect. Immediately after a mainshock, the mean size distribution of events, or b-value, increases by 20-30%, considerably decreasing the chance of subsequent larger events. This increase is strongest in the immediate vicinity of the mainshock, decreasing rapidly with distance but only gradually over time. We present a model that explains these observations as a consequence of the stress changes in the surrounding area caused by the mainshocks slip. Our results have substantial implications for how seismic risk during earthquake sequences is assessed.
    Description: Published
    Description: 13277–13287
    Description: 6T. Studi di pericolosità sismica e da maremoto
    Description: JCR Journal
    Keywords: 04. Solid Earth
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 4
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    Effects of atmospheric conditions on surface diffuse degassing (2012)
    Details
    Publication Date: 2019-10-10
    Description: Diffuse degassing through the soil is commonly observed in volcanic areas and monitoring of carbon dioxide flux at the surface can provide a safe and effective way to infer the state of activity of the volcanic system. Continuous measurement stations are often installed on active volcanoes such as Furnas (Azores archipelago), which features low temperature fumaroles, hot and cold CO2 rich springs, and several diffuse degassing areas. As in other volcanoes, fluxes measured at Furnas are often correlated with environmental variables, such as air temperature or barometric pressure, with daily and seasonal cycles that become more evident when gas emission is low. In this work, we study how changes in air temperature and barometric pressure may affect the gas emission through the soil. The TOUGH2 geothermal simulator was used to simulate the gas propagation through the soil as a function of fluctuating atmospheric conditions. Then, a dual parameters study was performed to assess how the rock permeability and the gas source properties affect the resulting fluxes. Numerical results are in good agreement with the observed data at Furnas, and show that atmospheric variables may cause the observed daily cycles in CO2 fluxes. The observed changes depend on soil permeability and on the pressure driving the upward flux.
    Description: Published
    Description: B11201
    Description: 3.6. Fisica del vulcanismo
    Description: 4.3. TTC - Scenari di pericolosità vulcanica
    Description: JCR Journal
    Description: restricted
    Keywords: diffuse degassing ; atmospheric pressure ; numerical modeling ; porous media ; volcano monitoring ; carbon dioxide ; 04. Solid Earth::04.08. Volcanology::04.08.01. Gases ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 5
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    Modeling of unrest signals in heterogeneous hydrothermal systems (2010)
    American Geophysical Union
    Details
    Publication Date: 2019-10-10
    Description: An edited version of this paper was published by AGU. Copyright (2010) American Geophysical Union.
    Description: Monitoring of quiescent volcanoes, such as Campi Flegrei (Italy), involves the measurement of geochemical and geophysical parameters that are expected to change as eruptive conditions approach. Some of these changes are associated with the hydrothermal activity that is driven by the release of heat and magmatic fluids. This work focuses on the properties of the porous medium and on their effects on the signals generated by the circulating fluids. The TOUGH2 porous media flow model is applied to simulate a shallow hydrothermal system fed by a source of magmatic fluids. The simulated activity of the source, with periods of increased fluid discharge, generates changes in gas composition, gravity, and ground deformation. The same boundary conditions and source activity were applied to simulate the evolution of homogeneous and heterogeneous systems, characterized by different rock properties. Phase distribution, fluid composition, and the related signals depend on the nature and properties of the rock sequence through which the fluids propagate. Results show that the distribution of porosity and permeability affects all the observable parameters, controlling the timing and the amplitude of their changes through space and time. Preferential pathways for fluid ascent favor a faster evolution, with larger changes near permeable channels. Slower changes over wider areas characterize less permeable systems. These results imply that monitoring signals do not simply reflect the evolution of the magmatic system: intervening rocks leave a marked signature that should be taken into account when monitoring data are used to infer system conditions at depth.
    Description: This work was carried out within the research project V1-UNREST, founded by the Italian Civil Protection Department
    Description: Published
    Description: B09213
    Description: 3.6. Fisica del vulcanismo
    Description: JCR Journal
    Description: open
    Keywords: hydrothermal circulation ; observable ; volcanic unrest ; permeability ; 03. Hydrosphere::03.04. Chemical and biological::03.04.06. Hydrothermal systems ; 04. Solid Earth::04.08. Volcanology::04.08.01. Gases ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 6
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    Hydrothermal instability and ground displacement at the Campi Flegrei caldera (2010)
    Elsevier
    Details
    Publication Date: 2019-10-10
    Description: Ground deformation is commonly observed at active volcanoes, where it represents a reliable sign of unrest and a potential precursor of eruptive activity. The source of deformation, however, is not always unequivocally constrained. Magma ascent and differentiation are generally involved, but hydrothermal fluids may play a role, due to thermal expansion and pore pressure acting on rocks. The identification of mechanisms driving ground displacement bears important consequences for hazard evaluation. The aim of this work is to evaluate mechanical effects associated with pressurization and heating of hydrothermal fluids. We first simulate the heat and fluid flow driven by the arrival of magmatic fluids from greater depth. Then, we calcu- late the rock deformation arising from simulated pressure and temperature changes within a shallow hydrothermal system. We employ a mathematical model, based on the linear theory of thermo-poro-elasticity and on a system of distributed equivalent forces. Results show that stronger degassing of a magmatic source may cause several centimeters of uplift.
    Description: INGV-DPC Project V1 Unrest
    Description: Published
    Description: 155-161
    Description: 3.6. Fisica del vulcanismo
    Description: 4.3. TTC - Scenari di pericolosità vulcanica
    Description: JCR Journal
    Description: open
    Keywords: Hydrothermal system ; ground deformation ; poro-elasticity ; volcanic unrest ; 04. Solid Earth::04.08. Volcanology::04.08.99. General or miscellaneous
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 7
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    MONITORING AND MODELLING HYDROTHERMAL PANAREA SYSTEM (AEOLIAN ISLAND): GPS AND VOLCANOLOGICAL DATA (2008)
    Details
    Publication Date: 2019-10-10
    Description: In November 2002 a submarine gas eruption started offshore 3 Km east of Panarea island (Aeolian Island) on top of a shallow rise of 2.3 km2 surrounded by islets forming a small archipelago. This event has posed new concern on a volcano generally considered extinct. Panarea island and its archipelago (~ 3.3 km2) are the emergent portion of submarine stratovolcano more than 2000 m high and 20 Km across; exhalative activity due to a shallow hydrothermal system is well known since historical times. To monitor and study ground deformation associated with anomalous gas emission, a local GPS network (PANAREA) was designed, set up and measured during time span December 2002 - October 2006. The network consists of nine sites (six constructed after 2002) located on Panarea and on the islets. GPS data analysis was performed combining episodic campaigns of Panarea and other local networks located in the Aeolian area, carried out between 1995 and 2006, and data of continuous European and Italian sites. The results show at Panarea volcano two distinct crustal domains characterized by different kinematics and styles of deformation. The merging of GPS and structural data suggest the relationship among gas vent distribution, submarine volcanological structures and ground deformations. The actual distribution of the estimated strain-rate is consistent with the structural setting.The general subsidence and shortening in the islets area can be interpreted as the response of the surface to the variation of the hydrothermal system reservoir which is progressively reducing its pressure after the gas eruption. A simple first order approach to the modelling of the hydrothermal system is the use of Okada sources.To evaluate the coupled thermo-hydro-mechanical processes going on in Panarea, a two-step model will be implemented. The model first involves the simulation of pore pressure and temperature changes due to fluid circulation. Then the mechanical response of the porous rock is calculated based on the linear theory of poro-elasticity.
    Description: Unpublished
    Description: Reykjavík, Iceland
    Description: 1.3. TTC - Sorveglianza geodetica delle aree vulcaniche attive
    Description: open
    Keywords: GPS, monitoring, Aeolian Islands ; 04. Solid Earth::04.03. Geodesy::04.03.01. Crustal deformations ; 04. Solid Earth::04.07. Tectonophysics::04.07.02. Geodynamics
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: Oral presentation
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  • 8
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    MODELING OF HYDROTHERMAL FLUID CIRCULATION AS A TOOL FOR VOLCANIC HAZARD ASSESSMENT (2010)
    Details
    Publication Date: 2020-02-25
    Description: Monitoring of geophysical and geochemical observ¬ables at the surface plays a main role in the under¬standing of—and the hazard evaluation of— active volcanoes. Measurable changes in these parameters should occur when a volcano approches eruptive con¬ditions. Hydrothermal activity is commonly studied as an efficient carrier of signals from the magmatic system. As the magmatic system evolves, the amount, temperature, and composition of magmatic fluids that feed the hydrothermal system change, in turn affecting the parameters that are monitored at the surface. Modeling of hydrothermal circulation, as shown in the past, may cause measurable gravity changes and ground deformation. In this work, we extend our previous studies and increase the number of observable parameters to include gas temperature, the rate of diffuse degassing, the extent of the degassing area, and electrical conductivity. The possibility of nonmagmatic disturbance needs to be carefully addressed to ensure a proper estimate of volcanic hazard.
    Description: DPC INGV Project V1 - Unrest
    Description: Published
    Description: Lawrence Berkeley National Laboratory, Berkeley, CA
    Description: 3.6. Fisica del vulcanismo
    Description: 4.3. TTC - Scenari di pericolosità vulcanica
    Description: open
    Keywords: hydrothermal system ; volcanic unrest ; electrical resistivity ; modeling ; 04. Solid Earth::04.08. Volcanology::04.08.99. General or miscellaneous
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: Extended abstract
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  • 9
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    Electrical conductivity, ground displacement, gravity changes, and gas flow at Solfatara crater (Campi Flegrei caldera, Italy): Results from numerical modeling (2012)
    Elsevier Science Limited
    Details
    Publication Date: 2020-02-24
    Description: Hydrothermal fluid circulation may cause measurable gravity changes and ground deformation. We extend our previous studies and increase the number of observable parameters to include gas temperature, the rate of diffuse degassing, the extent of the degassing area, and electrical conductivity. We have carried out simulations using TOUGH2/EOS2 of a large scale hydrothermal system, then we have calculated observables arising from changes in hydrothermal fluid circulation. Our results show that fluids affect many observable parameters generating detectable signals. However, a more detailed description of the shallow subsurface is necessary to properly calculate electrical conductivity. Studies at Solfatara volcano (Campi Flegrei caldera, Italy) highlight the presence of an unsaturated layer at depth and allow to determine the position of the water table. Then, we present results from a new, small scale simulation, focused on the crater, and carried out with a new, refined meshgrid taking into account the real topography. Aim of the work is to calculate a detailed electrical conductivity map and reproduce the main features of the Solfatara crater.
    Description: Published
    Description: 93–105
    Description: JCR Journal
    Description: restricted
    Keywords: Electrical conductivity ; 04. Solid Earth::04.08. Volcanology::04.08.99. General or miscellaneous
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 10
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    The November 2017 Mw 5.5 Pohang earthquake: A possible case of induced seismicity in South Korea (2018)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2018-06-01
    Description: The moment magnitude ( M w ) 5.5 earthquake that struck South Korea in November 2017 was one of the largest and most damaging events in that country over the past century. Its proximity to an enhanced geothermal system site, where high-pressure hydraulic injection had been performed during the previous 2 years, raises the possibility that this earthquake was anthropogenic. We have combined seismological and geodetic analyses to characterize the mainshock and its largest aftershocks, constrain the geometry of this seismic sequence, and shed light on its causal factors. According to our analysis, it seems plausible that the occurrence of this earthquake was influenced by the aforementioned industrial activities. Finally, we found that the earthquake transferred static stress to larger nearby faults, potentially increasing the seismic hazard in the area.
    Keywords: Geochemistry, Geophysics
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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