Demonstration Project: Evaluation of The Mofete High Enthalpy Reservoir (Phlegrean Fields)

Cioppi, D.; Ghelardoni, R.; Panci, G.; Sommaruga, C.; Verdiani, Giuseppe

doi:10.1007/978-94-009-9059-3_25

Cited by 3 publications

(5 citation statements)

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“…In particular, the measured temperatures indicate the existence of a huge magmatic body under the C.F. area [Cioppi et al, 1980;Carella and Guqlielminetti, 1983;Bruni et al, 1985]. This point will be further discussed in a subsequent section.…”

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confidence: 77%

Modeling of Surface Deformation in Volcanic Areas: The 1970–1972 and 1982–1984 Crises of Campi Flegrei, Italy

Bianchi

Coradini

Federico

et al. 1989

Collected Reprint Series

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Campi Flegrei is a densely inhabited volcanic area within a caldera, 12-14 km in diameter, immediately west of Naples, Italy. In 1970In -1972In and in 1982, Campi Flegrei experienced considerable ground surface deformation producing a bulge about 3.5 m high at its peak. In the two inflation episodes the point of maximum uplift did not change, coinciding with the caldera center, about which the displacements exhibited radial symmetry. The 1982-1984 uplift was accompanied by considerable seismic activity. Gravity changes have been interpreted as reflecting the occurrence of a subvertical magmatic intrusion. Volcanological, petrological, and geophysical data point to the existence of a shallow magma chamber just beneath the center of the caldera. We assume that the observed surface displacements are the response of an essentially elastic medium to a pressure increase in the magma chamber. Static deformation is calculated by using a finite-element method, assuming axial symmetry around a vertical axis through the caldera center. The role played by various components of the model, geometry, boundary conditions, elastic properties, is analyzed. It is shown that models assuming uniform elasticity are inadequate. Therefore the major volcanotectonic features as well as the influence of temperature and pressure on the elastic properties are taken into account. The results of various more complex models are presented. It is suggested that a progressively fractured zone, whose size and shape depend also on the possible occurrence of magmatic intrusions, may explain the observed surface displacements and the other data collected at Campi Flegrei. It is suggested that the 1970-1972 uplift was possibly accompanied by larger-scale changes in the stress field. INTRODUCTION Ground surface deformations in volcanic areas are usually interpreted to reflect changes of pressure in shallow magma reservoirs and/or the occurrence of intrusive events. Large deformations are often observed to occur in a very limited area, and their interpretation in terms of schematic models [Mogi, 1958; Dieterich and Decker, 1975] implies the assumption of unrealistically shallow chambers or intrusions and unreasonably large pressure increases [Walsh and Decker, 1971; Davis et al., 1974; Dieterich and Decker, 1975; Bianchi et al., 1984]. Therefore, more realistic models taking into account volcanological and structural features as well as the nonuniform response of country rocks (related to temperature and pressure gradients, possible fracturing, presence of fluids, etc.) are required. In the present paper, we shall proceed along this line, focusing our attention on the Campi Flegrei volcanic area. Campi Flegrei (C.F.) is a 35,000-year-old caldera, 12-14 km in diameter, located immediately west of Naples, Italy, in an area of regional tensional tectonics [Finetti and Morelli, 1974; Scandone, 1979]. In the last 10,000 years its activity has been characterized by a large number of explosive eruptions from different vents within the caldera. The most recen...

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confidence: 77%

Modeling of Surface Deformation in Volcanic Areas: The 1970–1972 and 1982–1984 Crises of Campi Flegrei, Italy

Bianchi

Coradini

Federico

et al. 1989

Collected Reprint Series

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“…In all cases, the first map refers to c = 0 and therefore represents the elastic solution. (Cioppi et al 1980). The pressure source model applies directly to the study of ground deformation in volcanic areas due to the presence of an insulated magma chamber where mechanisms of magma migration can provide a pressure increase on the surface of the chamber.…”

Section: Stress Fieldsmentioning

confidence: 99%

“…The presence of incoherent materials, such as volcanic products, and high temperatures typical of volcanic areas produces effective viscosities orders of magnitude lower than the characteristic values of the 'cold' Earth's crust, thus prompting one to take into account (Cioppi et al 1980). The pressure source model applies directly to the study of ground deformation in volcanic areas due to the presence of an insulated magma chamber where mechanisms of magma migration can provide a pressure increase on the surface of the chamber.…”

Section: Application To Volcanic Areasmentioning

confidence: 99%

Displacement and stress fields produced by a centre of dilation and by a pressure source in a viscoelastic half-space: application to the study of ground deformation and seismic activity at Campi Flegrei, Italy

Bonafede

Dragoni

Quareni

1986

Geophysical Journal International

156

129

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Analytical expressions for the static displacement field produced by a centre of dilation and by a pressure source in a viscoelastic half-space are derived. The associated stress fields are also computed. The rheology of a standard linear solid (SLS) is adopted for the shear modulus, while the incompressibility is kept elastic. An instantaneous dilation or variation of pressure is considered as responsible for the deformation. In the centre of dilation model, if the two rigidities of the SLS are of the same order of magnitude, the viscoelastic contribution to the deformation is negligible; if the short-term rigidity is at least two orders of magnitude higher than the other one, the results are indistinguishable from those obtained with a Maxwell solid rheology. In this case, it is found that the initial elastic displacement is amplified by 20 per cent. In the pressure source model, if the rigidities of the SLS are of the same order of magnitude, the initial elastic displacement is amplified by a factor of about 2, but unrealistically high pressure values are required. On the other hand, for a Maxwell solid rheology the displacement grows indefinitely in time, following a sudden application of a finite pressure. The uplift rate is evaluated and it is shown that, for obtaining values of the order of 1 m over one characteristic relaxation time, more reasonable values of pressure are allowed. Applications to ground deformation in volcanic areas are discussed, taking as an example the Campi Flegrei zone, near Naples, Italy.

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“…For example, the temperature at the interface between the magma chamber and the host rock can be estimated to be of the order of 1000°C at Campi Flegrei, according to Cioppi et al (1980).…”

Section: Discussion a N D Application To Campi Flegrei Italymentioning

confidence: 99%

“…Furthermore, within the caldera, the material surrounding the magma chamber is realistically endowed with an even lower rigidity, since the magma chamber is much hotter than the host rock. For example, the temperature at the interface between the magma chamber and the host rock can be estimated to be of the order of 1000°C at Campi Flegrei, according to Cioppi et al (1980). Model I1 takes into account that the magma is much hotter than the host rock, assuming that the rigidity in the surrounding of the magma chamber is lower than the calderic rigidity, which in turn is lower than the crustal, outer rigidity.…”

Section: Campi Flegrei Italymentioning

confidence: 99%

Finite element deformation of an elastic, non-uniform medium produced by a dilating or pressurized magma chamber

Quareni¹

1990

Geophysical Journal International

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SUMMARY Vertical and horizontal ground deformations accompanied by seismic activity are typical features of volcanic areas within quiescent calderas such as Long Valley Caldera (California), Yellowstone (Wyoming), Rabaul (Papua New Guinea) and Campi Flegrei (Italy). Ground deformation can be related to the existence of a shallow pressurized magma chamber. Migration processes of hot pressurized fluids are also responsible for the observed uplift. A finite element model is derived and the solutions are checked against the analytical deformation field due to a pressurized, spherical cavity embedded in an infinite, homogeneous, elastic space. The effects related to the finite size of the magma chamber buried in a half‐space are investigated and compared with the analytical results obtained for a point‐like deformation source. In the latter case, a dilation or an overpressure at the source are equivalent in terms of ground displacement, while in the former the choice of the boundary condition at the magma chamber walls (fixed displacement, i.e. dilation, or pressure) is found to be crucial. A pressurized shallow magma chamber produces a larger (even of a factor of two) ground deformation than a point‐like source located at the same depth. This effect can be explained by the existence of a free surface towards which the medium is allowed to deform more easily. Finally, lateral and vertical variations of the rigidity are taken into account and it is shown how they can affect the solution: modelling the caldera as a low‐rigidity zone, much larger ground displacement can be obtained. The results obtained help to overcome one of the major problems so far encountered in the interpretation of the ground deformation in quiescent calderas with point‐like source models: the need for unreasonably high overpressures in order to produce the observed uplift.

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Demonstration Project: Evaluation of The Mofete High Enthalpy Reservoir (Phlegrean Fields)

Cited by 3 publications

References 1 publication

Modeling of Surface Deformation in Volcanic Areas: The 1970–1972 and 1982–1984 Crises of Campi Flegrei, Italy

Modeling of Surface Deformation in Volcanic Areas: The 1970–1972 and 1982–1984 Crises of Campi Flegrei, Italy

Displacement and stress fields produced by a centre of dilation and by a pressure source in a viscoelastic half-space: application to the study of ground deformation and seismic activity at Campi Flegrei, Italy

Finite element deformation of an elastic, non-uniform medium produced by a dilating or pressurized magma chamber

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