Deformation and stress in hydrothermal regions: The case of a disk-shaped inclusion in a half-space

Mantiloni, Lorenzo; Nespoli, Massimo; Belardinelli, Maria Elina; Bonafede, Maurizio

doi:10.1016/j.jvolgeores.2020.107011

Cited by 12 publications

(16 citation statements)

References 51 publications

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“…Caldera volcanoes often cover a wide geographical area (up to several ten of kilometers wide) with large, geometrically complex and heterogeneous magmatic systems that are capable of producing explosive eruptions, sometimes of great size. However, understanding of the current state of these systems is often made complex by the presence of active, shallower hydrothermal systems and fault structures (e.g., Sandri et al, 2017;Mantiloni et al, 2020). Disentangling the signals of magmatic unrest (e.g., variations in the pressure of the system due to magma recharge or ascent) vs. non-magmatic unrest (e.g., changes in the hydrothermal system or tectonic earthquakes) can be difficult, with the potential for many different mechanisms that can produce similar unrest symptoms (Acocella et al, 2015).…”

Section: Introductionmentioning

confidence: 99%

Earthquake Analysis Suggests Dyke Intrusion in 2019 Near Tarawera Volcano, New Zealand

et al. 2021

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Tarawera volcano (New Zealand) is volumetrically dominated by rhyolitic lavas and pyroclastic deposits, but the most recent event in AD 1886 was a basaltic Plinian fissure eruption. In March 2019 a swarm of at least 64 earthquakes occurred to the NE of Tarawera volcano, as recorded by the New Zealand Geohazard Monitoring Network (GeoNet). We use seismological analysis to show that this swarm was most likely caused by a dyke that intruded into the brittle crust between depths of 8–10 km and propagated toward Tarawera volcano for 2 km at a rate of 0.3–0.6 m s−1. We infer that this was a dyke of basaltic composition that was stress-guided toward Tarawera volcano by the topographic load of the volcanic edifice. Dyke intrusions of this nature are most likely a common occurrence but a similar process may have occurred during the 1886 eruption with a dyke sourced from some lateral distance away from the volcano. The 2019 intrusion was not detected by InSAR geodesy and we use synthetic models to show that geodetic monitoring could only detect a ≥6 m wide dyke at these depths. Improvements to geodetic monitoring, combined with detailed seismological analysis, could better detect future magmatic intrusions in the region and serve to help assess ongoing changes in the magmatic system and the associated possibilities of a volcanic event.

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Section: Introductionmentioning

confidence: 99%

Earthquake Analysis Suggests Dyke Intrusion in 2019 Near Tarawera Volcano, New Zealand

et al. 2021

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“…Of course, the models presented above are applicable to deep TPE sources, that is having depths greater than the lateral extent, since the effects due to the proximity of the free surface cannot be obtained using the present method based on a displacement potential, because the Green's function in a half-space is no longer symmetric and eqs (10)-( 12) no longer hold. Nevertheless, for a horizontal TPE disc in a half-space bounded by a free surface, Mantiloni et al (2020) showed that semi-analytic solutions can be obtained separating Mindlin's Green's function (Mindlin 1936) into a singular component, the explicit expressions of which are provided in the present paper, and a regular 1. Green lines separate zones where normal faulting is favoured, from the ones of thrust faulting, as also reported.…”

Section: Discussionmentioning

confidence: 78%

“…Another important result, valid in an unbounded medium, is that a simplified diffusion equation may be obtained for the pore pressure, formally independent from stress, as already noted by Shapiro (2015) and Wang (2017). Neglecting the presence of the free surface may appear unrealistic but Mantiloni et al (2020) provided semi-analytical solutions for a disc-shaped TPE source in a homogeneous halfspace as the sum of different terms, showing that the term which describes the effect of a TPE disc embedded within an unbounded medium is dominant close to and within the disc.…”

Section: Introductionmentioning

confidence: 82%

“…( 71) well approximates the total stress even in the presence of a free surface. Differently from Mantiloni et al (2020), in the present model the external stress field is entirely deviatoric, as due to the absence of the free surface condition and this allows writing kk = 1 , leading to a simpler pressure diffusion equation. As in Belardinelli et al (2019), in the far field, displacements and stresses are asymptotically equal (within a multiplicative factor) to those provided by a pressurized spherical cavity.…”

Section: Discussionmentioning

confidence: 99%

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Stress changes caused by exsolution of magmatic fluids within an axisymmetric inclusion

Belardinelli

Nespoli

Bonafede

2022

Geophysical Journal International

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Summary In volcanic regions ascending magma is subject to depressurization and is generally accompanied by exsolution of volatiles. We blackassume a process in which these volatiles propagate upward across newly fractured and permeable rock layers, bringing a sharp increase of pore pressure and temperature within a thin disk-shaped region (inclusion). Thermo-poro-elastic (TPE) inclusion models provide a mechanism to explain seismicity and deformation induced by p and T changes in absence of new magma emplacement in volcanic contexts. They are also suitable to represent the mechanical effects due to fluid extraction and re-injection in geothermal fields. In the present work analytic solutions are provided for the displacement, strain and stress fields assuming a thermo-poro-elastic unbounded medium. Significant deviatoric stress is generated by positive increments of pore pressure and temperature: the stress field is fully deviatoric outside the TPE inclusion, but a strong isotropic stress component is present within, leading to highly heterogeneous faulting mechanisms: if the disk plane is horizontal, thrust faulting mechanisms are favoured within the TPE disk over optimally oriented faults and normal mechanisms above. The model is easily generalized to a vertically thick disk with variable temperature and pore-pressure changes: then, an extensional environment can be obtained even within the TPE inclusion assuming upward decreasing of pore pressure and temperature changes. The supplied analytical solution may be used to model near-field TPE inclusion effects and to validate more complex numerical modelling.

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“…Magma emplacement deforms the crust resulting in surface uplift or subsidence signals that can be measured and used to infer information about intrusion depth, volume, shape and orientation, and which may be useful for determining potential eruption characteristics (Geshi et al, 2020). However, the vast majority of models used in volcano monitoring to infer the deformation associated with magmatic emplacement assume that the crust is either isotropic (an elastic half-space) (e.g., Okada, 1985;Mantiloni et al, 2020), or mechanically stratified with horizontal layers (Masterlark, 2007;Bazargan and Gudmundsson, 2019;2020). Both assumptions are likely simplifications, especially in areas where volcanoes are built atop highly folded and deformed rocks, such as in Cordillera settings (Clunes et al, 2021).…”

Section: Introductionmentioning

confidence: 99%

Inclination and heterogeneity of layered geological sequences influence dike-induced ground deformation

Clunes¹,

Browning²,

Marquardt³

et al. 2022

Preprint

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Constraints on the amount and pattern of ground deformation induced by dike emplacement are important for assessing potential eruptions. The vast majority of ground deformation inversions made for volcano monitoring during volcanic unrest assume that dikes are emplaced in either an elastic-half space (a homogeneous crust) or a crust made of horizontal layers with different mechanical properties. Here, we extend these models by designing a novel set of two-dimensional Finite Element Method numerical simulations that consider dike-induced surface deformations related to a mechanically heterogeneous crust with inclined layers, thus modelling a common geometry in stratovolcanoes and crustal segments that have been folded by tectonic forces. Our results confirm that layer inclination can produce localized ground deformations which may be up to 40 times higher in terms of deformation magnitude than would be expected in a non-layered model, depending on the angle of inclination and the stiffness of the rock units that host, and are adjacent to the dike. Generated asymmetrical deformation patterns produce deformation peaks located as much as 1.4 km away from those expected in non-layered models. These results highlight the necessity to accurately quantify both the mechanical properties and attitude of the geology underlying active volcanoes.

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Deformation and stress in hydrothermal regions: The case of a disk-shaped inclusion in a half-space

Cited by 12 publications

References 51 publications

Earthquake Analysis Suggests Dyke Intrusion in 2019 Near Tarawera Volcano, New Zealand

Earthquake Analysis Suggests Dyke Intrusion in 2019 Near Tarawera Volcano, New Zealand

Stress changes caused by exsolution of magmatic fluids within an axisymmetric inclusion

Inclination and heterogeneity of layered geological sequences influence dike-induced ground deformation

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