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- Title
Thermo‐Hydro‐Mechanical Model and Caprock Deformation Explain the Onset of an Ongoing Seismo‐Volcanic Unrest.
- Authors
Akande, Waheed Gbenga; Gan, Quan; Cornwell, David G.; De Siena, Luca
- Abstract
Modeling seismicity at volcanoes remains challenging as the processes that control seismic energy release due to fluid transport, heat flow, and rock deformation are firmly coupled in complex geological media. Here, we couple fluid‐flow and mechanical (deformation) simulators (TOUGHREACT–FLAC3D) to reproduce fluid‐induced seismicity at Campi Flegrei caldera (southern Italy) in isothermal (HM) and nonisothermal (THM) conditions. The unique ability of the Campi Flegrei caprock to withstand stress induced by hot‐water injections is included in the model parametrization. After pore pressure accumulation is guided by a combination of thermal and hydromechanical interactions, contrasting compressive and extensional forces act on the basal and top parts of the caprock, respectively. Then, pressure perturbation and caprock deformation induce fractures that allow hot fluids uprising to pressurize the overlying fault, driving it toward failure and triggering seismicity. Under similar mechanical boundary conditions, the induced thermal effects prompt seismic slip earlier but with higher seismic magnitudes when (1) thermal equilibrium is preserved and (2) the thermal contrast is enhanced due to increased fluid injection temperatures. The results indicate that numerical models of volcano seismicity must consider the influence of rock‐sealing formations to obtain more robust, accurate, and realistic seismic predictions at volcanoes. The proposed models satisfactorily reproduce the magnitude–depth distribution of the swarm (October 5, 2019), preceding the two strongest earthquakes recorded in 35 years at the caldera (3.1 and 3.3—on December 6, 2019, and April 26, 2020, respectively) using hot‐water injection from depth. Plain Language Summary: Can we model seismicity in a volcanic caldera using tools and methods taken from deformation and fluid‐flow modeling in reservoirs? If the target is Campi Flegrei (southern Italy) the application must certainly include parameter such as the recently characterized "caprock," which partially mitigates the stress induced by dyke intrusions and fluid injections during deformation unrests. Through the coupling of mechanical and fluid‐flow simulators, we targeted the seismic response of the caldera to hot‐water injections in order to reproduce the strongest seismic unrest in the last 35 years (2019–2020). The results show that hot‐water injections can reproduce the depth–magnitude trend at the start of the unrest in isothermal conditions, especially if the temperature of the injections increases. Including rock‐sealing formations in the modeling of seismic unrest at this and other volcanoes is vital to understand seismic precursors and hazard. In order to model the strongest seismicity, the effect of either magma or magmatic fluids must likely be included in the modeling. Key Points: Injection‐induced caprock deformation is a major controlling parameter of seismicity at Campi Flegrei calderaThe seismo‐volcanic unrests are thermally driven but hydromechanical in natureHot‐water injections modulated by injection rate and temperature, caprock and fault permeabilities, reproduce the swarm at the onset of the unrest
- Subjects
PHLEGRAEAN Plain (Italy); HEAT flow (Oceanography); DEFORMATIONS (Mechanics); CALDERAS; MAGMAS
- Publication
Journal of Geophysical Research. Solid Earth, 2021, Vol 126, Issue 3, p1
- ISSN
2169-9313
- Publication type
Article
- DOI
10.1029/2020JB020449