Publication Date:
2020-12-14
Description:
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.
Description:
Published
Description:
2V. Dinamiche di unrest e scenari pre-eruttivi
Description:
JCR Journal
Description:
open
Keywords:
hydrothermal process
;
deformation
;
gravity changes
;
05. General::05.05. Mathematical geophysics::05.05.99. General or miscellaneous
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
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