179 research outputs found
Finite element modeling of ground deformation and gravity field at Mt. Etna
An elastic 3-D axi-symmetric model based on Finite Element Method (FEM) is proposed to compute ground deformation
and gravity changes caused by overpressure sources in volcanic areas. The numerical computations
are focused on the modeling of a complex description of Mt Etna in order to evaluate the effect of topography,
medium heterogeneities and source geometries. Both ground deformation and gravity changes are investigated
by solving a coupled numerical problem considering a simplified ground surface profile and a multi-layered
crustal structure inferred from seismic tomography. The role of the source geometry is also explored taking into
account spherical and ellipsoidal volumetric sources. The comparison between numerical results and those
predicted by analytical solutions disclosed significant discrepancies. These differences constrain the applicability
of simple spherical source and homogeneous half-space hypotheses, which are usually implicitly assumed
when analytical solutions are applied
New data from borehole strainmeters to infer lava fountain sources (Etna 2011-2012)
In January 2011 eruptive activity resumed at Etna producing a new phase with frequent lava fountain episodes until April 2012. In November 2011, the first two borehole strainmeters were installed, which detected negative strain changes (~ 0.15 - 0.8 strain) during the paroxysmal events. A Finite Element Model was set up to estimate accurately the tilt and volumetric strain, taking into account the real profile of the volcano and the elastic medium heterogeneity. The numerical computations indicated an elongated depressurizing source located at 0 km b.s.l., which underwent a volume change of ~2 x 106 m3 which is the most of the magma volume erupted while a smaller remaining part is accommodated by the magma compressibility. This shallow source cannot accumulate large magma volumes and, thus, favours short term periodic eruptive events with a fairly constant balance between the refilling and the erupted magma
Integrated inversion of ground deformation and magnetic data at Etna volcano using a genetic algorithm technique
Geodetic and magnetic investigations have been playing an increasingly important role in studies on Mt. Etna
eruptive processes. During ascent, magma interacts with surrounding rocks and fluids, and inevitably crustal deformation
and disturbances in the local magnetic field are produced. These effects are generally interpreted separately
from each other and consistency of interpretations obtained from different methods is qualitatively
checked only a posteriori. In order to make the estimation of source parameters more robust we propose an integrated
inversion from deformation and magnetic data that leads to the best possible understanding of the underlying
geophysical process. The inversion problem was formulated following a global optimization approach based
on the use of genetic algorithms. The proposed modeling inversion technique was applied on field data sets
recorded during the onset of the 2002-2003 Etna flank eruption. The deformation pattern and the magnetic anomalies
were consistent with a piezomagnetic effect caused by a dyke intrusion propagating along the NE direction
fem and ann combined approach for predicting pressure source parameters at etna volcano
Abstract. A hybrid approach for forward and inverse geophysical modeling, based on Artificial Neural Networks (ANN) and Finite Element Method (FEM), is proposed in order to properly identify the parameters of volcanic pressure sources from geophysical observations at ground surface. The neural network is trained and tested with a set of patterns obtained by the solutions of numerical models based on FEM. The geophysical changes caused by magmatic pressure sources were computed developing a 3-D FEM model with the aim to include the effects of topography and medium heterogeneities at Etna volcano. ANNs are used to interpolate the complex non linear relation between geophysical observations and source parameters both for forward and inverse modeling. The results show that the combination of neural networks and FEM is a powerful tool for a straightforward and accurate estimation of source parameters in volcanic regions
Multifractality in local geomagnetic field at Etna volcano, Sicily (southern Italy)
International audienceWe applied the Multifractal Detrended Fluctuation Analysis (MF-DFA), which allows to detect multifractality in nonstationary signals, to the hourly means of local geomagnetic field recorded at Mt. Etna volcano (southern Italy). We studied the signal measured at one geomagnetic station, installed at the summit of volcano, which was characterized by a strong eruption on 27 October 2002. We analyzed two frames of signals, one measured before the eruption and the other after, in order to evaluate dynamical changes induced by the eruptive event. Our findings show that: i) the geomagnetic time series is multifractal; ii) the multifractal degree of the signal decreases after the occurrence of eruption. This study aims to propose another approach to investigate the complex dynamics of volcano-related geomagnetic field
Inverse modeling in geophysical applications
The interpretation of the potential ¯eld data is an useful tool that allows for
both investigating the subsurface structures and providing a quantitative evalu-
ation of the geophysical process preceding and accompanying period of volcanic
unrest. Potential ¯eld inversion problem are required to combine forward mod-
els with appropriate optimization algorithms and automatically ¯nd the best
set of parameters that well matches the available observations. Indeed, investi-
gations on the mathematical equations to be inverted, have revealed that these
models are ill-posed and highly non-linear. Numerical methods for modeling
potential ¯eld observations are proposed and applied on real dataset
Non-linear analysis of geomagnetic time series from Etna volcano
An intensive nonlinear analysis of geomagnetic
time series from the magnetic network on Etna volcano was
carried out to investigate the dynamical behavior of magnetic
anomalies in volcanic areas. The short-term predictability of
the geomagnetic time series was evaluated to establish a possible
low-dimensional deterministic dynamics. We estimated
the predictive ability of both a nonlinear forecasting technique
and a global autoregressive model by comparing the
prediction errors. Our findings highlight that volcanomagnetic
signals are the result of complex processes that cannot
easily be predicted. There is slight evidence based on
nonlinear predictions, that the geomagnetic time series are to
be governed by many variables, whose time evolution could
be better regarded as arising from complex high dimensional
processes
FEM and ANN combined approach for predicting pressure source
A hybrid approach for forward and inverse geophysical
modeling, based on Artificial Neural Networks
(ANN) and Finite Element Method (FEM), is proposed in
order to properly identify the parameters of volcanic pressure
sources from geophysical observations at ground surface.
The neural network is trained and tested with a set of
patterns obtained by the solutions of numerical models based
on FEM. The geophysical changes caused by magmatic pressure
sources were computed developing a 3-D FEM model
with the aim to include the effects of topography and medium
heterogeneities at Etna volcano. ANNs are used to interpolate
the complex non linear relation between geophysical observations
and source parameters both for forward and inverse
modeling. The results show that the combination of
neural networks and FEM is a powerful tool for a straightforward
and accurate estimation of source parameters in volcanic
regions
Volcanomagnetic Evidence of the Magmatic Intrusion on 13th May 2008
During the onset of 2008 volcanic crisis at Mt Etna, the near-real time magnetic data provided a continuous updating of the volcano activity state on the northern flank. On the morning of 13th May 2008, significant local magnetic field changes marked the resumption of the eruptive activity characterized by the opening of a fracture field on the northern flank, and an eruptive fissure in the Valle del Bove. In agreement with the northward propagation of seismic events, magnetic signals at 5 stations in the summit area revealed a nearly NNW-SSE oriented magmatic intrusion, which started at about 9:00 GMT, propagated northward for about 2 km, and stopped at 14:00 GMT before reaching the North-East Rift. Magnetic variations, with amplitude ranging between 1.8 nT and -6.5 nT, are consistent with those calculated from piezomagnetic models, where stress-induced changes in rock magnetization are produced by the magmatic intrusion
Modeling of ALOS and COSMO-SkyMed satellite data at Mt Etna: implications on relation between seismic activation of the Pernicana fault system and volcanic unrest
We investigate the displacement induced by the 2–3 April 2010 seismic swarm (the largest event being of Ml
4.3 magnitude) by means of DInSAR data acquired over the volcano by the Cosmo-SkyMed and ALOS radar
systems. Satellite observations, combined with leveling data, allowed us to perform a high-resolution modeling
inversion capable of fully capturing the deformation pattern and identifying the mechanism responsible
for the PFS seismic activation. The inversion results well explain high gradients in the radar line of sight displacements
observed along the fault rupture. The slip distribution model indicates that the fault was characterized
by a prevailing left-lateral and normal dip–slip motion with no fault dilation and, hence, excludes that
the April 2010 seismic swarm is a response to accommodate the stress change induced by magma intrusions,
but it is due to the tectonic loading possibly associated with sliding of the eastern flank of the volcano edifice.
These results provide a completely different scenario from that derived for the 22 September 2002 M3.7
earthquake along the PFS, where the co-seismic shear-rupture was accompanied by a tensile mechanism
associated with a first attempt of magma intrusion that preceded the lateral eruption occurred here a
month later. These two opposite cases provide hints into the behavior of the PFS between quiescence and unrest
periods at Etna and pose different implications for eruptive activity prediction and volcano hazard assessment.
The dense pattern of ground deformation provided by integration of data from short revisiting
time satellite missions, together with refined modeling for fault slip distribution, can be exploited at different
volcanic sites, where the activity is controlled by volcano-tectonic interaction processes, for a timely evaluation
of the impending hazards
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