322,952 research outputs found
Electrical signatures of a permeable zone in carbonates hosting local geothermal manifestations: Insights for the deep fluid flow in the gargano area (South-eastern Italy)
No full textIn northern Apulia (Italy), geothermal evidence can be associated to structural conditions. The area is characterised by a thick calcareous and dolomitic succession, affected by seismogenic faults and karst dissolution, and by the presence of some surficial geothermal pieces of evidence (coastal springs and well waters). In order to contribute to a better understanding of the deep circulation, an audio-magnetotelluric (AMT) survey was carried out. Soundings were acquired at 22 sites along a 27-km long profile crosscutting the Gargano Promontory and the Tavoliere Plain. A 2D inversion was undertaken providing a resistivity model down to 3 km b.s.l.. In the Tavoliere Plain the resistivity mainly increases with depth. Towards the Gargano area, a low-resistivity layer is interpreted as a fracture network which may favour fluid circulation. The supposed geometry of the permeable zone matches well with the structural interpretation proposed by independent studies. Thus, the present AMT study enabled imaging the first order geological structures that channel deep fluids as locally recognised by boreholes and natural manifestations at the surface
A method to determine the magnetotelluric static shift from DC resistivity measurements in practice
No full textMany efforts have been made to face magnetotelluric (MT) static shift. Impedance tensor analyses give insight to the presence of this feature and allow the determination of some parameters described by the MT distortion matrix. A quantitative determination of the full distortion matrix is, however, still difficult and needs additional measurements. In addition to MT, other electric and electromagnetic methods also are effected by static shift. Using direct current resistivity techniques, e.g., we can determine the static-shift factors in a simpler way because the sources can be controlled. Generally, because the distortion matrix has four entries, four additional quantities have to be determined to describe the static shift completely. They can be achieved, e.g., through measuring two orthogonal electric field components for two orthogonal source configurations. The source electrode spacing, however, has to be sufficiently large to resemble horizontal currents and match the MT plane-wave analog. The procedure at hand extracts the static-shift factors from multielectrode measurements after this condition is met. For the sake of simplicity and demonstration purposes, only inline measurements orthogonal to the strike direction of a 2D model are considered so that the vectorial problem reduces to a scalar one. This procedure is applied to a MT field data set in a regional 2D environment that shows only two additional quantities are necessary to determine the static shift
Surface investigation of lubricant-metal interactions by synchrotron photoemission spectroscopy
No full textGranger causality analysis of geophysical, geodetic and geochemical observations during volcanic unrest: A case study in the campi flegrei caldera (Italy)
Get PDFThe recent signs of reawakening at Campi Flegrei caldera (Southern Italy) received a great deal of attention due to the issues related to the volcanic risk management in a densely populated area. This paper explores relations between ground deformations, seismicity and geochemical time series in the time span 2004–2016. The aim is to unravel primary processes of unrest and the related indicators which may change in time. Data structure and interactions among variables were examined applying the clustering analysis, the correlations and the Granger causality test. The hierarchical agglomerative clustering detected two sub-periods which were further investigated. In both sub-period causal links were observed between variables while correlations did not appear and vice versa. Thus, well established formal approaches are required to study causal relations. Granger test results indicate that during 2004–2011 the awakening unrest could be mainly ascribed to hydrothermal system pressure fluctuations, probably induced by deep-rooted fluids injection, and that ground deformation together with CO2 /H2 O appears the most suitable geo-indicators. The 2011–2016 sub-period is characterized by enhanced dynamical connectivity. Granger test results suggest that the unrest is driven by a more localized and shallower thermohydromechanical engine. CO/CO2, He/CH4 and ground deformation velocity are mutually interacting appearing the most suitable geo-indicators
Correlation between resistivity and seismicity at Etna volcano (Italy)
No full textA great number of studies concerning the existence of instability phenomena as eastward sliding movements,
in the eastern flank of Etna (Italy) have been performed. Actually, although the existence of these phenomena
is overt, clear results about the presence in depth of décollement surfaces are still lacking. Multi-disciplinary
information must be put together in order to better constrain modeling. A magnetotelluric (MT) derived 2D
resistivity models recovered along two profiles (N-S and NW-SE-striking) located in the eastern flank of Etna and
a well-localized seismicity data set belonging to the period July 2001- December 2006 are herein jointly analysed.
The comparison between the seismicity data set and the MT results, both strike analysis and the resistivity models,
was performed.
Detailed MT strike and dimensionality analyses reveal consistent, but period dependent, strike directions,
indicating a change in the geoelectrical strike with period, that means, giving their direct proportionality, with
depth. In the period ranges 0.01-1 s and 4-100 s the geoelectric strike angle is oriented W-E and almost SW-NE,
respectively. A comparison with seismological data indicates that shallower MT strike is consistent with the EW
clustered seismicity along the Pernicana Fault System.
Projection of the seismic activity located within a
2 km wide band, centered on the two MT resistivity models,
strengths the existence of two different processes affecting the eastern flank at the same time, but at different depth
ranges. The boundary between them, is marked by a resistivity increasing, that is interpreted as the top of the Etna
basement. Within the second depth range (3-7 km bsl) along the MT profile, a detailed analysis of the relative
seismic events recovered a low seismicity level at 4.5
0.3 km b.s.l.. A 3D inspection of the seismic dataset
shows that this level of reduced seismicity clearly originates from the northern wall of VdB and extends to NE.
This result suggests that the deeper rupture process characterizing the north-eastern flank of Etna may occurs on
multiple planes and the level of reduced seismicity could play a key role in the instability processes involving the
eastern flank of the volcano
Influenza dell'altitudine e della specie su alcuni parametri ematici e valori biochimici del siero di sangue in camelidi sudamericani
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Space-time analysis of informational properties of GPS time series recorded at the Campi Flegrei caldera (Italy)
Get PDFIn this work the time dynamics of GPS time series recorded at the Campi Flegrei caldera from 2000 to 2019 was investigated by using the Fisher Information Measure (FIM) and the Shannon entropy power (SEP), two infor-mational methods that allow the detection of changes in the dynamical behavior of a complex system, like the volcanic one, quantifying respectively the order/organization and the disorder/uncertainty. By jointly analyzing the FIM and the SEP through the Fisher-Shannon Information Plane (FSIP) it was shown that the SEP discrim-inates quite well the vertical displacement time series, while the FIM discriminates better the horizontal ones, which are featured by a more complex behavior. Globally, the most striking change in the SEP is found in 2012, while at local scale abrupt loss of order (indicated by low values of FIM) well correlate with the occurrence of seismic swarms. A further informational quantity, the complexity C (given by the product between SEP and FIM), has been revealed to be sensitive to the baseline deformation level increases and to the small-amplitude mod-ulation of deformation signals within the caldera
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