Denoising gravity and geomagnetic signals from Etna volcano (Italy) using multivariate methods

Abstract. Multivariate methods were applied to denoise the gravity and geomagnetic signals continuously recorded by the permanent monitoring networks on the Etna volcano. Gravity and geomagnetic signals observed in volcanic areas are severely influenced by meteorological variables (i.e. pressure, temperature and humidity), whose disturbances can make the detection of volcanic source effects more difficult. For volcano monitoring it is necessary, therefore, to reduce the effects of these perturbations. To date filtering noise is a very complex problem since the spectrum of each noise component has wide intervals of superposition and, some times, traditional filtering techniques provide unsatisfactory results. We propose the application of two different approaches, the adaptive neuro-fuzzy inference system (ANFIS) and the Independent Component Analysis (ICA) to remove noise effects from gravity and geomagnetic time series. Results suggest a good efficiency of the two proposed approaches since they are capable of finding and effectively representing the underlying factors or sources, and allow local features of the signal to be detected

Denoising gravity and geomagnetic signals from Etna volcano (Italy)

Multivariate methods were applied to denoise the gravity and geomagnetic signals continuously recorded by the permanent monitoring networks on the Etna volcano. Gravity and geomagnetic signals observed in volcanic areas are severely influenced by meteorological variables (i.e. pressure, temperature and humidity), whose disturbances can make the detection of volcanic source effects more difficult. For volcano monitoring it is necessary, therefore, to reduce the effects of these perturbations. To date filtering noise is a very complex problem since the spectrum of each noise component has wide intervals of superposition and, some times, traditional filtering techniques provide unsatisfactory results. We propose the application of two different approaches, the adaptive neuro-fuzzy inference system (ANFIS) and the Independent Component Analysis (ICA) to remove noise effects from gravity and geomagnetic time series. Results suggest a good efficiency of the two proposed approaches since they are capable of finding and effectively representing the underlying factors or sources, and allow local features of the signal to be detected

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

Vectorial magnetometers for noise reduction in volcanomagnetic monitoring at Mt Etna

The volcanomagnetic monitoring is critically dependent on the ability to detect and isolate magnetic variations related to volcanic activity. Accurate detection of volcanomagnetic anomalies attributable to the volcano’s dynamics requires removing from measurements of the earth’s magnetic field, fluctuations of external origin which may be up to hundreds of nanotesla during geomagnetic storms. The commonly used method of taking simple differences of the total intensity with respect to the simultaneous value at a remote reference is partially successful. Variations in the difference fields arise principally from contrasting electromagnetic properties at magnetometer sites. To improve the noise reduction of geomagnetic data from magnetic network of Mt Etna we developed an adaptive filtering. Magnetic vector data are included as input to the filter, to account for the orientation of the disturbance field. The filter is able to estimate and rectify the model parameters continuously by means of new observations, so that predictions match the observed data. The error of state estimation has been decreased and the filtering accuracy improved. Experimental data collected on Mt Etna during 2010 are analyzed to relate the field variation at a given station to the field at other sites filtering out undesired noise and enhancing signal-to-noise ratio

Seismic-induced accelerations detected by two parallel gravity meters in continuous recording with a high sampling rate at Etna volcano

We analyse a microgravity data set acquired from two spring LaCoste & Romberg gravity meters operated in parallel at the same site on Etna volcano (Italy) for about two months (August – September 2005). The high sampling rate acquisition (2Hz) allowed the correlation of short-lasting gravity fluctuations with seismic events. After characterizing the oscillation behavior of the meters, through the study of spectral content and the background noise level of both sequences, we recognized fluctuations in the gravity data, spanning a range of periods from 1 second to about 30 seconds dominated by components with a period of about 15 ÷ 25 seconds, during time intervals encompassing both local seismic events and large worldwide earthquakes. The data analyses demonstrate that observed earthquake-induced gravity fluctuations have some differences due to diverse spectral content of the earthquakes. When local seismic events which present high frequency content excite the meters, the correlation between the two gravity signals is poor (factor < 0.3). Vice versa, when large worldwide earthquakes occur and low frequency seismic waves dominate the ensuing seismic wavefield, the resonance frequencies of the meters are excited and they react according to more common features. In the latter case, the signals from the two instruments are strongly correlated to each other (up to 0.9). In this paper the behaviors of spring gravimeters in the frequency range of the disturbances produced by local and large worldwide earthquakes are presented and discussed

Mendelian Randomization using Public Data from Genetic Consortia.

Mendelian randomization (MR) is a technique that seeks to establish causation between an exposure and an outcome using observational data. It is an instrumental variable analysis in which genetic variants are used as the instruments. Many consortia have meta-analysed genome-wide associations between variants and specific traits and made their results publicly available. Using such data, it is possible to derive genetic risk scores for one trait and to deduce the association of that same risk score with a second trait. The properties of this approach are investigated by simulation and by evaluating the potentially causal effect of birth weight on adult glucose level. In such analyses, it is important to decide whether one is interested in the risk score based on a set of estimated regression coefficients or the score based on the true underlying coefficients. MR is primarily concerned with the latter. Methods designed for the former question will under-estimate the variance if used for MR. This variance can be corrected but it needs to be done with care to avoid introducing bias. MR based on public data sources is useful and easy to perform, but care must be taken to avoid false precision or bias

Magnetic features of the magmatic intrusion occurred in 2007 eruption at Stromboli Island (Italy.)

Significant changes in the local magnetic field marked the resumption of the eruptive activity at Stromboli volcano on February 27, 2007. After differential magnetic fields were filtered from the external noise by adaptive filters and from the seasonal thermic noise using temperature data, we highlighted step-like changes of 1-4 nT coincident with the eruptive fissures opening in the upper part of the Sciara del Fuoco. The magnetic variations detected at 2 stations are closely related to the propagation of a shallow NE-SW magmatic intrusion outside the summit craters area . These observations are consistent with those calculated from piezomagnetic models, where stress-induced changes in rock magnetization are produced by the magmatic intrusion. No significant magnetic changes were observed when the first fractures opened along the NE crater rim. Indeed, the stress-induced magnetization caused by this magmatic activity is expected to be too low because of the structural weakness and/or thermal state of the summit area. The continuous long-term decay characterizing the post-eruptive magnetic pattern was related to a time-dependent relaxation process. A Maxwell rheology was assumed and the temporal evolution of the piezomagnetic field was evaluated. This allowed for the estimate of the rheological properties of the medium, in particular an average viscosity ranging between 1016 and 1017 Pas was achieved involving a relaxation time τ of about 38 days

Magma storage, eruptive activity and flank instability: inferences from ground deformation and gravity changes during the 1993-2000 recharging of Mt. Etna volcano

A long recharging period characterized Mount Etna volcano during 1993-2000 before the main explosive-effusive 2001 and 2002-03 flank eruptions. The joint analysis of ground deformation and gravity data over this entire period revealed that different phenomena occurred within Etna's plumbing system and clearly inferred two phases spanning 1993-97 and 1994-2000, respectively. The first phase was characterized by magma storage and accumulation at an intermediate depth (2-6 km below sea level), which provoked an overall inflation and positive gravity changes. During the second phase, the magma started to rise and intrude at shallower levels favouring the movement of the unstable eastern flank, which accelerated its sliding toward the East. The shallower magma accumulation also caused the gas exolution, associated with increasing explosive activity at the summit craters, detected by a gravity negative variation. The gravity measurements, independently of the same result obtained by geochemical studies, confirm that only 20-30% of the magma volumes supplied in the plumbing system were then erupted. The complex dynamic of rising magma beneath Mount Etna makes ground deformation and gravity measurements complementary, being able to detect different effects of magma emplacements beneath the surface. Our results also highlight how the joint use of ground deformation and gravity observations may be crucial in identifying the nature and rate of an impending season of volcanic eruptions

A prototype of a large tunable Fabry–Pérot interferometer for solar spectroscopy

Large Fabry-Pérot Interferometers (FPIs) are used in a variety of astronomical instrumentation, including spectro-polarimeters for 4 m class solar telescopes. In this work we comprehensively characterize the cavity of a prototype 150 mm FPI, sporting a novel, fully symmetric design. Of particular interest, we define a new method to properly assess the gravity effects on the interferometer's cavity when the system is used in either the vertical or horizontal configuration, both typical of solar observations. We show that the symmetric design very effectively limits the combined effects of pre-load and gravity forces to only a few nm over a 120 mm diameter illuminated surface, with gravity contributing ~2 nm peak-to-valley (~0.3 nm rms) in either configuration. We confirm a variation of the tilt between the plates of the interferometer during the spectral scan, which can be mitigated with appropriate corrections to the spacing commands. Finally, we show that the dynamical response of the new system fully satisfies typical operational scenarios. We conclude that large, fully symmetric FPIs can be safely used within solar instrumentation in both, horizontal and vertical position, with the latter better suited to limiting the overall volume occupied by such an instrument

Hydrocortisone malabsorption due to polyethylene glycols (Macrogol 3350) in a girl with congenital adrenal insufficiency.

BACKGROUND: Primary adrenal insufficiency is relatively rare in children and, if unrecognized, may present with cardiovascular collapse, making it a potentially life-threatening entity. CASE PRESENTATION: The proposita, 11 months old of age, was admitted for lethargy and severe dehydration. Blood pressure was 62/38 mm Hg, and biochemical measurements showed hyponatraemia, hypochloraemia, hyperkalaemia, and metabolic acidaemia. Renin activity was 1484 μU/mL; cortisol, 1.03 μg/dL (normal, 5-25 μg/dL); and corticotropin (ACTH), 4832 ng/L (normal, 9-52 ng/L). Adrenal deficiency was diagnosed, and replacement therapy with glucocorticoids and mineralocorticoids was initiated. After 40 days, ACTH was 797 ng/L. During follow-up, the patient started taking macrogol twice daily for constipation and experienced a significant increase in ACTH (3262 ng/L), which dropped to 648 ng/L when macrogol was stopped. After arbitrary reintroduction of macrogol, the child presented with hypoglycaemia, lethargy, weakness, and hypotonia; ACTH was 3145 ng/L. After again stopping macrogol, her ACTH was near normalized (323 ng/L). CONCLUSION: Hydrocortisone malabsorption may be caused by macrogol use. Because chronic constipation is frequently reported in children, the possibility that macrogol contributes to adrenal crisis should be taken in account