Continuous gravity observations performed in the last few years, both at Mt. Etna and Stromboli, ... more Continuous gravity observations performed in the last few years, both at Mt. Etna and Stromboli, have prompted the need to improve the tidal analysis in order to acquire the best corrected data for the detection of volcano related signals. On Mt. Etna, the sites are very close to each other and the expected tidal factor differences are negligible. It is thus useful to unify the tidal analysis results of the different data sets in a unique tidal model. This tidal model, which can be independently confirmed by a modeling of the tidal parameters based on the elastic response of the Earth to tidal forces and the computation of the ocean tides effects on gravity, is very useful for the precise tidal gravity prediction required by absolute or relative discrete gravity measurements. The change in time of the gravimeters' sensitivity is also an important issue to be checked since it affects not only the results of tidal analysis but also the accuracy of the observed gravity changes. Conversely, if a good tidal model is available, the sensitivity variations can be accurately reconstructed so as to retune observed tidal records with the synthetic tide, since the tidal parameters are assumed to be constant at a given location.
Assessment of the ongoing activity of volcanoes is one of the key factors to reduce volcanic risk... more Assessment of the ongoing activity of volcanoes is one of the key factors to reduce volcanic risks. In this paper, two Machine Learning (ML) approaches are presented to classify volcanic activity using multivariate geophysical data, namely the Decision Tree (DT) and K-Nearest Neighbours (KNN). The models were implemented using a data set recorded at Mount Etna (Italy), in the period 01 January 2011 -31 December 2015, encompassing lava fountain events and intense Strombolian activity. Here a data set consisting of five geophysical features, namely the root-mean-square of seismic tremor (RMS) and its source depth, counts of clustered infrasonic events, radar RMS backscattering power and tilt derivative, was considered. Model performances were assessed by using a set of statistical indices commonly considered for classification approaches. Results show that between the investigated approaches the DT model is the most appropriate for classification of volcano activity and is suitable for early warning systems applications. Furthermore, the comparison with a different classifier approach, reported in literature, based on Bayesian Network (BN), is performed.
ABSTRACT Geophysical (tilt, seismic tremor and gravity signals), geochemical (crater SO2 flux) an... more ABSTRACT Geophysical (tilt, seismic tremor and gravity signals), geochemical (crater SO2 flux) and infrared satellite measurements are presented and discussed to track the temporal evolution of the lava fountain episode occurring at Mt Etna volcano on 10 April 2011. The multi-disciplinary approach provides insight into a gas-rich magma source trapped in a shallow storage zone inside the volcano edifice. This generated the fast ascending gas-magma dispersed flow feeding the lava fountain and causing the depressurization of a deeper magma storage. Satellite thermal data allowed estimation of the amount of erupted lava, which, summed to the tephra volume, yielded a total volume of erupted products of about 1 × 106 m3. Thanks to the daylight occurrence of this eruptive episode, the SO2 emission rate was also estimated, showing a degassing cycle reaching a peak of 15,000 Mg d-1 with a mean daily value of ˜5,700 Mg d-1. The SO2 data from the previous fountain episode on 17-18 February to 10 April 2011, yielded a cumulative degassed magma volume of about ˜10.5 × 106 m3, indicating a ratio of roughly 10:1 between degassed and erupted volumes. This volumetric balance, differently from those previously estimated during different styles of volcanic activities with long-term (years) recharging periods and middle-term (weeks to months) effusive eruptions, points toward the predominant role played by the gas phase in generating and driving this lava fountain episode.
Egu General Assembly Conference Abstracts, May 1, 2010
... Island (Italy) 2 3 Rosalba Napoli 1 , Gilda Currenti 1 , Ciro Del Negro 1 , Agnese Di Stefano... more ... Island (Italy) 2 3 Rosalba Napoli 1 , Gilda Currenti 1 , Ciro Del Negro 1 , Agnese Di Stefano 1,2 , Filippo Greco 1 and 4 ... 100 All stations were devised using robust technologic components, which guarantee 101 uninterrupted working under harsh environmental conditions. ...
Employing both absolute and relative gravimeters, we carried out three hybrid microgravity survey... more Employing both absolute and relative gravimeters, we carried out three hybrid microgravity surveys at Etna volcano between 2007 and 2009. The repeated measurements highlighted the spatio-time evolution of the gravity field associated with the volcanic unrest. We detected a gravity increase attained an amplitude of about 80 µGal on the summit area of the volcano between July 2008 and July 2009. The observed gravity increase could reflect mass accumulations into shallow magma storage system of the volcano located at 1÷2 km below sea level. We present here data and the advantages in using the combined approach of relative and absolute measurements performed at Etna volcano.
This paper reports the results from the accurate measurement of the acceleration of gravity g tak... more This paper reports the results from the accurate measurement of the acceleration of gravity g taken at two separate premises in the Polo Scientifico of the University of Firenze (Italy). In these laboratories, two separate experiments aiming at measuring the Newtonian constant and testing the Newtonian law at short distances are in progress. Both experiments require an independent knowledge on the local value of g. The only available datum, pertaining to the italian zero-order gravity network, was taken more than 20 years ago at a distance of more than 60 km from the study site. Gravity measurements were conducted using an FG5 absolute gravimeter, and accompanied by seismic recordings for evaluating the noise condition at the site. The absolute accelerations of gravity at the two laboratories are (980 492 160.6 ± 4.0) µGal and (980 492 048.3 ± 3.0) µGal for the European Laboratory for Non-Linear Spectroscopy (LENS) and Dipartimento di Fisica e Astronomia, respectively. Other than for the two referenced experiments, the data here presented will serve as a benchmark for any future study requiring an accurate knowledge of the absolute value of the acceleration of gravity in the study region.
This study summarizes the results obtained by using a processing method based on wavelet transfor... more This study summarizes the results obtained by using a processing method based on wavelet transform for noise-filtering of continuous gravity data. Continuous gravity recordings in volcanic area could play a fundamental role in the monitoring of active volcanoes and in the prediction of eruptive events too. This geophysical methodology is used, on active volcanoes, in order to detect mass changes linked to magma transfer processes and, thus, to recognize forerunners to paroxysmal volcanic events. Spring gravimeters are still the most utilized instruments for this type of microgravity studies. Unfortunately, spring gravity meters show a strong influence of meteorological parameters, especially in the adverse environmental conditions usually encountered at such places. As the gravity changes due to the volcanic activity are very small compared to other geophysical or instrumental effects, we need a new mathematical tool to get reliable gravity residuals susceptible to reflect the volcanic effect. The aim of the present work is to get a first evaluation about the comparison between the traditional filtering methodology and the wavelet transform. The overall results show that the performance of the wavelet-based filter seems better than the Fourier one. Moreover, the possibility of getting a multi-resolution analysis and study local features of the signal in the time domain makes the proposed methodology a valuable tool for gravity data processing.
Il valore di X H2O m , inoltre, è stato ottenuto tramite esperimenti condotti con apparecchiature... more Il valore di X H2O m , inoltre, è stato ottenuto tramite esperimenti condotti con apparecchiature EHPV tipo TZM a quenching ultrarapido. Da questi esperimenti, effettuati alle temperature e pressioni di interesse e per X H2O m compreso fra 0 ed il livello di saturazione, è stato possibile costruire una retta di calibrazione nella quale la composizione del plagioclasio in equilibrio con il fuso [X(An) Plag ] risulta funzione del quantitativo di H 2 O disciolta nel fuso stesso. In questo modo sono stati ricavati i contenuti d'acqua dei magmi riolitico e trachitico, stimati rispettivamente a 2,4-2,9% e 1,7-2,7%. Questi dati suggeriscono infine come l'evoluzione magmatica del sistema di alimentazione del Vulcano La Fossa, possa essere spiegata sulla base della differenziazione da termini latitici e trachitici delle eruzioni iniziali (Punte Nere e Grotte dei Palizzi) a quelli riolitici delle eruzioni più recenti (Pietre Cotte, 1888-90), nei quali è tuttavia preservata la testimonianza dei magmi primitivi.
ABSTRACT 18-years (September 1994 - October 2011) gravity and ground deformation sequences, recor... more ABSTRACT 18-years (September 1994 - October 2011) gravity and ground deformation sequences, recorded at Etna volcano along an East-West trending profile of 19 stations on the southern flank at a quasi-monthly sampling rate, are presented. Over the last two decades, frequent fountaining events and several flank eruptions occurred at Mt Etna. We use the SBAS DInSAR technique to analyze the temporal evolution of surface displacements by inverting a sequence of interferograms to form a deformation time series. Height changes, evaluated by DInSAR data during the entire period, show modest vertical variations unable to produce significant gravity changes. However, the gravity data set was corrected for the small height variations using the experimental free-air gravity gradients measured at two stations of the profile. The residual space-time gravity image displayed some gravity increase/decrease cycles, mostly affecting the central and eastern stations of the East-West profile. We attributed these gravity cycles to mass redistribution processes mainly located at a depth of 2-4 km bsl in a region recognized to be a preferential pathway of magma rising and an intermediate zone of magma storage/withdrawal. In the latter period 2008-2011, when several paroxysmal events occurred from the South East crater, the gravity and height deformation patterns show many similarities with the previous period 1995-2000 encompassing a long series of paroxysmal episodes that preceded the violent and dramatic explosive/effusive eruptions of 2001 and 2002-2003.
Microgravity observations at Mt. Etna have been routinely performed as both discrete (since 1986)... more Microgravity observations at Mt. Etna have been routinely performed as both discrete (since 1986) and continuous (since 1998) measurements. In addition to describing the methodology for acquiring and reducing gravity data from Mt. Etna, this paper provides a collection of case studies aimed at demonstrating the potential of microgravity to investigate the plumbing system of an active volcano and detect forerunners to paroxysmal volcanic events. For discrete gravity measurements, results from 1994-1996 and 2001 are reported. During the first period, the observed gravity changes are interpreted within the framework of the Strombolian activity which occurred from the summit craters. Gravity changes observed during the first nine months of 2001 are directly related to subsurface mass redistributions which preceded, accompanied and followed the July-August 2001 flank eruption of Mt. Etna. Two continuous gravity records are discussed: a 16-month (October 1998 to February 2000) sequence and a 48-hour (26-28 October, 2002) sequence, both from a station within a few kilometers of the volcano's summit. The 16-month record may be the longest continuous gravity sequence ever acquired at a station very close to the summit zone of an active volcano. By cross analyzing it with contemporaneous discrete observations along a summit profile of stations, both the geometry of a buried source and its time evolution can be investigated. The shorter continuous sequence encompasses the onset of an eruption from a location only 1.5 km from the gravity station. This gravity record is useful for establishing constraints on the characteristics of the intrusive mechanism leading to the eruption. In particular, the observed gravity anomaly indicates that the magma intrusion occurred ''passively'' within a fracture system opened by external forces.
where Qi − 1 and Qr − 1 represent the energy losses due to intrinsic attenuation and radiation, r... more where Qi − 1 and Qr − 1 represent the energy losses due to intrinsic attenuation and radiation, respectively.
Continuous gravity observations performed in the last few years, both at Mt. Etna and Stromboli, ... more Continuous gravity observations performed in the last few years, both at Mt. Etna and Stromboli, have prompted the need to improve the tidal analysis in order to acquire the best corrected data for the detection of volcano related signals. On Mt. Etna, the sites are very ...
Accurate detection of time gravity changes attributable to the dynamics of volcanoes requires hig... more Accurate detection of time gravity changes attributable to the dynamics of volcanoes requires high-precision gravity measurements. With the aim of improving the quality of data from the Mount Etna gravity network, we used both absolute and relative gravimeters in a hybrid method. In this report, some of the techniques for gravity surveys are reviewed, and the results related to each method are compared. We show how the total uncertainty estimated for the gravity measurements performed with this combined use of absolute and relative gravimeters is roughly comparable to that calculated when the measurements are acquired using only relative gravimeters (the traditional method). However, the data highlight how the hybrid approach improves the measurement capabilities for surveying the Mount Etna volcanic area. This approach enhances the accuracy of the data, and then of the four-dimensional surveying, which minimizes ambiguities inherent in the gravity measurements. As a case study, we refer to two gravity datasets acquired in 2005 and 2010 from the western part of the Etna volcano, which included five absolute and 13 relative stations of the Etna gravity network. 2. Gravity network surveying Mt. Etna volcano The Mt. Etna gravity network was set up in 1986, and to reach its present configuration, it has been under continuous development over the intervening years. It consists of 71 Article history
ABSTRACT We present a multidisciplinary set of recent and new data that allowed to make a step fo... more ABSTRACT We present a multidisciplinary set of recent and new data that allowed to make a step forward in studying the internal mechanisms of a powerful lava fountain occurred at Etna volcano. In particular, the negative change in the signals recorded at two borehole strainmeters, installed just two weeks before the explosive event, gives clear evidence of a deep depressurizing source (depth of ca. 6-8 km below summit craters). The decompression was well recorded at both the two stations located at a radial distance from summit craters of 6 and 10 km, respectively. Due to the exceptional accuracy of the strainmeters (the nominal resolution is of about 10E-12 in strain), this episode represents the first time that strain field changes are observed at Etna with such precision during a lava fountain. As for other previous episodes, during the lava fountain the gravity signals of the two continuous stations showed a different reversal trend that inferred a shallower (ca. 1.5 km below summit craters) source, where the low density rich-gas magma (foam) accumulated and then was released during the lava fountain. Therefore, this set of data (strain and gravity) allowed to infer the positions of two intermediate storages involved in the shallow-intermediate plumbing system. Also magnetic data recorded a significant permanent piezomagnetic variation of about 3 nT providing useful constraints on the stress field. The piezomagnetic effect depends directly on the deviatoric stress and, hence, gave insights into the internal overpressure within the volcano edifice. During this event, satellite data acquired by MSG-SEVIRI (3 km of spatial resolution, 15 minutes of sample time) were elaborated to detect thermal anomalies, to compute a radiant heat flux and to provide an estimation of the emitted volume. Both strain signals and SEVIRI-derived radiant heat flux started to show a first significant change few hours before the lava fountain beginning, when also a lava flow was emitted from SE crater anticipating the paroxysmal event. The estimate of the emitted volume allowed to infer the overpressure released during the explosive episode, thus also providing constraints on pressure change associated with the depressurizing sources.
Continuous gravity observations performed in the last few years, both at Mt. Etna and Stromboli, ... more Continuous gravity observations performed in the last few years, both at Mt. Etna and Stromboli, have prompted the need to improve the tidal analysis in order to acquire the best corrected data for the detection of volcano related signals. On Mt. Etna, the sites are very close to each other and the expected tidal factor differences are negligible. It is thus useful to unify the tidal analysis results of the different data sets in a unique tidal model. This tidal model, which can be independently confirmed by a modeling of the tidal parameters based on the elastic response of the Earth to tidal forces and the computation of the ocean tides effects on gravity, is very useful for the precise tidal gravity prediction required by absolute or relative discrete gravity measurements. The change in time of the gravimeters' sensitivity is also an important issue to be checked since it affects not only the results of tidal analysis but also the accuracy of the observed gravity changes. Conversely, if a good tidal model is available, the sensitivity variations can be accurately reconstructed so as to retune observed tidal records with the synthetic tide, since the tidal parameters are assumed to be constant at a given location.
Assessment of the ongoing activity of volcanoes is one of the key factors to reduce volcanic risk... more Assessment of the ongoing activity of volcanoes is one of the key factors to reduce volcanic risks. In this paper, two Machine Learning (ML) approaches are presented to classify volcanic activity using multivariate geophysical data, namely the Decision Tree (DT) and K-Nearest Neighbours (KNN). The models were implemented using a data set recorded at Mount Etna (Italy), in the period 01 January 2011 -31 December 2015, encompassing lava fountain events and intense Strombolian activity. Here a data set consisting of five geophysical features, namely the root-mean-square of seismic tremor (RMS) and its source depth, counts of clustered infrasonic events, radar RMS backscattering power and tilt derivative, was considered. Model performances were assessed by using a set of statistical indices commonly considered for classification approaches. Results show that between the investigated approaches the DT model is the most appropriate for classification of volcano activity and is suitable for early warning systems applications. Furthermore, the comparison with a different classifier approach, reported in literature, based on Bayesian Network (BN), is performed.
ABSTRACT Geophysical (tilt, seismic tremor and gravity signals), geochemical (crater SO2 flux) an... more ABSTRACT Geophysical (tilt, seismic tremor and gravity signals), geochemical (crater SO2 flux) and infrared satellite measurements are presented and discussed to track the temporal evolution of the lava fountain episode occurring at Mt Etna volcano on 10 April 2011. The multi-disciplinary approach provides insight into a gas-rich magma source trapped in a shallow storage zone inside the volcano edifice. This generated the fast ascending gas-magma dispersed flow feeding the lava fountain and causing the depressurization of a deeper magma storage. Satellite thermal data allowed estimation of the amount of erupted lava, which, summed to the tephra volume, yielded a total volume of erupted products of about 1 × 106 m3. Thanks to the daylight occurrence of this eruptive episode, the SO2 emission rate was also estimated, showing a degassing cycle reaching a peak of 15,000 Mg d-1 with a mean daily value of ˜5,700 Mg d-1. The SO2 data from the previous fountain episode on 17-18 February to 10 April 2011, yielded a cumulative degassed magma volume of about ˜10.5 × 106 m3, indicating a ratio of roughly 10:1 between degassed and erupted volumes. This volumetric balance, differently from those previously estimated during different styles of volcanic activities with long-term (years) recharging periods and middle-term (weeks to months) effusive eruptions, points toward the predominant role played by the gas phase in generating and driving this lava fountain episode.
Egu General Assembly Conference Abstracts, May 1, 2010
... Island (Italy) 2 3 Rosalba Napoli 1 , Gilda Currenti 1 , Ciro Del Negro 1 , Agnese Di Stefano... more ... Island (Italy) 2 3 Rosalba Napoli 1 , Gilda Currenti 1 , Ciro Del Negro 1 , Agnese Di Stefano 1,2 , Filippo Greco 1 and 4 ... 100 All stations were devised using robust technologic components, which guarantee 101 uninterrupted working under harsh environmental conditions. ...
Employing both absolute and relative gravimeters, we carried out three hybrid microgravity survey... more Employing both absolute and relative gravimeters, we carried out three hybrid microgravity surveys at Etna volcano between 2007 and 2009. The repeated measurements highlighted the spatio-time evolution of the gravity field associated with the volcanic unrest. We detected a gravity increase attained an amplitude of about 80 µGal on the summit area of the volcano between July 2008 and July 2009. The observed gravity increase could reflect mass accumulations into shallow magma storage system of the volcano located at 1÷2 km below sea level. We present here data and the advantages in using the combined approach of relative and absolute measurements performed at Etna volcano.
This paper reports the results from the accurate measurement of the acceleration of gravity g tak... more This paper reports the results from the accurate measurement of the acceleration of gravity g taken at two separate premises in the Polo Scientifico of the University of Firenze (Italy). In these laboratories, two separate experiments aiming at measuring the Newtonian constant and testing the Newtonian law at short distances are in progress. Both experiments require an independent knowledge on the local value of g. The only available datum, pertaining to the italian zero-order gravity network, was taken more than 20 years ago at a distance of more than 60 km from the study site. Gravity measurements were conducted using an FG5 absolute gravimeter, and accompanied by seismic recordings for evaluating the noise condition at the site. The absolute accelerations of gravity at the two laboratories are (980 492 160.6 ± 4.0) µGal and (980 492 048.3 ± 3.0) µGal for the European Laboratory for Non-Linear Spectroscopy (LENS) and Dipartimento di Fisica e Astronomia, respectively. Other than for the two referenced experiments, the data here presented will serve as a benchmark for any future study requiring an accurate knowledge of the absolute value of the acceleration of gravity in the study region.
This study summarizes the results obtained by using a processing method based on wavelet transfor... more This study summarizes the results obtained by using a processing method based on wavelet transform for noise-filtering of continuous gravity data. Continuous gravity recordings in volcanic area could play a fundamental role in the monitoring of active volcanoes and in the prediction of eruptive events too. This geophysical methodology is used, on active volcanoes, in order to detect mass changes linked to magma transfer processes and, thus, to recognize forerunners to paroxysmal volcanic events. Spring gravimeters are still the most utilized instruments for this type of microgravity studies. Unfortunately, spring gravity meters show a strong influence of meteorological parameters, especially in the adverse environmental conditions usually encountered at such places. As the gravity changes due to the volcanic activity are very small compared to other geophysical or instrumental effects, we need a new mathematical tool to get reliable gravity residuals susceptible to reflect the volcanic effect. The aim of the present work is to get a first evaluation about the comparison between the traditional filtering methodology and the wavelet transform. The overall results show that the performance of the wavelet-based filter seems better than the Fourier one. Moreover, the possibility of getting a multi-resolution analysis and study local features of the signal in the time domain makes the proposed methodology a valuable tool for gravity data processing.
Il valore di X H2O m , inoltre, è stato ottenuto tramite esperimenti condotti con apparecchiature... more Il valore di X H2O m , inoltre, è stato ottenuto tramite esperimenti condotti con apparecchiature EHPV tipo TZM a quenching ultrarapido. Da questi esperimenti, effettuati alle temperature e pressioni di interesse e per X H2O m compreso fra 0 ed il livello di saturazione, è stato possibile costruire una retta di calibrazione nella quale la composizione del plagioclasio in equilibrio con il fuso [X(An) Plag ] risulta funzione del quantitativo di H 2 O disciolta nel fuso stesso. In questo modo sono stati ricavati i contenuti d'acqua dei magmi riolitico e trachitico, stimati rispettivamente a 2,4-2,9% e 1,7-2,7%. Questi dati suggeriscono infine come l'evoluzione magmatica del sistema di alimentazione del Vulcano La Fossa, possa essere spiegata sulla base della differenziazione da termini latitici e trachitici delle eruzioni iniziali (Punte Nere e Grotte dei Palizzi) a quelli riolitici delle eruzioni più recenti (Pietre Cotte, 1888-90), nei quali è tuttavia preservata la testimonianza dei magmi primitivi.
ABSTRACT 18-years (September 1994 - October 2011) gravity and ground deformation sequences, recor... more ABSTRACT 18-years (September 1994 - October 2011) gravity and ground deformation sequences, recorded at Etna volcano along an East-West trending profile of 19 stations on the southern flank at a quasi-monthly sampling rate, are presented. Over the last two decades, frequent fountaining events and several flank eruptions occurred at Mt Etna. We use the SBAS DInSAR technique to analyze the temporal evolution of surface displacements by inverting a sequence of interferograms to form a deformation time series. Height changes, evaluated by DInSAR data during the entire period, show modest vertical variations unable to produce significant gravity changes. However, the gravity data set was corrected for the small height variations using the experimental free-air gravity gradients measured at two stations of the profile. The residual space-time gravity image displayed some gravity increase/decrease cycles, mostly affecting the central and eastern stations of the East-West profile. We attributed these gravity cycles to mass redistribution processes mainly located at a depth of 2-4 km bsl in a region recognized to be a preferential pathway of magma rising and an intermediate zone of magma storage/withdrawal. In the latter period 2008-2011, when several paroxysmal events occurred from the South East crater, the gravity and height deformation patterns show many similarities with the previous period 1995-2000 encompassing a long series of paroxysmal episodes that preceded the violent and dramatic explosive/effusive eruptions of 2001 and 2002-2003.
Microgravity observations at Mt. Etna have been routinely performed as both discrete (since 1986)... more Microgravity observations at Mt. Etna have been routinely performed as both discrete (since 1986) and continuous (since 1998) measurements. In addition to describing the methodology for acquiring and reducing gravity data from Mt. Etna, this paper provides a collection of case studies aimed at demonstrating the potential of microgravity to investigate the plumbing system of an active volcano and detect forerunners to paroxysmal volcanic events. For discrete gravity measurements, results from 1994-1996 and 2001 are reported. During the first period, the observed gravity changes are interpreted within the framework of the Strombolian activity which occurred from the summit craters. Gravity changes observed during the first nine months of 2001 are directly related to subsurface mass redistributions which preceded, accompanied and followed the July-August 2001 flank eruption of Mt. Etna. Two continuous gravity records are discussed: a 16-month (October 1998 to February 2000) sequence and a 48-hour (26-28 October, 2002) sequence, both from a station within a few kilometers of the volcano's summit. The 16-month record may be the longest continuous gravity sequence ever acquired at a station very close to the summit zone of an active volcano. By cross analyzing it with contemporaneous discrete observations along a summit profile of stations, both the geometry of a buried source and its time evolution can be investigated. The shorter continuous sequence encompasses the onset of an eruption from a location only 1.5 km from the gravity station. This gravity record is useful for establishing constraints on the characteristics of the intrusive mechanism leading to the eruption. In particular, the observed gravity anomaly indicates that the magma intrusion occurred ''passively'' within a fracture system opened by external forces.
where Qi − 1 and Qr − 1 represent the energy losses due to intrinsic attenuation and radiation, r... more where Qi − 1 and Qr − 1 represent the energy losses due to intrinsic attenuation and radiation, respectively.
Continuous gravity observations performed in the last few years, both at Mt. Etna and Stromboli, ... more Continuous gravity observations performed in the last few years, both at Mt. Etna and Stromboli, have prompted the need to improve the tidal analysis in order to acquire the best corrected data for the detection of volcano related signals. On Mt. Etna, the sites are very ...
Accurate detection of time gravity changes attributable to the dynamics of volcanoes requires hig... more Accurate detection of time gravity changes attributable to the dynamics of volcanoes requires high-precision gravity measurements. With the aim of improving the quality of data from the Mount Etna gravity network, we used both absolute and relative gravimeters in a hybrid method. In this report, some of the techniques for gravity surveys are reviewed, and the results related to each method are compared. We show how the total uncertainty estimated for the gravity measurements performed with this combined use of absolute and relative gravimeters is roughly comparable to that calculated when the measurements are acquired using only relative gravimeters (the traditional method). However, the data highlight how the hybrid approach improves the measurement capabilities for surveying the Mount Etna volcanic area. This approach enhances the accuracy of the data, and then of the four-dimensional surveying, which minimizes ambiguities inherent in the gravity measurements. As a case study, we refer to two gravity datasets acquired in 2005 and 2010 from the western part of the Etna volcano, which included five absolute and 13 relative stations of the Etna gravity network. 2. Gravity network surveying Mt. Etna volcano The Mt. Etna gravity network was set up in 1986, and to reach its present configuration, it has been under continuous development over the intervening years. It consists of 71 Article history
ABSTRACT We present a multidisciplinary set of recent and new data that allowed to make a step fo... more ABSTRACT We present a multidisciplinary set of recent and new data that allowed to make a step forward in studying the internal mechanisms of a powerful lava fountain occurred at Etna volcano. In particular, the negative change in the signals recorded at two borehole strainmeters, installed just two weeks before the explosive event, gives clear evidence of a deep depressurizing source (depth of ca. 6-8 km below summit craters). The decompression was well recorded at both the two stations located at a radial distance from summit craters of 6 and 10 km, respectively. Due to the exceptional accuracy of the strainmeters (the nominal resolution is of about 10E-12 in strain), this episode represents the first time that strain field changes are observed at Etna with such precision during a lava fountain. As for other previous episodes, during the lava fountain the gravity signals of the two continuous stations showed a different reversal trend that inferred a shallower (ca. 1.5 km below summit craters) source, where the low density rich-gas magma (foam) accumulated and then was released during the lava fountain. Therefore, this set of data (strain and gravity) allowed to infer the positions of two intermediate storages involved in the shallow-intermediate plumbing system. Also magnetic data recorded a significant permanent piezomagnetic variation of about 3 nT providing useful constraints on the stress field. The piezomagnetic effect depends directly on the deviatoric stress and, hence, gave insights into the internal overpressure within the volcano edifice. During this event, satellite data acquired by MSG-SEVIRI (3 km of spatial resolution, 15 minutes of sample time) were elaborated to detect thermal anomalies, to compute a radiant heat flux and to provide an estimation of the emitted volume. Both strain signals and SEVIRI-derived radiant heat flux started to show a first significant change few hours before the lava fountain beginning, when also a lava flow was emitted from SE crater anticipating the paroxysmal event. The estimate of the emitted volume allowed to infer the overpressure released during the explosive episode, thus also providing constraints on pressure change associated with the depressurizing sources.
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Papers by F. Greco