luca crescentini - Academia.edu (original) (raw)
Papers by luca crescentini
Remote Sensing
Accurate knowledge of snow cover extent, depth (SD), and water equivalent is essential for studyi... more Accurate knowledge of snow cover extent, depth (SD), and water equivalent is essential for studying the global water cycle, climate, and energy–mass exchange in the Earth–atmosphere system, as well as for water resources management. Ratio between SAR cross- and co-polarization backscattering (σVH/σVV) was used to monitor SD during snowy months in mountain areas; however, published results refer to short periods and show lack of correlation during non-snowy months. We analyze Sentinel-1A images from a study area in Central Pyrenees to generate and investigate (i) time series of σVH/σVV spatial dispersion, (ii) spatial distribution of pixelwise σVH/σVV temporal standard deviation, and (iii) fundamental modes of σVH/σVV evolution by non-negative matrix factorization. The spatial dispersion evolution and the first mode are highly correlated (correlation coefficients larger than 0.9) to SD evolution during the whole seven-year-long period, including snowy and non-snowy months. The local ...
Volcanic risk in the explosive Campi Flegrei (CF) caldera is extremely high, because of its locat... more Volcanic risk in the explosive Campi Flegrei (CF) caldera is extremely high, because of its location in a densely populated area about 15 km west of Naples inside the Campanian Plain. The caldera has been generally subsiding (at about 1.5 cm/yr) from 1538 (last eruption) till 1969. A substantial ground uplift, more than 1.5 m, occurred in the period 1969-1972 and, after a small subsidence of about 30 cm after 1972, a very large uplift occurred in the period 1982-1984 (about 1.8 m), with subsequent partial recovery (about 60 cm in 2 yr). Superposed on the still continuing subsidence are some short uplift phases (mini-uplifts with a few cm amplitude); ground level still remains about 2.5 m above pre-1970 levels at the town of Pozzuoli.
To investigate the effect of the Free Core Resonance (FCR) we use the data from two European stra... more To investigate the effect of the Free Core Resonance (FCR) we use the data from two European strain stations: Baksan (Russia), and Gran Sasso (Italy). Eight years of strain recorded by two crossed 90-m long laser interferometers (BA and BC) at Gran Sasso underground observatory, and six years of strain recorded by the 75-m long laser interferometer at Baksan underground observatory, have been analysed.
In March 2010 two borehole strainmeters and three Michelson tiltmeters within the Campi Flegrei v... more In March 2010 two borehole strainmeters and three Michelson tiltmeters within the Campi Flegrei volcanic system, Italy, registered an abrupt deformation signal that was followed 20 min later by seismic slip on a pair of onshore normal faults. We demonstrate that the observed strain changes were caused by a small but rapid volume decrease in a previously identified offshore ellipsoidal magma source or part of it. Although the total deflation was below the detectability of interferometric synthetic aperture radar and GPS, deflation observed rates were briefly 2 orders of magnitude more rapid than decadal inflation rates. We conclude that this high dilatational contraction rate was responsible for triggering seismicity and that this process may be responsible for the normal faulting often observed in the Campi Flegrei region. Our study quantifies the crucial role played by a transient, minor reduction in dilatational stress, in triggering slip on a fault near critical failure. Our subs...
Geophysical Research Letters, 2017
Physical Review B, 1998
Low-frequency Raman spectra of H2O and D2O single crystals at different temperatures have been me... more Low-frequency Raman spectra of H2O and D2O single crystals at different temperatures have been measured by using a DMDP2000 spectrometer. Thanks to the performances of the spectrometer, we have been able to measure spectra very close to the elastic line. Present data extend those already measured by Briganti et al. [Solid State Commun. 42, 493 (1982)] to a lower frequency
Optics Letters, 1992
By a new method of momentum-space excitation an increase of the spontaneous emission rate and a l... more By a new method of momentum-space excitation an increase of the spontaneous emission rate and a large reduction of the microlaser threshold are obtained. The method is demonstrated by an optically excited microlaser filled with europium atoms. The method is general and may be extended to active cavities with any dimension and geometry. Our results on spontaneous emission are interpreted as a demonstration of the firstorder interference of the vacuum field.
Geophysical Journal International, 2004
We study the effect of a superficial layer overlying a half-space on the surface displacements ca... more We study the effect of a superficial layer overlying a half-space on the surface displacements caused by uniform slipping of a dip-slip normal rectangular fault. We compute static coseismic displacements using a 3-D analytical code for different characteristics of the layered medium, different fault geometries and different configurations of bench marks to simulate different kinds of geodetic data (GPS, Synthetic Aperture Radar, and levellings). We perform both joint and separate inversions of the three components of synthetic displacement without constraining fault parameters, apart from strike and rake, and using a non-linear global inversion technique under the assumption of homogeneous half-space. Differences between synthetic displacements computed in the presence of the superficial soft layer and in a homogeneous half-space do not show a simple regular behaviour, even if a few features can be identified. Consequently, also retrieved parameters of the homogeneous equivalent fault obtained by unconstrained inversion of surface displacements do not show a simple regular behaviour. We point out that the presence of a superficial layer may lead to misestimating several fault parameters both using joint and separate inversions of the three components of synthetic displacement and that the effects of the presence of the superficial layer can change whether all fault parameters are left free in the inversions or not. In the inversion of any kind of coseismic geodetic data, fault size and slip can be largely misestimated, but the product (fault length) × (fault width) × slip, which is proportional to the seismic moment for a given rigidity modulus, is often well determined (within a few per cent). Because inversion of coseismic geodetic data assuming a layered medium is impracticable, we suggest that only a case-to-case study involving some kind of recursive determination of fault parameters through data correction seems to give the proper approach when layering is important.
Geophysical Journal International, 2008
Strain data recorded by two crossed laser extensometers operating in the Gran Sasso underground o... more Strain data recorded by two crossed laser extensometers operating in the Gran Sasso underground observatory recorded seismic free oscillations excited by the 2004 December 26 Sumatra-Andaman earthquake. The main source of instrumental noise can be mitigated by differencing data from the crossed strainmeter arms, so that the resulting differential strain data set offers an unprecedented resolution of the seismic toroidal free oscillations with periods T > 1000 s. We reconstruct the time evolution of selected free-oscillations for comparison with synthetic seismograms that include normal-mode coupling effects from Coriolis force, attenuation and ellipticity. Envelopes estimated for the Gran Sasso differential data set for free oscillations with period T < 1000 s (frequencies f > 1 mHz) are approximated adequately by a composite Centroid-Moment-Tensor (CMT) source with five subevents and an aggregate M w = 9.3 moment-magnitude. Envelopes for several toroidal free oscillations with T > 1000 s are predicted less well. The amplitude of the rarely observed mode 0 T 2 is overpredicted at Gran Sasso by roughly a factor of two, and other modes are underpredicted. The amplitude discrepancy for 0 T 2 is confirmed at selected exceptionally low-noise seismic stations. Hypothetical explanations include a slow-slip component of the seismic moment release, errors in the composite-CMT source model, unmodelled coupling effects to Earth's secular modes and feedback from the Sumatra-Andaman tsunami on Indian Ocean coastlines. Of these hypotheses, either an extended-duration strain release or tsunami feedback seem most plausible. The viability of the tsunami-feedback mechansim deserves further investigation.
Geophysical Journal International, 2012
We analyse eight years of discontinuous strain records from two crossed 90-m long laser interfero... more We analyse eight years of discontinuous strain records from two crossed 90-m long laser interferometers (extensometers) operating in the Gran Sasso underground observatory (Central Italy) to investigate the FCN parameters. At first, inverting realistic synthetic tidal parameters (amplitude and phase of eight diurnal tidal components) we show that the resolving power of strain tides is comparable to that of gravity tides if tidal parameters are inverted minimizing the L 2 misfit (as usually done). Both resolving powers improve if data are inverted minimizing the L 1 misfit, and this improvement is particularly notable for gravity tides. The analyses of strain records have been performed after correcting measured strain for local distortion of the regional strain field and ocean loading. Data are inverted minimizing the L 1 misfit. Parameter uncertainty assessment is performed both inverting synthetic tidal parameter sets, obtained from the real one by adding a random noise, and estimating the Bayesian marginal probabilities from an ensemble of parameter space samples. Even if we analyse data from a single station, our results for the period of the Free Core Nutation (about 429 sidereal days) are robust and comparable to those from gravity tides, obtained from the joint inversion of data from several stations. The quality factor is not well constrained because of the large uncertainty on the 1 phase; however our results are consistent with recently published values (≈20 000). The agreement between observations and predictions looks better than in any previous work that makes use of strain tides. Our inversions provide also an independent estimate of Re(h 1 − 3l 1), which is the dominating term in the resonance strength expression, in agreement with IERS Conventions (2003).
Geophysical Journal International, 2004
Several phenomena have been proposed as diagnostic precursors of earthquakes, including strain-ra... more Several phenomena have been proposed as diagnostic precursors of earthquakes, including strain-rate changes, changes in seismic wave velocities, electromagnetic signals, changes in groundwater levels and flow, radon anomalies, and acoustic emissions. Moreover, laboratory studies and models suggest that fault failure is preceded by subsonic pre-seismic slip. Most, if not all, those phenomena should produce an associated strain field detectable by close strain meters. Till now, most observations of crustal strain have not detected any pre-seismic deformation, thus constraining the size and strength of the pre-seismic phenomenon source. The constraint strictness depends on the time interval considered and on the distance of the strain meter from the source.
The 1908 Messina earthquake is one of the strongest historical seismic events that ever occurred ... more The 1908 Messina earthquake is one of the strongest historical seismic events that ever occurred in Italy, with more than 60,000 casualties and extensive damage. It was felt by people in a radius of ∼300 km, with maximum damage (XII degree Mercalli intensity scale) occurring in the cities of Messina and Reggio Calabria. This earthquake occurred ∼3 years after another large event in the area, located at sea, and was followed by a tsunami with sea waves as high as 12 m, entering locally up to 200 m inland (Platania, 1909). Smaller earthquakes were felt in the Messina region from 1 month before the main event to ∼10 years after. The 1908 earthquake was also accompanied by visible ground cracks (Baratta, 1910): the coastline road close to Messina showed a graben-type collapse, with fractures up to 100 m long and slip around 0.6 m. It is not clear if these fractures are related to the seismogenic fault or are landslides, and there is no clear evidence of further surface breaking. Precision double-run levelings were carried out a few years before the 1908 earthquake, and some lines were resurveyed just after the seismic event. Measurements were performed in 1898-1899 in Sicily, in 1907-1908 in Calabria, and in March 1909 both in Sicily and in Calabria. Data from leveling surveys have been used in the past to constrain source fault parameters. A non-linear unconstrained joint inversion of levelling data and first-motion polarities was firstly performed by Amoruso et al. (2002) and refined by Amoruso et al. (2006). All past studies have been carried out under the assumption of faulting in a homogeneous elastic half-space. Despite the large number of published models, the seismic source for the 1908 Messina earthquake is still controversial, mainly because of the difficulty in explaining the tsunami features. Here we show the results of the first (to our best knowledge) non-linear unconstrained inversion of levelling data under the assumption of faulting in a layered elastic half-space. The layered crustal model has been obtained from the 3D velocity model in Barberi et al. (2004). As in Amoruso et al. (2002) we model the earthquake using a single planar fault: slip is at first assumed to be uniform across the whole fault, then independent in a small set of coplanar subfaults, and finally smoothly variable across the fault. Differently from Amoruso et al. (2002), also the third step is accomplished using a global minimization technique.
Remote Sensing
Accurate knowledge of snow cover extent, depth (SD), and water equivalent is essential for studyi... more Accurate knowledge of snow cover extent, depth (SD), and water equivalent is essential for studying the global water cycle, climate, and energy–mass exchange in the Earth–atmosphere system, as well as for water resources management. Ratio between SAR cross- and co-polarization backscattering (σVH/σVV) was used to monitor SD during snowy months in mountain areas; however, published results refer to short periods and show lack of correlation during non-snowy months. We analyze Sentinel-1A images from a study area in Central Pyrenees to generate and investigate (i) time series of σVH/σVV spatial dispersion, (ii) spatial distribution of pixelwise σVH/σVV temporal standard deviation, and (iii) fundamental modes of σVH/σVV evolution by non-negative matrix factorization. The spatial dispersion evolution and the first mode are highly correlated (correlation coefficients larger than 0.9) to SD evolution during the whole seven-year-long period, including snowy and non-snowy months. The local ...
Volcanic risk in the explosive Campi Flegrei (CF) caldera is extremely high, because of its locat... more Volcanic risk in the explosive Campi Flegrei (CF) caldera is extremely high, because of its location in a densely populated area about 15 km west of Naples inside the Campanian Plain. The caldera has been generally subsiding (at about 1.5 cm/yr) from 1538 (last eruption) till 1969. A substantial ground uplift, more than 1.5 m, occurred in the period 1969-1972 and, after a small subsidence of about 30 cm after 1972, a very large uplift occurred in the period 1982-1984 (about 1.8 m), with subsequent partial recovery (about 60 cm in 2 yr). Superposed on the still continuing subsidence are some short uplift phases (mini-uplifts with a few cm amplitude); ground level still remains about 2.5 m above pre-1970 levels at the town of Pozzuoli.
To investigate the effect of the Free Core Resonance (FCR) we use the data from two European stra... more To investigate the effect of the Free Core Resonance (FCR) we use the data from two European strain stations: Baksan (Russia), and Gran Sasso (Italy). Eight years of strain recorded by two crossed 90-m long laser interferometers (BA and BC) at Gran Sasso underground observatory, and six years of strain recorded by the 75-m long laser interferometer at Baksan underground observatory, have been analysed.
In March 2010 two borehole strainmeters and three Michelson tiltmeters within the Campi Flegrei v... more In March 2010 two borehole strainmeters and three Michelson tiltmeters within the Campi Flegrei volcanic system, Italy, registered an abrupt deformation signal that was followed 20 min later by seismic slip on a pair of onshore normal faults. We demonstrate that the observed strain changes were caused by a small but rapid volume decrease in a previously identified offshore ellipsoidal magma source or part of it. Although the total deflation was below the detectability of interferometric synthetic aperture radar and GPS, deflation observed rates were briefly 2 orders of magnitude more rapid than decadal inflation rates. We conclude that this high dilatational contraction rate was responsible for triggering seismicity and that this process may be responsible for the normal faulting often observed in the Campi Flegrei region. Our study quantifies the crucial role played by a transient, minor reduction in dilatational stress, in triggering slip on a fault near critical failure. Our subs...
Geophysical Research Letters, 2017
Physical Review B, 1998
Low-frequency Raman spectra of H2O and D2O single crystals at different temperatures have been me... more Low-frequency Raman spectra of H2O and D2O single crystals at different temperatures have been measured by using a DMDP2000 spectrometer. Thanks to the performances of the spectrometer, we have been able to measure spectra very close to the elastic line. Present data extend those already measured by Briganti et al. [Solid State Commun. 42, 493 (1982)] to a lower frequency
Optics Letters, 1992
By a new method of momentum-space excitation an increase of the spontaneous emission rate and a l... more By a new method of momentum-space excitation an increase of the spontaneous emission rate and a large reduction of the microlaser threshold are obtained. The method is demonstrated by an optically excited microlaser filled with europium atoms. The method is general and may be extended to active cavities with any dimension and geometry. Our results on spontaneous emission are interpreted as a demonstration of the firstorder interference of the vacuum field.
Geophysical Journal International, 2004
We study the effect of a superficial layer overlying a half-space on the surface displacements ca... more We study the effect of a superficial layer overlying a half-space on the surface displacements caused by uniform slipping of a dip-slip normal rectangular fault. We compute static coseismic displacements using a 3-D analytical code for different characteristics of the layered medium, different fault geometries and different configurations of bench marks to simulate different kinds of geodetic data (GPS, Synthetic Aperture Radar, and levellings). We perform both joint and separate inversions of the three components of synthetic displacement without constraining fault parameters, apart from strike and rake, and using a non-linear global inversion technique under the assumption of homogeneous half-space. Differences between synthetic displacements computed in the presence of the superficial soft layer and in a homogeneous half-space do not show a simple regular behaviour, even if a few features can be identified. Consequently, also retrieved parameters of the homogeneous equivalent fault obtained by unconstrained inversion of surface displacements do not show a simple regular behaviour. We point out that the presence of a superficial layer may lead to misestimating several fault parameters both using joint and separate inversions of the three components of synthetic displacement and that the effects of the presence of the superficial layer can change whether all fault parameters are left free in the inversions or not. In the inversion of any kind of coseismic geodetic data, fault size and slip can be largely misestimated, but the product (fault length) × (fault width) × slip, which is proportional to the seismic moment for a given rigidity modulus, is often well determined (within a few per cent). Because inversion of coseismic geodetic data assuming a layered medium is impracticable, we suggest that only a case-to-case study involving some kind of recursive determination of fault parameters through data correction seems to give the proper approach when layering is important.
Geophysical Journal International, 2008
Strain data recorded by two crossed laser extensometers operating in the Gran Sasso underground o... more Strain data recorded by two crossed laser extensometers operating in the Gran Sasso underground observatory recorded seismic free oscillations excited by the 2004 December 26 Sumatra-Andaman earthquake. The main source of instrumental noise can be mitigated by differencing data from the crossed strainmeter arms, so that the resulting differential strain data set offers an unprecedented resolution of the seismic toroidal free oscillations with periods T > 1000 s. We reconstruct the time evolution of selected free-oscillations for comparison with synthetic seismograms that include normal-mode coupling effects from Coriolis force, attenuation and ellipticity. Envelopes estimated for the Gran Sasso differential data set for free oscillations with period T < 1000 s (frequencies f > 1 mHz) are approximated adequately by a composite Centroid-Moment-Tensor (CMT) source with five subevents and an aggregate M w = 9.3 moment-magnitude. Envelopes for several toroidal free oscillations with T > 1000 s are predicted less well. The amplitude of the rarely observed mode 0 T 2 is overpredicted at Gran Sasso by roughly a factor of two, and other modes are underpredicted. The amplitude discrepancy for 0 T 2 is confirmed at selected exceptionally low-noise seismic stations. Hypothetical explanations include a slow-slip component of the seismic moment release, errors in the composite-CMT source model, unmodelled coupling effects to Earth's secular modes and feedback from the Sumatra-Andaman tsunami on Indian Ocean coastlines. Of these hypotheses, either an extended-duration strain release or tsunami feedback seem most plausible. The viability of the tsunami-feedback mechansim deserves further investigation.
Geophysical Journal International, 2012
We analyse eight years of discontinuous strain records from two crossed 90-m long laser interfero... more We analyse eight years of discontinuous strain records from two crossed 90-m long laser interferometers (extensometers) operating in the Gran Sasso underground observatory (Central Italy) to investigate the FCN parameters. At first, inverting realistic synthetic tidal parameters (amplitude and phase of eight diurnal tidal components) we show that the resolving power of strain tides is comparable to that of gravity tides if tidal parameters are inverted minimizing the L 2 misfit (as usually done). Both resolving powers improve if data are inverted minimizing the L 1 misfit, and this improvement is particularly notable for gravity tides. The analyses of strain records have been performed after correcting measured strain for local distortion of the regional strain field and ocean loading. Data are inverted minimizing the L 1 misfit. Parameter uncertainty assessment is performed both inverting synthetic tidal parameter sets, obtained from the real one by adding a random noise, and estimating the Bayesian marginal probabilities from an ensemble of parameter space samples. Even if we analyse data from a single station, our results for the period of the Free Core Nutation (about 429 sidereal days) are robust and comparable to those from gravity tides, obtained from the joint inversion of data from several stations. The quality factor is not well constrained because of the large uncertainty on the 1 phase; however our results are consistent with recently published values (≈20 000). The agreement between observations and predictions looks better than in any previous work that makes use of strain tides. Our inversions provide also an independent estimate of Re(h 1 − 3l 1), which is the dominating term in the resonance strength expression, in agreement with IERS Conventions (2003).
Geophysical Journal International, 2004
Several phenomena have been proposed as diagnostic precursors of earthquakes, including strain-ra... more Several phenomena have been proposed as diagnostic precursors of earthquakes, including strain-rate changes, changes in seismic wave velocities, electromagnetic signals, changes in groundwater levels and flow, radon anomalies, and acoustic emissions. Moreover, laboratory studies and models suggest that fault failure is preceded by subsonic pre-seismic slip. Most, if not all, those phenomena should produce an associated strain field detectable by close strain meters. Till now, most observations of crustal strain have not detected any pre-seismic deformation, thus constraining the size and strength of the pre-seismic phenomenon source. The constraint strictness depends on the time interval considered and on the distance of the strain meter from the source.
The 1908 Messina earthquake is one of the strongest historical seismic events that ever occurred ... more The 1908 Messina earthquake is one of the strongest historical seismic events that ever occurred in Italy, with more than 60,000 casualties and extensive damage. It was felt by people in a radius of ∼300 km, with maximum damage (XII degree Mercalli intensity scale) occurring in the cities of Messina and Reggio Calabria. This earthquake occurred ∼3 years after another large event in the area, located at sea, and was followed by a tsunami with sea waves as high as 12 m, entering locally up to 200 m inland (Platania, 1909). Smaller earthquakes were felt in the Messina region from 1 month before the main event to ∼10 years after. The 1908 earthquake was also accompanied by visible ground cracks (Baratta, 1910): the coastline road close to Messina showed a graben-type collapse, with fractures up to 100 m long and slip around 0.6 m. It is not clear if these fractures are related to the seismogenic fault or are landslides, and there is no clear evidence of further surface breaking. Precision double-run levelings were carried out a few years before the 1908 earthquake, and some lines were resurveyed just after the seismic event. Measurements were performed in 1898-1899 in Sicily, in 1907-1908 in Calabria, and in March 1909 both in Sicily and in Calabria. Data from leveling surveys have been used in the past to constrain source fault parameters. A non-linear unconstrained joint inversion of levelling data and first-motion polarities was firstly performed by Amoruso et al. (2002) and refined by Amoruso et al. (2006). All past studies have been carried out under the assumption of faulting in a homogeneous elastic half-space. Despite the large number of published models, the seismic source for the 1908 Messina earthquake is still controversial, mainly because of the difficulty in explaining the tsunami features. Here we show the results of the first (to our best knowledge) non-linear unconstrained inversion of levelling data under the assumption of faulting in a layered elastic half-space. The layered crustal model has been obtained from the 3D velocity model in Barberi et al. (2004). As in Amoruso et al. (2002) we model the earthquake using a single planar fault: slip is at first assumed to be uniform across the whole fault, then independent in a small set of coplanar subfaults, and finally smoothly variable across the fault. Differently from Amoruso et al. (2002), also the third step is accomplished using a global minimization technique.