40 research outputs found
Detailed analysis of wave propagation beneath the Campi Flegrei Caldera, Italy
We investigate the complex propagation of seismic waves beneath the
Campi Flegrei caldera, Italy, using multichannel recordings of
artificial explosions. The sources consisted of air gun explosions
shot in the Gulf of Pozzuoli at offsets ranging between 3 and 7 km. A
multichannel recording device was deployed in the Solfatara crater and
consisted of ten vertical-component and two three-component
short-period seismometers with a maximum aperture of about 150 m. The
zero-lag correlation (ZLC) technique was adopted to estimate
horizontal slowness and backazimuth of coherent waves crossing the
array. For sources located in the northern sector of the Gulf, with
maximum offset 5 km, ray parameters and backazimuths are in agreement
with those predicted for the 1D velocity model used for routine
locations. For sources at offsets larger than approximately 5 km, the
ZLC curves depict prominent maxima associated with a secondary phase
propagating with a lower velocity than the first-arrival P wave. Using
finite-difference synthetic seismograms generated for a 2D realistic
velocity model, we explain these late arrivals in terms of a lateral
velocity variation located at depths of about 1 km. Such discontinuity
would correspond to a positive V (sub p) anomaly imaged by a recent 3D
tomographic study, and interpreted as the submerged southern rim of
Campi Flegrei caldera collapsed during the explosive eruption of 12 ky
B.P. The small spacing among adjacent shot points allowed simultaneous
wave-field decomposition at the source and receiver arrays. Using a
modified version of the double-beam method, we retrieve the
independent variation of horizontal slowness at both the source and
receiver regions. For both cases, we found azimuthal deviations as
large as 50 degrees with respect to the great circle path. At the
source region, these discrepancies may be interpreted in terms of ray
bending at the interface of the aforementioned positive anomaly. At
the receiver array, the observed anomalies may be attributed to either
velocity variations marking the Solfatara crater rim, or to a
near-receiver, low-velocity body whose position would coincide with
negative gravimetric anomalies and a high V (sub p) /V (sub s) ratio
region inferred by independent geophysical and seismological studies
Complex wave propagation in the Campi Flegrei Caldera, Italy,from Source and receiver-array analysis of sea-shot recordings
We investigate wave propagation in the complex shallow crust of Campi Flegrei
Volcanic Complex, Italy, using array recordings of air-guns. We apply source- and
receiver-array analysis to define the independent variation of horizontal slowness at
both the source and receiver regions. This method allows the identification of
asymmetric ray-paths associated with near-source and near-observer velocity
heterogeneities. P-wave wave-vectors at both the source and receiver arrays depict
discrepancies as large as 50° with respect to the values expected for the 3D velocity
structure of the Gulf. At the source region, these discrepancies may be associated with
either un-modelled complexities in the geometry of the buried caldera rim, or with
velocity variations beneath the source-array. At the receiver array, the inferred
anomalies may be attributed to velocity variations marking the Solfatara crater rim, or
to a near-receiver, low-velocity body whose position would coincide with negative
gravimetric anomalies and a low Vp/Vs ratio region inferred by independent
geophysical and seismological studies
Detailed Analysis of Wave Propagation Beneath the Campi Flegrei Caldera (Italy)
We investigate the complex propagation of seismic waves beneath the Campi Flegrei Caldera, Italy, using
multichannel recordings of artificial explosions. The sources consisted of air gun explosions shot in the Gulf of
Pozzuoli at offsets ranging between 3 and 7 km. The multichannel recording device was deployed in the
Solfatara crater and consisted of 10 vertical-component and 2 three-component short-period seismometers with a
maximum aperture of about 150m. The Zero-Lag-Correlation (ZLC) technique was adopted to estimate
horizontal slowness and backazimuth of coherent waves crossing the array. For sources located in the northern
sector of the Gulf, with maximum offset 5 km, ray parameters and backazimuths are in agreement with those
predicted for the 1-D velocity model used for routine locations. For sources at offsets larger than ~5 km, the
ZLC curves depict prominent maxima associated with a secondary phase propagating with a lower velocity than
the first-arrival P-wave. Using finite-difference synthetic seismograms generated for a 2-D realistic velocity
model, we explain these late arrivals in terms of a lateral velocity variation located at depths of about 1 km. Such
discontinuity would correspond to a positive Vp anomaly imaged by a recent 3-D tomographic study, and
interpreted as the submerged southern rim of Campi Flegrei caldera collapsed during the explosive eruption of
12 Ky b.p. The small spacing among adjacent shot points allowed simultaneous wavefield decomposition at the
source and receiver arrays. Using a modified version of the double-beam method, we retrieve the independent
variation of horizontal slowness at both the source and receiver regions. For both cases, we found azimuthal
deviations as large as 50° with respect to the great circle path. At the source region, these discrepancies may be
interpreted in terms of ray bending at the interface of the aforementioned positive anomaly. At the receiver array,
the observed anomalies may be attributed to either velocity variations marking the Solfatara crater rim, or to a
near-receiver, low-velocity body whose position would coincide with negative gravimetric anomalies and a high
Vp/Vs ratio region inferred by independent geophysical and seismological studies
Morphology and depth of reflectors from 2D non-linear inversion of seismic data
We present here two methods to obtain reflection images of upper
crust seismic reflectors. The techniques are based on migration and waveform
coherence analysis of reflected seismic phases recorded in local earthquake seismograms
and in active seismic data.
The first method is a move-out and stack of reflected seismic phases in local
earthquake recordings. The theoretical travel times of reflected/converted
phases in a 1D medium for a given interface depth and velocity model are used
to align the recordings in time. The locations and origin times of events are initially
estimated from the P and S arrival times. Different seismic gathers are
obtained for each reflected/converted phase at the interface under consideration,
and the best interface depth is chosen as that which maximizes the value
of a semblance function computed on moved-out records. This method has
been applied to seismic records of microearthquakes that have occurred at the
Mt. Vesuvius volcano, and it confirms the reports of an 8- to 10-km-deep seismic
discontinuity beneath the volcano that was previously identified as the
roof of an extended magmatic sill.
The second is a non-linear 2D method for the inversion of reflection travel
times aimed at the imaging of a target upper-crust reflector. This method is specifically
designed for geophysical investigations in complex geological environments
(oil investigations, retrieving of images of volcano structures) where the
presence of complex structures makes the standard velocity analysis difficult
and degrades the quality of migrated images. Our reflector is represented by
nodes of a cubic-spline that are equally spaced at fixed horizontal locations. The
method is based on a multiscale approach and uses a global optimization technique
(genetic algorithm) that explores the whole of the parameter space, i.e.
the interface position nodes. The forward problem (the modelling of reflection
travel times) is solved using the finite-difference solver of Podvine & Lecomte
(1991) and using an a priori known background velocity model. This non-linear
method allows the automated determination of the global minimum (or maximum)
without relying on estimates of the gradient of the objective function in
the starting model and without making assumptions about the nature of the
objective function itself. We have used two types of objective functions. The
first is a least-squares L2 norm, defined as the sum of the squared differences between the observed and the calculated travel times. The second is based on
coherence measures (semblance). The main advantage of using coherence
measures is that they do not require travel-time picking to assess the degree of
fit to the data model. Thus, the time performance of the whole procedure is
improved and the subjectivity of the human operators in the picking procedure
is removed.
The methods are tested on synthetic models and have been applied to a subset
of data that was collected during the active seismic experiments performed in
September 2001 in the gulfs of Naples and Pozzuoli in the framework of what
is known as the SERAPIS project
Imaging the buried rim of Campi flegrei caldera (Italy) from array analysis
On September an extended active seismic survey(SERAPIS,Seismic Reflection
Acquisition Project for Imaging Structure)was conducted in the Gulf of Naples and
Pozzuoli with the aimof providing new insights on the Campi Flegrei caldera structure and of investigating its feeding system(fig.1).About3000air-gunsea-shots were shot(fig.3a,b,c).In the frame work of this project,anarray of 28 vertical-component and 4 three component sensors was deployed in the Solfatara crater(fig.2).The array had an
aperture of about 200m,and receivers had a natural frequency of 1Hz.An example of
the recorded wave forms is shown in figure 4
Isolation of KPC 3-producing Enterobacter aerogenes in a patient colonized by MDR Klebsiella pneumoniae
We describe the interspecies transmission of the plasmid-mediated blaKPC-3 gene, which confers carbapenem resistance, between clinically relevant gram-negative bacteria in a single patient. A KPC-3 producing Enterobacter aerogenes was isolated from a hospitalized patient previously colonized and then infected by a Klebsiella pneumoniae ST101 carrying the blaKPC-3 gene. The strains showed identical plasmids. Since intense horizontal exchanges among bacteria can occur in the gut, clinicians should be aware that patients colonized by carbapenem-resistant K. pneumoniae could become carriers of other carbapenem-resistant Enterobacteriaceae. © 2016 by Edimes - Edizioni Internazionali Srl. All rights reserved
Prevalence of molar incisor hypomineralization among school children in Rome, Italy
Molar incisor hypomineralization (MIH) is a highly prevalent condition associated with increased caries experience, dental pain and treatment need. Aim of this study was to determine the prevalence and severity of MIH in a group of 7–8 years old primary school children living in Rome, Italy; and to assess the association with caries experience and possible perinatal risk factors. A survey has been conducted in the city of Rome, between April 2019 and March 2020 with a total of 49 primary schools and 176 2nd grade primary school classes and a total of 3611 children being involved. Of these, a subset of 346 children of 21 primary schools was selected for the epidemiological investigation. The prevalence of MIH was of 18.2%, with girls showing twice the probability of being subject to a mild-severe condition. Molar location was present in 71.4%, while location on both molar plus incisor was present in 28.6% of cases. The mean DMFT was 0.44 ± 0.78, “D” was 0.17 ± 0.58; the mean dmft was 1.7 ± 2.56, “d” was 1.32 ± 2.21. Female gender, caries experience, insufficient oral hygiene were risk factors. The incidence of MIH is increasing in the pediatric population. Knowledge about diagnosis and treatment options should be disseminated among dental professionals.publishedVersio
Epidemiology and drug susceptibility of nontuberculous mycobacteria (NTM) in Italy in 2016-2020
Introduction. Nontuberculous mycobacteria (NTM) are environmental mycobacteria which may cause pulmonary and extrapulmonary diseases. These organisms are difficult to treat due to their intrinsic drug-resistance. In Italy, no major nationwide study on NTM epidemiology and drug susceptibility was performed. Methods. Data on the epidemiology of 7,469 NTM clinical isolates identified in Italy in 2016-2020 and on the minimum inhibitory concentrations (MICs) of 1,506 of these strains were analysed. Results. Overall, 63 species were identified in 42 hospital laboratories located in 16 out of 20 regions, with Mycobacterium avium complex (MAC) being the most frequently iso-lated, followed by M. gordonae, M. xenopi, M. abscessus. The MICs of 12 drugs for MAC, M. xenopi, M. kansasii, M. abscessus, M. fortuitum and M. chelonae were interpreted for clinical significance (susceptible, intermediate, resistant) based on the guidelines pub-lished by the Clinical and Laboratory Standards Institute in November 2018. Conclusions. Our data are in line with other nationwide studies and may be of value for further update of microbiological and clinical guidelines
ARRAY ANALYSIS OF AIR-GUN SEA-SHOTS RECORDS FOR IMAGING THE HIGHLY HETEROGENEOUS CRUST BENEATH CAMPI FLEGREI CALDERA (ITALY)
An extended active survey SERAPIS (Seismic Reflection
Acquisition Project for Imaging Structure)was performed on September 2001 in the Gulfs of Naples and Pozzuoli.The aim of experiment is providing new insights on the Campi
Flegrei caldera structure and investigating its feeding system (Fig.1). In the Solfatara crater (Fig.2)was deployed an array of 28
vertical-componentand 4 three-component sensors with an aperture of about 0.2km. There ceivershada natural frequency
of 1Hz. About 3000 air-gunsea-shots wereshot(Fig.3). In figure 4 are shown examples of there corded wave form s.UnpublishedPostdam, Germanyope