646 research outputs found
Photometric and spectroscopic study of the intermediate-age open cluster NGC 2355
In this paper we analyse the evolutionary status and properties of the old
open cluster NGC 2355, located in the Galactic anticentre direction, as a part
of the long term programme BOCCE. NGC 2355 was observed with LBC@LBT using the
Bessel , , and filters. The cluster parameters have been obtained
using the synthetic colour-magnitude diagram (CMD) method, as done in other
papers of this series. Additional spectroscopic observations with FIES@NOT of
three giant stars were used to determine the chemical properties of the
cluster. Our analysis shows that NGC 2355 has metallicity slightly less than
solar, with [Fe/H] dex, age between 0.8 and 1 Gyr, reddening
in the range 0.14 and 0.19 mag, and distance modulus of about 11 mag.
We also investigated the abundances of O, Na, Al, , iron-peak, and
neutron capture elements, showing that NGC 2355 falls within the abundance
distribution of similar clusters (same age and metallicity). The Galactocentric
distance of NGC~2355 places it at the border between two regimes of metallicity
distribution; this makes it an important cluster for the study of the chemical
properties and evolution of the disc.Comment: 20 pages, 11 figures, Accepted on MNRA
New constraints for site-effect characterization from seismic noise
In the framework of ground-motion amplification analysis for southern
Italy, the main target of this study is to provide new constraints on onedimensional,
shallow-velocity profiles for a site in the San Fele area
near the city of Potenza (southern Italy) where a permanent Irpinia
Seismic Network (ISNet) seismic station is installed. Ambient noise
vibrations were recorded during a seismic survey in San Fele, and the
data acquired were used to define the shallow shear-wave velocity
profiles and thicknesses of the shallow soil layers, through analysis of
the dispersion characteristics of the surface waves. Single station and
array techniques were used to obtain robust results, which show
relatively flat curves of the H/V spectral ratios and variations in shearwave
velocities confined to the first 50 m in depth. On the basis of these
results for the San Fele site, the present study aims to delineate a
standard procedure that can be systematically applied to all of the other
ISNet stations to improve site characterization. This will allow more
accurate evaluation of peak ground-motion quantities (e.g. peak
ground acceleration, peak ground velocity) at rock sites for use in shakemap
analysis
Shallow shear-wave velocity structure of Solfatara volcano (Campi Flegrei, Italy),from inversion of Rayleigh-wave dispersion curves
In this work, we infer the 1D shear-wave velocity model at Solfatara volcano using the
dispersion properties of Rayleigh waves generated by artificial explosions. The groupvelocity
dispersion curves are retrieved by applying the Multiple Filter Technique to
single-station recordings of air-gun sea shots. Seismic signals are filtered in different
frequency bands and the dispersion curves are obtained by evaluating the arrival times
of the envelope maxima of the filtered signals. Fundamental and higher modes are
carefully recognized and separated by using a Phase Matched Filter. The dispersion
curves obtained indicate Rayleigh-wave fundamental-mode group velocities ranging
from about 0.8 to 0.6 km/s over the 2-12 Hz frequency band. These group velocity
dispersion curves are then inverted to infer a shallow shear-wave velocity model down
to a depth of about 250 m. The shear-wave velocities thus obtained are compatible
with those derived both from cross- and down-hole measurements in neighbouring
wells and from laboratory experiments. These data are eventually interpreted in the
light of the geological setting of the area. Using the velocity model obtained, we
calculate the theoretical ground response to a vertically-incident S-wave getting two,
main amplification peaks centered at frequencies of 2.2 and 5.4 Hz. The transfer
function was compared to those obtained experimentally from the application of
Nakamura’s technique to microtremor data, artificial explosions and local
earthquakes. Agreement among the experimental and theoretical transfer functions is
observed for the amplification peak of frequency 5.4 Hz
Seismic activity and thermal regime of low temperature fumaroles at Mt. Vesuvius in 2004-2011: distinguishing among seismic, volcanic and hydrological signals
Seismological, soil temperature and hydrological data from Mt. Vesuvius are collected to characterize the present-day activity of the volcanic/hydrothermal system and to detect possible unrest-related phenomena. We present patterns of seismicity and soil temperature in the crater area during the period February 2004-December 2011. The temporal distribution of number and depth of Volcano-Tectonic earthquakes and the energy release are considered. Hourly data of soil temperature have been acquired since January 2004 in different locations along the rim and within the crater. The observed changes of temperature are studied to establish a temporal-based correlation with the volcanic activity and/or with external forcing, as variations of the regional and local stress field acting on the volcano or meteorological phenomena. The comparison between seismic activity and temperature data highlights significant variations possibly related to changes in fluid circulation in the hydrothermal system of the volcano. The common continuous observations start just before a very shallow earthquake occurred in August 2005, which was preceded by a thermal anomaly. This coincidence has been interpreted as related to fluid-driven rock fracturing, as observed in other volcanoes. For the successive temporal patterns, the seismicity rate and energy release are characterized by slight variations accompanied by changes in temperature. This evidence of reactivity of the fumarole thermal field to seismic strain can be used to discriminate between tectonic and volcanic signals at Mt. Vesuvius
Groundwater geochemistry of the Mt. Vesuvius area: implications for volcano surveillance and relationship with hydrological and seismic signals
Geochemical data obtained between 1998 and 2011 at the Mt. Vesuvius
aquifer are discussed, focusing on the effects of both the hydrological
regime and the temporal pattern of local seismicity. Water samples were
collected in a permanent network of wells and springs located in the areas
that are mostly affected by the ascent of magmatic volatiles, and their
chemical composition and dissolved gas content were analyzed. As well as
the geochemical parameters that describe the behavior of groundwater at
Mt. Vesuvius, we discuss the temporal distribution of volcano-tectonic
earthquakes. The seismological data set was collected by the stations
forming the permanent and mobile network of the Istituto Nazionale
di Geofisica e Vulcanologia - Osservatorio Vesuviano (INGV-OV). Our
analysis of seismic data collected during 1998-2011 identified statistically
significant variations in the seismicity rate, marked by phases of decreasing
activity from October 1999 to May 2001 and increasing activity
from August 2004 to mid-2006. The water chemistry shows peculiar patterns,
characterized by a changeable input of CO2-rich and saline water,
which must be related to either a changing stress field or an increased
input of CO2-rich vapor. The water chemistry data from 1999 to 2003 account
for both higher fluid pressure (which induced the seismic crisis of
1999 that peaked with a 3.6-magnitude earthquake in October 1999) and
the increased input of CO2-rich fluids. The highest emission of CO2 from
the crater fumaroles and the corresponding increase in dissolved carbon
in groundwater characterize the phase of low seismicity. The termination
of the phase of intense deep degassing is associated with a change in
water chemistry and a peculiar seismic event that was recorded in July
2003. All these seismic and geochemical patterns are interpreted according
to temporal variations in the regional and local stress field
Large Binocular Telescope observations of PSR J2043+2740
We present the results of deep optical imaging of the radio/-ray
pulsar PSR J2043+2740, obtained with the Large Binocular Telescope (LBT). With
a characteristic age of 1.2 Myr, PSR J2043+2740 is one of the oldest (non
recycled) pulsars detected in -rays, although with still a quite high
rotational energy reservoir ( erg
s). The presumably close distance (a few hundred pc), suggested by the
hydrogen column density ( cm),
would make it a viable target for deep optical observations, never attempted
until now. We observed the pulsar with the Large Binocular Camera of the LBT.
The only object (V=25.440.05) detected within ~3" from the pulsar radio
coordinates is unrelated to it. PSR J2043+2740 is, thus, undetected down to
V~26.6 (3-), the deepest limit on its optical emission. We discuss the
implications of this result on the pulsar emission properties.Comment: 4 pages, 3 figures, accepted for publication on MNRA
Seasonal and event-based hydrological and slope stability modeling of pyroclastic fall deposits covering slopes in Campania (Southern Italy)
The pyroclastic fall deposits mantling mountain slopes in the Campania region (Southern Italy) represent one of the most studied geomorphological frameworks of the world regarding rainfall-induced debris flows threating urban areas. The proposed study focused on advancing knowledge about the hydrological response of pyroclastic fall coverings from the seasonal to event-based time scales, leading to the initiation of slope instability. The study was based on two consequential tasks. The first was the analysis of a six-year monitoring of soil pressure head carried out in a sample area of the Sarno Mountains, located above a debris flow initiation zone. The second was based on coupled hydrological and slope stability modeling performed on the physical models of slopes, which were reconstructed by empirical correlations between the slope angle, total thickness, and stratigraphic settings of pyroclastic fall deposits mantling slopes. The results obtained were: (a) The understanding of a soil pressure head regime of the volcaniclastic soil mantle, always ranging in unsaturated conditions and characterized by a strong seasonal variability depending on precipitation patterns and the life cycle of deciduous chestnut forest; and (b) the reconstruction through a deterministic approach of seasonal intensity-duration rainfall thresholds related to different morphological conditions
The first Long Period earthquake detected in the background seismicity at Mt. Vesuvius
The typical earthquakes occurring at Mt. Vesuvius are Volcano-Tectonic. On July 20, 2003, an unusual earthquake with low and narrow frequency content was detected. The seismograms presented an emergent onset and a nearly monochromatic spectrum at all stations of the Osservatorio Vesuviano(Istituto Nazionale di Geofisica e Vulcanologia) seismic network. The event was located at about 4 km b.s.l. close to the crater axis and an equivalent duration magnitude of 0.6 was estimated. The nature of this event was investigated by comparing its features with those of two typical
Volcano-Tectonic earthquakes occurred inside the same source volume. We compared the spectral content calculating the spectrograms and the coda patterns using the Hilbert Transform. A Seismic Moment Tensor inversion was performed on the low frequency earthquake. The focal mechanisms for the two Volcano-Tectonic earthquakes were estimated with a classical technique and resulted compatible with the stress field acting on the volcano. Taking into account the clear differences with the typical Volcano-Tectonic events as well as the peculiarities retrieved from our analyses (monochromatic, low frequency spectral content, and sustained coda) and also some geochemical observations, we classify the unusual low frequency seismic event detected at Mt. Vesuvius as Long Period earthquake and propose that its origin could be linked to a pressure drop in the deep hydrothermal system
Testing evapotranspiration estimates based on MODIS satellite data in the assessment of the groundwater recharge of karst aquifers in southern Italy
In many Italian regions, and particularly in southern Italy, karst aquifers are the main sources of drinking water and play a crucial role in the socio-economic development of the territory. Hence, estimating the groundwater recharge of these aquifers is a fundamental task for the proper management of water resources, while also considering the impacts of climate changes. In the southern Apennines, the assessment of hydrological parameters that is needed for the estimation of groundwater recharge is a challenging issue, especially for the spatial and temporal inhomogeneity of networks of rain and air temperature stations, as well as the variable geomorphological features and land use across mountainous karst areas. In such a framework, the integration of terrestrial and remotely sensed data is a promising approach to limit these uncertainties. In this research, estimations of actual evapotranspiration and groundwater recharge using remotely sensed data gathered by the Moderate Resolution Imaging Spectrometer (MODIS) satellite in the period 2000–2014 are shown for karst aquifers of the southern Apennines. To assess the uncertainties affecting conventional methods based on empirical formulas, the values estimated by the MODIS dataset were compared with those calculated by Coutagne, Turc, and Thornthwaite classical empirical formulas, which were based on the recordings of meteorological stations. The annual rainfall time series of 266 rain gauges and 150 air temperature stations, recorded using meteorological networks managed by public agencies in the period 2000–2014, were considered for reconstructing the regional distributed models of actual evapotranspiration (AET) and groundwater recharge. Considering the MODIS AET, the mean annual groundwater recharge for karst aquifers was estimated to be about 448 mm·year−1 . In contrast, using the Turc, Coutagne, and Thornthwaite methods, it was estimated as being 494, 533, and 437 mm·year−1, respectively. The obtained results open a new methodological perspective for the assessment of the groundwater recharge of karst aquifers at the regional and mean annual scales, allowing for limiting uncertainties and taking into account a spatial resolution greater than that of the existing meteorological networks. Among the most relevant results obtained via the comparison of classical approaches used for estimating evapotranspiration is the good matching of the actual evapotranspiration estimated using MODIS data with the potential evapotranspiration estimated using the Thornthwaite formula. This result was considered linked to the availability of soil moisture for the evapotranspiration demand due to the relevant precipitation in the area, the general occurrence of soils covering karst aquifers, and the dense vegetation
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