844 research outputs found
Wood Anderson Magnitude Scale for Mt. Vesuvius
A Mathcad-8 program to calculate a revised magnitude scale is presented. An application to Mt. Vesuvius is
included as a program test. Wood-Anderson seismograms for 131 local earthquakes recorded at station BKE
(Osservatorio Vesuviano seismic network) were synthesized to estimate local magnitude from the original
definition:
Ml=log Amax(D) - logAo(D)
The distance correction logAo(D) was empirically determined simulating a wave packet which propagates in a
structure with assigned Q.
Moment magnitude (calculated both with Kanamori and Tatcher-Hanks formulas) was also determined from
the displacement spectra.
Finally a relation between Wood-Anderson magnitude and duration magnitude was derived, allowing the
estimate of local magnitude from the duration of the earthquake
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
Re-calibration of the magnitude scales at Campi Flegrei, Italy, on the basis of measured path and site and transfer functions
The quantification of the seismic energy of earthquakes occurring in volcanic regions is of great importance in order to better understand the dynamics of the volcano. The amount of the released energy and its variation during seismic crises can be considered as an indicator of the source processes acting inside the volcano. In this context, the effect of the propagation in attenuative media should be considered to correct for path effects and to properly estimate the seismic energy released at the source. Moreover, in order to allow a comparison with the dynamic processes occurring in different volcanic areas, the use of magnitude scales as homogeneous as possible is strongly recommended,
In this framework, new duration-based Local (Ml) and Moment (Mw) magnitude scales are obtained for the Campi Flegrei area (southern Italy), by analysing a data-set of local volcano-tectonic earthquakes. First the S-wave quality factor for the investigated area was experimentally calculated and then the distance-correction curve, logA0(r), to be used in the Richter formula Ml = logAmax − logA0(r), was numerically estimated by measuring the attenuation properties and hence propagating a synthetic S-wave-packet in the earth medium. The Local magnitude scale was normalized in order to fit the Richter formula valid for Southern California at a distance of 10 km. Ml magnitude was estimated by synthesizing Wood-Anderson seismograms and measuring the maximum amplitude. For the same data-set, Moment magnitude from S-wave distance and site corrected displacement spectra was obtained. Comparisons between Local and Moment magnitudes determined in the present paper, and the old Duration magnitude (Md) routinely used at the Istituto Nazionale di Geofisica e Vulcanologia - Osservatorio Vesuviano are presented. Moreover, relationships between Ml and Mw calculated for two reference sites are also derived
Prototypes of productivity tools for the jadescript programming language
Jadescript is an agent-oriented programming language built on top of JADE. So far, the focus of the development of the language was on design choices, on syntax refinements, and on the introduction of expressions and constructs for agent-related abstractions and tasks. In this paper, a proposal to achieve the crucial goal of making Jadescript suitable for professional use is presented. The success of Jadescript, as a solid language to build real-world agent-based software systems, is necessarily related to its effective integration with mainstream development tools. In this paper, some of the productivity tools developed to integrate Jadescript with a mainstream development environment are presented as a way to promote the successful adoption of the language towards the community of JADE users
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
Attenuation and velocity structure in the area of Pozzuoli-Solfatara (Campi Flegrei, Italy) for the estimate of local site response
In the present work I infer the 1D shear-wave velocity model in the volcanic area of Pozzuoli-Solfatara using the dispersion properties of both Rayleigh waves generated by artificial explosions and microtremor. The group-velocity dispersion curves are retrieved from application of the Multiple Filter Technique (MFT) 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 (PMF). The obtained dispersion curves indicate Rayleigh-wave fundamental-mode group velocities ranging from about 0.8 to 0.6 km/sec over the 1-12 Hz frequency band.
I also propose a new approach based on the autoregressive analysis, to recover group velocity dispersion. I first present a numerical example on a synthetic test signal and then I apply the technique to the data recorded in Solfatara, in order to compare the obtained results with those inferred from the MF analysis
Moreover, I analyse ambient noise data recorded at a dense array, by using Aki’s correlation technique (SAC) and an extended version of this method (ESAC) The obtained phase velocities range from 1.5 km/s to 0.3 km/s over the 1-10 Hz frequency band.
The group velocity dispersion curves are then inverted to infer a shallow shear-wave velocity model down to a depth of about 250 m, for the area of Pozzuoli-Solfatara. The shear-wave velocities thus obtained are compatible with those derived both from cross- and down-hole measurements in neighbour wells and from laboratory experiments. These data are eventually interpreted in the light of the geological setting of the area.
I perform an attenuation study on array recordings of the signals generated by the shots. The attenuation curve was retrieved by analysing the amplitude spectral decay of Rayleigh waves with the distance, in different frequency bands. The attenuation curve was then inverted to infer the shallow Q inverse model.
Using the obtained velocity and attenuation model, I calculate the theoretical ground response to a vertically-incident SH wave obtaining two main amplification peaks centered at frequencies of 2.1 and 5.4 Hz. The transfer function was compared with those obtained experimentally from the application of Nakamura’s technique to microtremor data, artificial explosions and local earthquakes. Agreement among the transfer functions is observed only for the amplification peak of frequency 5.4 Hz.
Finally, as a complementary contribution that might be used for the assessment of seismic risk in the investigated area, I evaluate the peak ground acceleration (PGA) for the whole Campi Flegrei caldera and locally for the Pozzuoli-Solfatara area, by performing stochastic simulations of ground motion, partially constrained by the previously described results. Two different methods (random vibration theory (RVT) and ground motion generated from a Gaussian distribution (GMG)) are used, providing the PGA values of 0.04 g and 0.097 g for Campi Flegrei and Pozzuoli-Solfatara, respectively
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
Recalibration of the Magnitude Scales at Campi Flegrei, Italy, on the Basis of Measured Path and Site and Transfer Functions
New duration-based local (ML) and moment (Mw) magnitude scales are
obtained for the Campi Flegrei area through analysis of a dataset of local volcanotectonic
earthquakes. First, the S-wave quality factor for the investigated area was
experimentally calculated, and then the distance-correction curve, log A0(r), to be
used in the Richter formula ML = log Amax − log A0(r), was numerically estimated
by measuring the attenuation properties and, hence, propagating a synthetic S-wave
packet in the earth medium. The local magnitude scale was normalized to fit the
Richter formula that was valid for Southern California at a distance of 10 km. ML
was estimated by synthesizing Wood–Anderson seismograms and measuring the
maximum amplitude. For the same dataset, the moment magnitude was obtained from
S-wave distance-corrected and site-corrected displacement spectra. Comparisons
between local and moment magnitudes determined, along with the old duration
magnitude (MD) routinely used at the Istituto Nazionale di Geofisica e Vulcanologia–
Osservatorio Vesuviano, are presented and discussed. Moreover, the relationships
between ML and Mw calculated for two reference sites are also derived
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