706 research outputs found
Space-weighted seismic attenuation mapping of the aseismic source of Campi Flegrei 1983-84 unrest
Peer reviewedPublisher PD
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 â 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
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 â 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 WoodâAnderson 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 Vulcanologiaâ
Osservatorio Vesuviano, are presented and discussed. Moreover, the relationships
between ML and Mw calculated for two reference sites are also derived
Theory of controlled quantum dynamics
We introduce a general formalism, based on the stochastic formulation of
quantum mechanics, to obtain localized quasi-classical wave packets as
dynamically controlled systems, for arbitrary anharmonic potentials. The
control is in general linear, and it amounts to introduce additional quadratic
and linear time-dependent terms to the given potential. In this way one can
construct for general systems either coherent packets moving with constant
dispersion, or dynamically squeezed packets whose spreading remains bounded for
all times. In the standard operatorial framework our scheme corresponds to a
suitable generalization of the displacement and scaling operators that generate
the coherent and squeezed states of the harmonic oscillator.Comment: LaTeX, A4wide, 28 pages, no figures. To appear in J. Phys. A: Math.
Gen., April 199
Seismic energy envelopes in volcanic media : in need of boundary conditions
Peer reviewedPublisher PD
Multiple resolution seismic attenuation imaging at Mt. Vesuvius
A three-dimensional S wave attenuation tomography of Mt. Vesuvius has been ob-
tained with multiple measurements of coda-normalized S-wave spectra of local small
magnitude earthquakes. We used 6609 waveforms, relative to 826 volcano-tectonic
earthquakes, located close to the crater axis in a depth range between 1 and 4 km
(below the sea level), recorded at seven 3-component digital seismic stations. We
adopted a two-point ray-tracing; rays were traced in an high resolution 3-D velocity
model. The spatial resolution achieved in the attenuation tomography is comparable
with that of the velocity tomography (we resolve 300 m side cubic cells). We statisti-
cally tested that the results are almost independent from the radiation pattern. We
also applied an improvement of the ordinary spectral-slope method to both P- and
S-waves, assuming that the di€erences between the theoretical and the experimental
high frequency spectral-slope are only due to the attenuation e€ects.We could check
the coda-normalization method comparing the S attenuation image obtained with
the two methods. The images were obtained with a multiple resolution approach.
Results show the general coincidence of low attenuation with high velocity zones.
The joint interpretation of velocity and attenuation images allows us to interpret
the low attenuation zone intruding toward the surface until a depth of 500 meters
below the sea level as related to the residual part of solidi ed magma from the last
eruption. In the depth range between -700 and -2300 meters above sea level, the
images are consistent with the presence of multiple acquifer layers. No evidence of
magma patches greater than the minimum cell dimension (300m) has been found.
A shallow P wave attenuation anomaly (beneath the southern ank of the volcano)
is consitent with the presence of gas saturated rocks. The zone characterized by
the maximum seismic energy release cohincides with a high attenuation and low
velocity volume, interpreted as a cracked medium
Earthquake Characteristics and Structural Properties of the Southern Tyrrhenian Basin from Full Seismic Wave Simulations
Modelling the response of seismic wavefields to sharp lateral variations in crustal discontinuities is essential for seismic tomography application and path effects correction in earthquake source characterization. This is particularly relevant when wavefields cross back-arc oceanic basins, i.e. mixed continental-oceanic settings. High-frequency (> 0.05 Hz) seismic waves resonate and get absorbed across these settings due to a shallow Moho, crustal heterogeneities, and energy leakage. Here, we provide the first high-frequency wave-equation model of full seismograms propagating through realistic 3D back-arc basins. Inversion by parameters trial based on correlation analyses identifies P-, S-and coda-wave as attributes able to estimate jointly 3D Moho variations, sediment thickness, and earthquake source characteristics using data from a single regional earthquake. We use as data waveforms produced by the Accumoli earthquake (Central Italy, 2016), propagating across the Southern Tyrrhenian basin and recorded across Southern Italy. The best model comprises a deep Moho ( similar to 18 km) in the middle of the basin and a crustal pinch with the continental crust in Sicily. The deep Moho corresponds to the Issel Bridge, a portion of continental crust trapped between the Vavilov and Marsili volcanic centres. The Accumoli earthquake is optimally described at a depth of 7.3 km using a boxcar with rise time of 6 s. Our results show that the early S-wave coda comprises trapped and reverberating phases sensitive to crustal interfaces. Forward modelling these waves is computationally expensive; however, adding these attributes to tomographic procedures allows modelling both source and structural parameters across oceanic basins
DYNAMICAL CONTROL OF THE HALO IN PARTICLE BEAMS: A STOCHASTICâHYDRODYNAMIC APPROACH
In this paper we describe the beam distribution in particle accelerators in the framework of a stochasticâhydrodynamic scheme. In this scheme the possible reproduction of the halo after its elimination is a consequence of the stationarity of the transverse distribution which plays the role of an attractor for every other distribution. The relaxation time toward the halo is estimated, and a few examples of controlled transitions toward a permanent halo elimination are discussed
A stochastic-hydrodynamic model of halo formation in charged particle beams
The formation of the beam halo in charged particle accelerators is studied in
the framework of a stochastic-hydrodynamic model for the collective motion of
the particle beam. In such a stochastic-hydrodynamic theory the density and the
phase of the charged beam obey a set of coupled nonlinear hydrodynamic
equations with explicit time-reversal invariance. This leads to a linearized
theory that describes the collective dynamics of the beam in terms of a
classical Schr\"odinger equation. Taking into account space-charge effects, we
derive a set of coupled nonlinear hydrodynamic equations. These equations
define a collective dynamics of self-interacting systems much in the same
spirit as in the Gross-Pitaevskii and Landau-Ginzburg theories of the
collective dynamics for interacting quantum many-body systems. Self-consistent
solutions of the dynamical equations lead to quasi-stationary beam
configurations with enhanced transverse dispersion and transverse emittance
growth. In the limit of a frozen space-charge core it is then possible to
determine and study the properties of stationary, stable core-plus-halo beam
distributions. In this scheme the possible reproduction of the halo after its
elimination is a consequence of the stationarity of the transverse distribution
which plays the role of an attractor for every other distribution.Comment: 18 pages, 20 figures, submitted to Phys. Rev. ST A
Controlled quantum evolutions and transitions
We study the nonstationary solutions of Fokker-Planck equations associated to
either stationary or nonstationary quantum states. In particular we discuss the
stationary states of quantum systems with singular velocity fields. We
introduce a technique that allows to realize arbitrary evolutions ruled by
these equations, to account for controlled quantum transitions. The method is
illustrated by presenting the detailed treatment of the transition
probabilities and of the controlling time-dependent potentials associated to
the transitions between the stationary, the coherent, and the squeezed states
of the harmonic oscillator. Possible extensions to anharmonic systems and mixed
states are briefly discussed and assessed.Comment: 24 pages, 4 figure
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