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A comprehensive study of the 26th December 2004 Sumatra earthquake: possible implications on Earth rotation and investigations on the coseismic and postseismic stress diffusion associated with the seismic rupturePisani, Anna Rita <1973> 09 June 2008 (has links)
In this work a multidisciplinary study of the December 26th, 2004 Sumatra
earthquake has been carried out. We have investigated both the effect of the
earthquake on the Earth rotation and the stress field variations associated
with the seismic event.
In the first part of the work we have quantified the effects of a water
mass redistribution associated with the propagation of a tsunami wave on the
Earth’s pole path and on the length-of-day (LOD) and applied our modeling
results to the tsunami following the 2004 giant Sumatra earthquake. We
compared the result of our simulations on the instantaneous rotational axis
variations with some preliminary instrumental evidences on the pole path
perturbation (which has not been confirmed yet) registered just after the
occurrence of the earthquake, which showed a step-like discontinuity that
cannot be attributed to the effect of a seismic dislocation.
Our results show that the perturbation induced by the tsunami on the
instantaneous rotational pole is characterized by a step-like discontinuity,
which is compatible with the observations but its magnitude turns out to be
almost one hundred times smaller than the detected one. The LOD variation
induced by the water mass redistribution turns out to be not significant because the total effect is smaller than current measurements uncertainties.
In the second part of this work of thesis we modeled the coseismic and
postseismic stress evolution following the Sumatra earthquake. By means of
a semi-analytical, viscoelastic, spherical model of global postseismic deformation
and a numerical finite-element approach, we performed an analysis
of the stress diffusion following the earthquake in the near and far field of
the mainshock source. We evaluated the stress changes due to the Sumatra
earthquake by projecting the Coulomb stress over the sequence of aftershocks
taken from various catalogues in a time window spanning about two years
and finally analyzed the spatio-temporal pattern.
The analysis performed with the semi-analytical and the finite-element
modeling gives a complex picture of the stress diffusion, in the area under
study, after the Sumatra earthquake. We believe that the results obtained
with the analytical method suffer heavily for the restrictions imposed, on the
hypocentral depths of the aftershocks, in order to obtain the convergence of
the harmonic series of the stress components. On the contrary we imposed no
constraints on the numerical method so we expect that the results obtained
give a more realistic description of the stress variations pattern.
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Joint inversion of GPS and strong motion data for earthquake rupture modelsCirella, Antonella <1977> 09 June 2008 (has links)
No description available.
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Shallow and deep deformation in northern Apennines region using seismological dataSalimbeni, Simone <1974> 09 June 2008 (has links)
For its particular position and the complex geological history, the Northern Apennines has
been considered as a natural laboratory to apply several kinds of investigations. By the
way, it is complicated to joint all the knowledge about the Northern Apennines in a unique
picture that explains the structural and geological emplacement that produced it. The main
goal of this thesis is to put together all information on the deformation - in the crust and at
depth - of this region and to describe a geodynamical model that takes account of it.
To do so, we have analyzed the pattern of deformation in the crust and in the mantle. In
both cases the deformation has been studied using always information recovered from
earthquakes, although using different techniques. In particular the shallower deformation
has been studied using seismic moment tensors information. For our purpose we used the
methods described in Arvidsson and Ekstrom (1998) that allowing the use in the inversion
of surface waves [and not only of the body waves as the Centroid Moment Tensor
(Dziewonski et al., 1981) one] allow to determine seismic source parameters for
earthquakes with magnitude as small as 4.0. We applied this tool in the Northern
Apennines and through this activity we have built up the Italian CMT dataset (Pondrelli et
al., 2006) and the pattern of seismic deformation using the Kostrov (1974) method on a
regular grid of 0.25 degree cells. We obtained a map of lateral variations of the pattern of
seismic deformation on different layers of depth, taking into account the fact that shallow
earthquakes (within 15 km of depth) in the region occur everywhere while most of events
with a deeper hypocenter (15-40 km) occur only in the outer part of the belt, on the Adriatic
side. For the analysis of the deep deformation, i.e. that occurred in the mantle, we used
the anisotropy information characterizing the structure below the Northern Apennines. The
anisotropy is an earth properties that in the crust is due to the presence of aligned fluid
filled cracks or alternating isotropic layers with different elastic properties while in the
mantle the most important cause of seismic anisotropy is the lattice preferred orientation
(LPO) of the mantle minerals as the olivine. This last is a highly anisotropic mineral and
tends to align its fast crystallographic axes (a-axis) parallel to the astenospheric flow as a
response to finite strain induced by geodynamic processes. The seismic anisotropy pattern
of a region is measured utilizing the shear wave splitting phenomenon (that is the
seismological analogue to optical birefringence). Here, to do so, we apply on teleseismic
earthquakes recorded on stations located in the study region, the Sileny and Plomerova
(1996) approach. The results are analyzed on the basis of their lateral and vertical
variations to better define the earth structure beneath Northern Apennines. We find
different anisotropic domains, a Tuscany and an Adria one, with a pattern of seismic
anisotropy which laterally varies in a similar way respect to the seismic deformation.
Moreover, beneath the Adriatic region the distribution of the splitting parameters is so
complex to request an appropriate analysis. Therefore we applied on our data the code of
Menke and Levin (2003) which allows to look for different models of structures with
multilayer anisotropy. We obtained that the structure beneath the Po Plain is probably
even more complicated than expected. On the basis of the results obtained for this thesis,
added with those from previous works, we suggest that slab roll-back, which created the
Apennines and opened the Tyrrhenian Sea, evolved in the north boundary of Northern
Apennines in a different way from its southern part. In particular, the trench retreat
developed primarily south of our study region, with an eastward roll-back. In the northern
portion of the orogen, after a first stage during which the retreat was perpendicular to the
trench, it became oblique with respect to the structure.
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Estimating crustal deformation from geodetic dataCheloni, Daniele <1979> 09 June 2008 (has links)
By the end of the 19th century, geodesy has contributed greatly to the knowledge of regional
tectonics and fault movement through its ability to measure, at sub-centimetre precision, the
relative positions of points on the Earth’s surface. Nowadays the systematic analysis of
geodetic measurements in active deformation regions represents therefore one of the most
important tool in the study of crustal deformation over different temporal scales [e.g., Dixon,
1991]. This dissertation focuses on motion that can be observed geodetically with classical
terrestrial position measurements, particularly triangulation and leveling observations. The
work is divided into two sections: an overview of the principal methods for estimating longterm
accumulation of elastic strain from terrestrial observations, and an overview of the
principal methods for rigorously inverting surface coseismic deformation fields for source
geometry with tests on synthetic deformation data sets and applications in two different
tectonically active regions of the Italian peninsula. For the long-term accumulation of elastic
strain analysis, triangulation data were available from a geodetic network across the Messina
Straits area (southern Italy) for the period 1971 – 2004. From resulting angle changes, the
shear strain rates as well as the orientation of the principal axes of the strain rate tensor were
estimated. The computed average annual shear strain rates for the time period between 1971
and 2004 are γ˙1 = 113.89 ± 54.96 nanostrain/yr and γ˙2 = -23.38 ± 48.71 nanostrain/yr, with
the orientation of the most extensional strain (θ) at N140.80° ± 19.55°E. These results
suggests that the first-order strain field of the area is dominated by extension in the direction
perpendicular to the trend of the Straits, sustaining the hypothesis that the Messina Straits
could represents an area of active concentrated deformation. The orientation of θ agree well
with GPS deformation estimates, calculated over shorter time interval, and is consistent with
previous preliminary GPS estimates [D’Agostino and Selvaggi, 2004; Serpelloni et al., 2005]
and is also similar to the direction of the 1908 (MW 7.1) earthquake slip vector [e.g., Boschi et
al., 1989; Valensise and Pantosti, 1992; Pino et al., 2000; Amoruso et al., 2002]. Thus, the
measured strain rate can be attributed to an active extension across the Messina Straits,
corresponding to a relative extension rate ranges between < 1mm/yr and up to ~ 2 mm/yr,
within the portion of the Straits covered by the triangulation network. These results are
consistent with the hypothesis that the Messina Straits is an important active geological
boundary between the Sicilian and the Calabrian domains and support previous preliminary
GPS-based estimates of strain rates across the Straits, which show that the active deformation
is distributed along a greater area. Finally, the preliminary dislocation modelling has shown
that, although the current geodetic measurements do not resolve the geometry of the
dislocation models, they solve well the rate of interseismic strain accumulation across the
Messina Straits and give useful information about the locking the depth of the shear zone.
Geodetic data, triangulation and leveling measurements of the 1976 Friuli (NE Italy)
earthquake, were available for the inversion of coseismic source parameters. From observed
angle and elevation changes, the source parameters of the seismic sequence were estimated in
a join inversion using an algorithm called “simulated annealing”. The computed optimal
uniform–slip elastic dislocation model consists of a 30° north-dipping shallow (depth 1.30 ±
0.75 km) fault plane with azimuth of 273° and accommodating reverse dextral slip of about
1.8 m. The hypocentral location and inferred fault plane of the main event are then consistent
with the activation of Periadriatic overthrusts or other related thrust faults as the Gemona-
Kobarid thrust. Then, the geodetic data set exclude the source solution of Aoudia et al. [2000],
Peruzza et al. [2002] and Poli et al. [2002] that considers the Susans-Tricesimo thrust as the
May 6 event. The best-fit source model is then more consistent with the solution of Pondrelli
et al. [2001], which proposed the activation of other thrusts located more to the North of the
Susans-Tricesimo thrust, probably on Periadriatic related thrust faults. The main
characteristics of the leveling and triangulation data are then fit by the optimal single fault
model, that is, these results are consistent with a first-order rupture process characterized by a
progressive rupture of a single fault system. A single uniform-slip fault model seems to not
reproduce some minor complexities of the observations, and some residual signals that are not
modelled by the optimal single-fault plane solution, were observed. In fact, the single fault
plane model does not reproduce some minor features of the leveling deformation field along
the route 36 south of the main uplift peak, that is, a second fault seems to be necessary to
reproduce these residual signals. By assuming movements along some mapped thrust located
southward of the inferred optimal single-plane solution, the residual signal has been
successfully modelled. In summary, the inversion results presented in this Thesis, are
consistent with the activation of some Periadriatic related thrust for the main events of the
sequence, and with a minor importance of the southward thrust systems of the middle
Tagliamento plain.
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The attenuation of seismic intensityPasolini, Chiara <1980> 20 June 2008 (has links)
No description available.
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Seismic wave modelling for large scale 3-D problems: method development and application to lateral heterogeneity imagingDanecek, Peter <1971> 20 June 2008 (has links)
No description available.
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Multiresolution spherical wavelet analysis in global seismic tomographyCarannante, Simona <1976> 20 June 2008 (has links)
Every seismic event produces seismic waves which travel throughout the Earth.
Seismology is the science of interpreting measurements to derive information about the structure of the
Earth. Seismic tomography is the most powerful tool for determination of 3D structure of deep Earth's
interiors. Tomographic models obtained at the global and regional scales are an underlying tool for
determination of geodynamical state of the Earth, showing evident correlation with other geophysical and
geological characteristics. The global tomographic images of the Earth can be written as a linear
combinations of basis functions from a specifically chosen set, defining the model parameterization. A
number of different parameterizations are commonly seen in literature: seismic velocities in the Earth
have been expressed, for example, as combinations of spherical harmonics or by means of the simpler
characteristic functions of discrete cells.
With this work we are interested to focus our attention on this aspect, evaluating a new type of
parameterization, performed by means of wavelet functions. It is known from the classical Fourier theory
that a signal can be expressed as the sum of a, possibly infinite, series of sines and cosines. This sum is
often referred as a Fourier expansion. The big disadvantage of a Fourier expansion is that it has only
frequency resolution and no time resolution.
The Wavelet Analysis (or Wavelet Transform) is probably the most recent solution to overcome the
shortcomings of Fourier analysis. The fundamental idea behind this innovative analysis is to study signal
according to scale. Wavelets, in fact, are mathematical functions that cut up data into different frequency
components, and then study each component with resolution matched to its scale, so they are especially
useful in the analysis of non stationary process that contains multi-scale features, discontinuities and
sharp strike. Wavelets are essentially used in two ways when they are applied in geophysical process or
signals studies: 1) as a basis for representation or characterization of process; 2) as an integration kernel
for analysis to extract information about the process.
These two types of applications of wavelets in geophysical field, are object of study of this work.
At the beginning we use the wavelets as basis to represent and resolve the Tomographic Inverse
Problem. After a briefly introduction to seismic tomography theory, we assess the power of wavelet
analysis in the representation of two different type of synthetic models; then we apply it to real data,
obtaining surface wave phase velocity maps and evaluating its abilities by means of comparison with an
other type of parametrization (i.e., block parametrization).
For the second type of wavelet application we analyze the ability of Continuous Wavelet Transform
in the spectral analysis, starting again with some synthetic tests to evaluate its sensibility and capability
and then apply the same analysis to real data to obtain Local Correlation Maps between different model
at same depth or between different profiles of the same model.
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Sviluppo di metodologie di localizzazione nel contesto del Comprehensive Nuclear Test-Ban TreatyGiuntini, Alessandra <1976> 20 June 2008 (has links)
Since the first underground nuclear explosion, carried out in 1958, the analysis of seismic
signals generated by these sources has allowed seismologists to refine the travel times of seismic
waves through the Earth and to verify the accuracy of the location algorithms (the ground truth for
these sources was often known). Long international negotiates have been devoted to limit the
proliferation and testing of nuclear weapons. In particular the Treaty for the comprehensive nuclear
test ban (CTBT), was opened to signatures in 1996, though, even if it has been signed by 178
States, has not yet entered into force, The Treaty underlines the fundamental role of the
seismological observations to verify its compliance, by detecting and locating seismic events, and
identifying the nature of their sources. A precise definition of the hypocentral parameters represents
the first step to discriminate whether a given seismic event is natural or not. In case that a specific
event is retained suspicious by the majority of the State Parties, the Treaty contains provisions for
conducting an on-site inspection (OSI) in the area surrounding the epicenter of the event, located
through the International Monitoring System (IMS) of the CTBT Organization. An OSI is supposed
to include the use of passive seismic techniques in the area of the suspected clandestine
underground nuclear test. In fact, high quality seismological systems are thought to be capable to
detect and locate very weak aftershocks triggered by underground nuclear explosions in the first
days or weeks following the test.
This PhD thesis deals with the development of two different seismic location techniques: the
first one, known as the double difference joint hypocenter determination (DDJHD) technique, is
aimed at locating closely spaced events at a global scale. The locations obtained by this method are
characterized by a high relative accuracy, although the absolute location of the whole cluster
remains uncertain. We eliminate this problem introducing a priori information: the known location
of a selected event. The second technique concerns the reliable estimates of back azimuth and
apparent velocity of seismic waves from local events of very low magnitude recorded by a trypartite
array at a very local scale. For the two above-mentioned techniques, we have used the crosscorrelation
technique among digital waveforms in order to minimize the errors linked with incorrect
phase picking. The cross-correlation method relies on the similarity between waveforms of a pair of
events at the same station, at the global scale, and on the similarity between waveforms of the same
event at two different sensors of the try-partite array, at the local scale.
After preliminary tests on the reliability of our location techniques based on simulations, we
have applied both methodologies to real seismic events. The DDJHD technique has been applied to
a seismic sequence occurred in the Turkey-Iran border region, using the data recorded by the IMS.
At the beginning, the algorithm was applied to the differences among the original arrival times of
the P phases, so the cross-correlation was not used. We have obtained that the relevant geometrical
spreading, noticeable in the standard locations (namely the locations produced by the analysts of the
International Data Center (IDC) of the CTBT Organization, assumed as our reference), has been
considerably reduced by the application of our technique. This is what we expected, since the
methodology has been applied to a sequence of events for which we can suppose a real closeness
among the hypocenters, belonging to the same seismic structure. Our results point out the main
advantage of this methodology: the systematic errors affecting the arrival times have been removed
or at least reduced. The introduction of the cross-correlation has not brought evident improvements
to our results: the two sets of locations (without and with the application of the cross-correlation
technique) are very similar to each other. This can be commented saying that the use of the crosscorrelation
has not substantially improved the precision of the manual pickings. Probably the
pickings reported by the IDC are good enough to make the random picking error less important than
the systematic error on travel times. As a further justification for the scarce quality of the results
given by the cross-correlation, it should be remarked that the events included in our data set don’t
have generally a good signal to noise ratio (SNR): the selected sequence is composed of weak
events ( magnitude 4 or smaller) and the signals are strongly attenuated because of the large
distance between the stations and the hypocentral area.
In the local scale, in addition to the cross-correlation, we have performed a signal
interpolation in order to improve the time resolution. The algorithm so developed has been applied
to the data collected during an experiment carried out in Israel between 1998 and 1999. The results
pointed out the following relevant conclusions: a) it is necessary to correlate waveform segments
corresponding to the same seismic phases; b) it is not essential to select the exact first arrivals; and
c) relevant information can be also obtained from the maximum amplitude wavelet of the
waveforms (particularly in bad SNR conditions).
Another remarkable point of our procedure is that its application doesn’t demand a long time
to process the data, and therefore the user can immediately check the results. During a field survey,
such feature will make possible a quasi real-time check allowing the immediate optimization of the
array geometry, if so suggested by the results at an early stage.
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Educare la democrazia. Educativo e politico nella tradizione liberaleBiagini, Marco <1960> 21 April 2008 (has links)
La presente ricerca si basa sull’ipotesi che all’interno della tradizione liberale il
momento educativo sia tanto importante quanto quello politico. E’ una tesi che non
trova molti riscontri nella letteratura intorno al liberalismo, maggiormente propensa a
vedere in ogni intervento formativo una minaccia alla libera espressione individuale.
L’educazione, secondo questa accezione, conterrebbe una rilevante disposizione ad
essere utilizzata ideologicamente, finendo per divenire il più raffinato degli strumenti
illiberali.
Nel tentativo di contrastare tale ipotesi sono analizzate le principali manifestazioni
del liberalismo: contrattualistico (Locke), evoluzionistico (Mandeville, Hume,
Smith), giuridico-morale (Kant), liberal-democratico (Tocqueville) e sociale
(Dewey). Da tale analisi emerge un particolare modello pedagogico, di natura
indiretta e asistematica, che pone al centro della propria riflessione la salvaguardia
delle prerogative individuali, senza che questo comporti la sottovalutazione della
presenza dell’altro e della creazione di istituzioni sociali giuste. Il processo educativo,
inoltre, non può essere visto secondo un’ottica propedeutica nei confronti
dell’esperienza politica, contenendo al proprio interno quelle variabili di ordine
comportamentale e relazionale in grado di anticipare la stessa vita democratica.
Quest’ultima, secondo la celebre definizione di Dewey, non può che essere devota
nei confronti dell’educazione, non potendo basarsi esclusivamente su giustificazioni
di ordine formale. Il discorso intorno al processo formativo, di conseguenza,
allontana il pericolo che il progetto politico liberale si tramuti in mero disegno di
stampo “ingegneristico”, senza alcuna considerazione intorno al piano della
realizzabilità.
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Traduzioni di opéras-comiques nella Biblioteca Estense Universitaria di Modena: il Riccardo Cor di LeoneBugani, Fabrizio <1966> 23 June 2008 (has links)
No description available.
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