4,660 research outputs found
Progressive approach to eruption at Campi Flegrei caldera in southern Italy
Unrest at large calderas rarely ends in eruption, encouraging vulnerable communities to perceive emergency warnings of volcanic activity as false alarms. A classic example is the Campi Flegrei caldera in southern Italy, where three episodes of major uplift since 1950 have raised its central district by about 3 m without an eruption. Individual episodes have conventionally been treated as independent events, so that only data from an ongoing episode are considered pertinent to evaluating eruptive potential. An implicit assumption is that the crust relaxes accumulated stress after each episode. Here we apply a new model of elastic-brittle failure to test the alternative view that successive episodes promote a long-term accumulation of stress in the crust. The results provide the first quantitative evidence that Campi Flegrei is evolving towards conditions more favourable to eruption and identify field tests for predictions on how the caldera will behave during future unrest
Historical eartquakes at Ischia island and seismic hazard assessment
Hystorical data of seismicity at Ischia island (Southern Italy) cover a period of almost
800 years. Since 1228 numerous events exceeded VII MCS degree. The epicentral
areas of the earthquakes are located in the northern sector of the island; only one
earthquake (1302, VIII MCS degree) was correlated with the latter eruption occurred
during 1301-02 AD along the eastern sector of the island. In few cases the earthquakes
(1228, 1863, 1881, 1883 AD) were followed by landslides which have produces serious
damage while, in average, ground effects (i.e. fractures, capacity and temperature
variation of hot springs) were often observed before and after each event. The historical
seismicity of Ischia shows the peculiar characteristics of volcanic earthquakes
as shallow ipocentral depth ( 1 km), high intensity, strong directional attenuation
of effects and local amplification of damages. At Ischia, the 1883 AD earthquake of
“Casamicciola” represents the unique example of modern age earthquake in Mediterranean
volcanic area which produced more than 2300 fatalities. The catastrophic effects
of this earthquake (Imax=XI MCS degree) covered an area of about 3 km2 in
the northern sector of the island, while strong attenuation effects were observed, especially
along the south and east directions. From 1883 AD until today a seismic silence
in the island has been observed. Some events have been felt from the beginning of the
20th century while, in the last 10 years just few events (M < 2), have been recorded
by the INGV-OV surveillance seismic network, localized prevalently in the northern
sector of the island. The lack of significant seismicity allow the study of macroseimic
data of 1883 earthquake as the fundament issue for hazard assessment, also if considering
the increasing of housing density and the high exposed value in the island. Data
of earthquake damages and ground effects, obtained by archives sources and literature,
have been utilized (also using GIS cross-correlation with geological data) in order to
evaluate the tendency of the attenuation for different zones of the island, to detach the contribution of the source from the medium, and define the zones of maximum expected damage
On the mechanics of caldera resurgence of Ischia Island (southern Italy)
A model of caldera resurgence was applied to the Island of Ischia to explain uplift,
volcanic activity and tectonics on Mount Epomeo, as well as historical seismicity and slow
ground movements recorded for the past 2000 years. A two-dimensional mechanical model
was utilized for the crust, which was considered to be an elastic plate overlying a laccolith.
Geometric dimensions and mechanical parameters were constrained using geological,
geophysical and geochemical data.
We propose that a laccolith, with a diameter L of c. 10 km, and a depth of up to 1 km in the
centre of the island, triggered the caldera resurgence after the Mount Epomeo Green Tuff
eruption forming the caldera (55 000 a BP). A bending phase and a punched laccolith phase are
thought to have caused the observed deformations in the caldera. These processes control the
tectonics at the boundary of the Mount Epomeo resurgent structure, volcanic activity and
dynamics of the island
bending damages in galvanized ductile cast irons
Abstract Ductile cast irons (DCIs) are characterized by mechanical properties close to low and medium carbon steels. Carbon atoms are mainly localized in graphite nodules, which are dispersed in a metallic matrix. The microstructure of metallic matrix can be ferritic, austenitic, pearlitic, martensitic or their mix, depending on chemical composition and heat treatment. Thanks to the high castability and low production costs, DCIs are used in many fields (e.g., automotive and pipes). The wide utilization of DCIs in many fields and critical application leads to particular attention to the corrosion phenomenon. Hot dip galvanizing is one of most important protection process, used to protect metallic materials (mainly steels) against corrosion in many aggressive environments. In this work, a ferritic-pearlitic DCI (GS500) was galvanized by using a pure Zn bath at 440°C to generate a zinc coating. Bending tests on galvanized specimen were performed to generate crack damage in the coating phases. The bending cracks path propagation in zinc coatings were observed using both a light optical microscope and scanning electron microscope. A damage parameter, defined as a number of radial crack for a millimeter of the deformed arc, was evaluated for each zinc coating intermetallic phases
grain size influence on fatigue behaviour in a cuznal pe sma
Abstract Due to their capability to recover the initial shape, Shape Memory Alloys (SMAs) are widely used in many applications. Different grades are commercially available and they can be classified considering either their chemical compositions (Cu based, Ni based, Fe based and so on..) or according to their mechanical behaviour. The most used SMAs are the Ni based alloys thanks to their performances both in terms of mechanical resistance and in terms of fatigue resistance, but their costs are quite high. Cu based alloys are good competitors of the Ni based alloys. The recent optimization of their chemical composition improved both the corrosion resistance in aggressive environments and their mechanical performances. In this work, the influence of the grain size on fatigue crack propagation in two Cu-Zn-Al SMAs focusing on the damaging micromechanisms
Nonlinear convective motion of the asthenosphere and the lithosphere melting: a model for the birth of a volcano
The processes of heat transfer occurring between the Earth's asthenosphere and lithosphere are responsible for partial melting of rocks, leading to the magma generation and its migration and segregation in the crust and, possibly, to volcanoes generation at the surface. Convection is the dominant mechanism regulating the heat transfer from the asthenosphere to the lithosphere, although many aspects of the whole process are not yet clear. Therefore, the knowledge of the physical processes leading to the melting of the lithospheric rocks has important consequences in understanding the interior Earth dynamics, the surface volcanic dynamics, and its related hazards. Rock melting occurs when the temperature gradient meets the rock solidus. Here, we propose a nonlinear convective 1D analytical model (representing an approximation of more 3D complex models). The steady-state solution of our equation is in good agreement with the estimated geotherms of the asthenosphere. A perturbative approach leads to a heat swelling at the boundary between asthenosphere and lithosphere able to determine its melting and the birth of a volcano
Vacuum Structure and Flavor Symmetry Breaking in Supersymmetric SO(n_c) Gauge Theories
We determine the vacuum structure and phases of N=1 theories obtained via a
mass \mu for the adjoint chiral superfield in N=2, SO(n_c) SQCD. For large
number of flavors these theories have two groups of vacua. The first exhibits
dynamical breaking of flavor symmetry \USp(2n_f) \to U(n_f) and arises as a
relevant deformation of a non-trivial superconformal theory. These are in the
confined phase. The second group, in an IR-free phase with unbroken flavor
symmetry, is produced from a Coulomb branch singularity with Seiberg's dual
gauge symmetry. In the large-\mu regime both groups of vacua are well-described
by dual quarks and mesons, and dynamical symmetry breaking in the first group
occurs via meson condensation. We follow the description of these vacua from
weak to strong coupling and demonstrate a nontrivial agreement between the
phases and the number of vacua in the two regimes. We construct the
semiclassical monopole flavor multiplets and argue that their multiplicity is
consistent with the number of N=1 vacua.Comment: 67 pages, harvmac; Typos corrected, section 4.1 reworde
Resurgence and flank failure of Mt. Epomeo, Ischia Island (Southern Italy)
Risorgenza e collasso laterale del Monte Epomeo, Isola
d’Ischia
Il Monte Epomeo (787 m a.s.l.), ubicato nel settore centrale dell’isola
d’Ischia, mostra lo smantellamento del settore meridionale, depositi
di debris e franamenti diffusi che testimoniano la natura instabile
del monte. A seguito dell’eruzione ignimbritica del Tufo Verde
dell’Epomeo (55.000 anni), che genera una struttura calderica (10x7
km2), inizia la risorgenza della caldera fino alla formazione del Monte
Epomeo. Il sollevamento, generato dall’intrusione di un laccolite fino
a circa 1 km di profonditĂ , avrebbe determinato una forte instabilitĂ
gravitativa del blocco risorgente e prodotto uno o piĂą collassi laterali.
Questi hanno lasciato una struttura a ferro di cavallo, tipica di
processi da “avalancing”, aperta verso sud, e depositi con topografia
“hummocky” estesi a sud dell’Epomeo e rilevati recentemente da esplorazioni
sul fondo marino. Il processo che ha generato il collasso
e la formazione di un avalanche caldera è stato esaminato attraverso
l’analisi della dinamica e dei caratteri geologici, geomorfologici e
strutturali dell’area. Attualmente l’isola è caratterizzata da una fase di
stasi della risorgenza testimoniata da una condizione di moderata stabilitĂ
dei versanti dell’Epomeo. Quanto osservato indicherebbe una
bassa dinamica endogena nell’isola
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