A new code has been used to simulate the formation of elliptical galaxies via a dissipationless collapse by a numerical experiment. Preliminary results of numerical simulations are presented for initial 2T/|W| conditions ranging from 10–2 to 10–5. The importance of inhomogeneity in the initial density distribution and of merging is outlined.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain. 相似文献
Summary The surface thermal flux of the continental margins of the northwestern Mediterranean Sea is interpreted on the basis of a 1-D instantaneous pure shear stretching model of the lithosphere in terms of three components: the background heat flowing out from the asthenosphere (38 mW m–2), the transient contribution depending on the rift age and extension amount (35 mW m–2 at the most), and the contribution due to the radiogenic elements of the lithosphere. The radiogenic component is estimated at the continental margins of the Ligurian-Provençal basin and Valencia trough, and in the surrounding mainland areas by means of available data of surface heat generation from Variscan Corsica, Maures-Estérel and the Central Massif along with a geophysical-petrological relationship between heat production and seismic velocity. The lithosphere radiogenic heat contribution ql decreases with the thinning factor according to the exponential law: ql() = a exp(-b), in which factor b is greater for that part of the lithosphere below the uppermost 10 km. Considering also the heat generated by radioactive isotopes in sediments, the stable Variscan lithosphere produces an average thermal flux of 30 mW m–2 which decreases by about one half where the lithosphere is thinned by one third. Although the surface heat generation is 2·1 – 3·3 µW m–3 in the Maures-Estérel massif — excepting small outcrops of dioritic rocks with lower heat production — and 1·8 µW m–3 for most of Corsica, the radiogenic heating within the lithosphere for such areas is nearly the same and does not explain the higher heat flux of the Corsica margin. This asymmetric thermal pattern with surface heat flux which is 10 – 15 mW m–2 higher than predictions is probably of upper mantle origin, or can be ascribed to penetrative magmatism. 相似文献
Two recent phases of mobilization of a large, rainfall-induced debris slide are analysed in terms of relationships between
rains and phases of displacement. The first activation at San Rocco (San Benedetto Ullano, Calabria) occurred on 28 January
2009, after extraordinary rains had stricken the region for a couple of months. Detailed geomorphologic field surveys, combined
with measurements of superficial displacements at datum points, were performed to properly recognize the evolution of the
phenomenon. In addition, a real-time control system of rains and superficial displacements measured at extensometers was implemented,
to better analyse the evolution of the phenomenon. In early May 2009, the activity reduced to very slow displacements, persisting
in the same condition for the following 8 months. On 1 February 2010, premonitory signs of a new phase of activation were
noticed, again following 2 months of extraordinary rainfalls. After few days of further precipitations, the middle sector
of the landslide activated since 11 February, disrupting the road network and threatening the major lifelines and some buildings.
A hydrological analysis aimed at simulating the dates of activation and the main phases of acceleration of the phenomenon
was carried out, by calibrating the empirical model FLaIR against the daily rainfalls and the history of known phases of mobilization since 1970. Calibration allowed to successfully
simulate both the cited phases of activity of the San Rocco landslide, by predicting the beginning of the movements as well
as the following paroxysmal stages, as testified by the measurements at datum points and extensometers. The set of parameters
obtained through calibration reflects the influence of both prolonged antecedent rains, and of high-intensity rainfalls of
shorter duration, which slightly preceded the major displacements. Once calibrated the model, a suitable threshold could be
defined, by analysing the trend of the mobility function against the history of activations of the considered slope movement,
and by excluding false alarms. Accordingly, a reliable tool for predicting the phases of activity of a large slope movement
could therefore be obtained. 相似文献
Particle acceleration at non-relativistic shocks can be very efficient, leading to the appearance of non-linear effects due to the dynamical reaction of the accelerated particles on the shock structure and to the non-linear amplification of the magnetic field in the shock vicinity. The value of the maximum momentum, p max, in these circumstances cannot be estimated using the classical results obtained within the framework of test-particle approaches. We provide here the first attempt at estimating p max in the cosmic ray modified regime, taking into account the non-linear effects mentioned above. 相似文献
The thickness of the seismogenic layer is a key parameter for seismic hazard, since it can be used to constrain the maximum depth of faulting and the potential magnitude. In this study, we compute the seismogenic thickness in the Italian region by defining the lower seismicity cut‐off, using high‐quality hypocentral locations of earthquakes that occurred in the past decade. Along the eastern Alps, the seismogenic thickness is about 12–14 km, laterally homogeneous along the entire south‐verging thrust front. In the Apennines extensional belt, lateral changes in seismogenic thickness are evident, and correlate with changes in the seismic energy released by past earthquakes. The potential magnitude is larger in the southern Apennines where the seismogenic thickness is greater (16–18 km) than in the northern Apennines where it is less (6–10 km) and seismic energy is partially released by the creeping of faults. 相似文献
A new dataset of first P-wave arrival times is used to derive the 3D tomographic model of the Campania-Lucania region in the
southern Apennines (Italy). We address the issue related to the non-uniqueness of the tomographic inversion solution through
massive numerical experimentation based on the global exploration of the model parameter space starting from a large variety
of physically plausible initial models. The average of all the realizations is adopted as the best-fit solution and the uncertainty
of the model parameters is studied using a statistical approach based on a Monte Carlo-type analysis. How the uncertainty
in the initial model, earthquake locations, and data influences the inversion result is studied by considering separately
the individual effects. Checkerboard tests are performed to estimate the resolving power of the dataset. Re-located seismicity
in a reliable new 3D tomographic model allows us to correlate the earthquake distribution with the main seismogenic structures
present in the area. 相似文献
The connection between thermal field and mechanical properties is analysed in the northern central Mediterranean region, extending from the Ligurian-Provençal basin to the Adriatic foredeep. As the thermal regime is still far from equilibrium in most of the tectonic units, transient thermal models are used. The temperature-depth distribution is estimated in four areas affected by the volcanic activity, which from the Neogene to the Present shifted from Corsica to the Apenninic arc. In the Adriatic foredeep, the thermal effects of the recent thrust-faulting phase in the buried sectors of the northern Apennines are taken into account.
The general context consists of convergence involving westward subduction of the Adriatic plate. This process caused anti-clockwise rotation of Corsica and Sardinia, which led to formation of the Ligurian marginal basin, and also resulted in crustal doubling and overthrusting in the northern Apennines and rifting in the northern Tyrrhenian.
Seismic activity is focused in the internal and external zones of the Apenninic arc, where low surface heat flux is observed, and in the western margin of the Ligurian-Provençal basin. This is a consequence not only of lateral variations in the thermal field but also of the different tectonic settings. Regional extensional patterns in the shallow crust, with minimum principal stress axes trending N60°E and E-W, are observed in the northern and in the southern sectors of the Apenninic arc, respectively. A compressional regime at depths greater than 30 km is observed below the northern sector of the arc, while to the south a change in the structure of the lithosphere is marked by a decrease in deeper seismic activity. Thrust faults and strike-slip faults with a thrust component support a compressional regime along the western margin of the Ligurian basin with maximum principal stress axis oriented N120°E.
Two lithospheric cross-sections across the study region are constructed, based on structural, thermal, gravity, rheological and seismic data. There is clear evidence of the presence of the subducting slab of the Adriatic plate, corresponding to a thickening of the uppermost brittle layer. The crustal seismicity cut-off corresponds to temperatures of 320–390°C. A brittle layer of considerable thickness is present in the uppermost mantle beneath Variscan Corsica and the Adriatic foredeep, with estimated seismic cut-off temperature of about 550 ± 50°C. 相似文献
Mathematical Geosciences - Recent advances in satellite technologies, statistical and mathematical models, and computational resources have paved the way for operational use of satellite data in... 相似文献