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231.
Theoretical and practical issues concerning the multi-faceted task of mitigating the latero-torsional seismic response of a prototypal frame structure with asymmetric mass distribution are approached.Chevron braces with embedded magnetorheological dampers acting on the interstory drift are used to ensure additional energy dissipation.The semi-active control strategy employed to govern the modifi cation of the damper characteristics via feedback is based on the selection of optimal forces according to a H2/L... 相似文献
232.
Salvatore Alparone Andrea Cannata Salvatore Gambino Stefano Gresta Vincenzo Milluzzo Placido Montalto 《Bulletin of Volcanology》2010,72(7):803-816
We investigated the relationship between volcano-seismic events, recorded at La Fossa crater of Vulcano (Aeolian Islands,
Italy) during 2004-2006, and the dynamics of the hydrothermal system. During the period of study, three episodes of increasing
numbers of volcano-seismic events took place at the same time as geothermal and geochemical anomalies were observed. These
geothermal and geochemical anomalies have been interpreted as resulting from an increasing deep magmatic component of the
hydrothermal fluids. Three classes of seismic events (long period, high frequency and monochromatic events), characterised
by different spectral content and various similarity of the waveforms, have been recognised. These events, clustered mainly
below La Fossa crater area at depths of 0.5–1.1 km b.s.l., were space-distributed according to the classes. Based on their
features, we can infer that such events at Vulcano are related to two different source mechanisms: (1) fracturing processes
of rocks and (2) resonance of cracks (or conduits) filled with hydrothermal fluid. In the light of these source mechanisms,
the increase in the number of events, at the same time as geochemical and geothermal anomalies were observed, was interpreted
as the result of an increasing magmatic component of the hydrothermal fluids, implying an increase of their flux. Indeed,
such variation caused an increase of both the pore pressure within the rocks of the volcanic system and the amount of ascending
fluids. Increased pore pressures gave rise to fracturing processes, while the increased fluid flux favoured resonance and
vibration processes in cracks and conduits. Finally, a gradual temporal variation of the waveform of the hybrid events (one
of the subclasses of long period events) was observed, likely caused by heating and drying of the hydrothermal system. 相似文献
233.
Ana Da Silva Vincenzo Costanzo-Álvarez Nuri Hurtado Milagrosa Aldana Germán Bayona Oswaldo Guzmán Diego López-Rodríguez 《Studia Geophysica et Geodaetica》2010,54(4):607-631
In this work we have assessed the hybrid algorithm of NeuroFuzzy logic (NFL), to establish a correlation between global climatic
changes (benthic foraminiferal δ18O data), experimental S-ratio (factor characterizing stability of remanent magnetization) and magnetic susceptibility (κ).
Magnetic proxies have been measured in 44 samples of the Colombian stratigraphic well Saltarín 1A (distal Llanos foreland
basin). κ and Sratios were linked to global δ18O data assuming a constant accumulation rate for a 305 meters thick stratigraphic interval flanked by the two palynological
age constrains available. This interval encompasses, from top to base, the bottom of the Guayabo formation, the León, and
the upper unit of the Carbonera formations (lower to middle Miocene). The best inference is accomplished applying a Takagi-Sugeno-Kan
(TSK) fuzzy model with four fuzzy rules and the δ18O, S-ratios and κ data used in a linear form to train the system. These results are interpreted as the outcome of a significant
influence of global climatic changes upon magnetic proxies. A stronger correlation is perhaps prevented by the likely influence
of local and regional tectonic events and climatic changes that could have affected the distal segment of the Colombian Llanos
foreland basin during Miocene times. We argue that late diagenesis of primary magnetic minerals and the assumption of a constant
accumulation rate might have a minor influence on these results. 相似文献
234.
The progressive bond breakage of artificially cemented sands induced by shear straining was investigated through conventional isotropically consolidated drained triaxial compression tests. Sand specimens were prepared with a low degree of cementation by adopting a chemical grout. Test results were interpreted in terms of two stress–dilatancy theories for cohesive-frictional materials proposed in literature. The influence of debonding on the stress–dilatancy behaviour of cemented sands was analysed with particular emphasis on the ‘delayed dilatancy’ phenomenon. A bonding degradation curve was determined for each test relating the interparticle cohesion (c) to the magnitude of the total plastic strain vector (εd) and a bond degradation rate factor (Dc) was assessed from each curve. The maximum value of interparticle cohesion (c0) before the onset of bond degradation under shearing was found to correspond with a sharp decrease in the soil stiffness of the specimens. The influence of the effective confining stress (p′c) on both c0 and Dc parameters gathered from each test was also ascertained. 相似文献
235.
Vincenzo Costanzo-Álvarez Rosa Devesa-Rey Milagrosa Aldana María Teresa Barral Diego López-Rodríguez Belkys Andrade 《Environmental Earth Sciences》2017,76(13):454
A study of surface sediments from the Anllóns riverbed (northwestern Spain) was conducted to assess the use of their magnetic properties as proxies of recent trace element contamination (i.e., As, Zn, Pb, Cr, Ni and Cu). Thermomagnetic curves, hysteresis parameters, specific magnetic susceptibility χ, frequency-dependent magnetic susceptibility κ FD%, magnetic remanence and saturation isothermal remanent magnetization ratios (i.e., S and SIRM/χ) reveal the presence of mostly fine-grained magnetite and maghemite in these samples. The Tomlinson Pollution Load Index (PLI), as well as the magnetic parameters χ, κ FD%, SIRM/χ and S-ratios, vary more or less in agreement to each other when they are sequentially arranged throughout a 30-km-long transect that goes from the town of Carballo to the river mouth in Ponteceso. From that profile, it is possible to identify an anomaly of χ that lies between two small peaks of the PLI and seems to define a contaminated area probably linked to a diffuse low-impact source of pollution. There is also a conspicuous peak of the PLI that is likely associated to a nearby gold mine. The variations of the κ FD%’s along the transect are the ones that best reflect the changes in the PLI values, regardless of the level of contamination. This result suggests that adsorption is the main mechanism of trace elements removal by Fe oxides in these samples. Direct signal analyses, used to decompose the isothermal remanent magnetization curves, reveal the presence of four magnetic fractions, with varying relative concentrations all over the profile, namely single-domain magnetite, close to the superparamagnetic threshold (SD/SP) and/or maghemite (\(\log B_{1/2}\) ca 1.2), single-domain magnetite (\(\log B_{1/2}\) ca 2), hematite (\(\log B_{1/2}\) ca 2.5) and goethite (\(\log B_{1/2}\) ca 3.5). Integrating all the available information, it was sketched out a likely sequence of events that included magnetic minerals neoformation in parent soils, their subsequent chemical transformations and the contamination episodes that affected the region. 相似文献
236.
Michele Punzo Giuseppe Cavuoto Daniela Tarallo Vincenzo Di Fiore 《Marine Geophysical Researches》2017,38(3):313-323
We present high-resolution Vp models of the Capo Granitola harbor, Sicily (Italy) obtained by first arrival traveltime tomography. Seismic data were collected along four hydrophone arrays on the sea-bottom and via a Watergun as seismic source, in order to plan dredging operations in the harbor. Using a hydrophone spacing of 2.5 m and shot spacing of 5 m, very high resolution quality data were recorded. Seismic tomography expands existing knowledge of the harbour subsoil with a penetration of about 20 m, illuminating the Lower Pleistocene bedrock (Marsala calcarenites) that corresponds to high-Vp regions (Vp?>?4.5 km/s). Low Vp (1.8–4.5 km/s) deposits belonging to terraced calcarenites (Upper Pleistocene in age) are also well imaged; they are about 8 m thick and lie below loose sand deposits (Vp?=?1.5 km/s). The substratum has an articulated morphology; Vp images unravel small steps in the basement probably related to structural discontinuities (e.g., faults). Processing data with 3D techniques enables images of the structure and the thickness of the lithotypes to be reconstructed, thus leading to large-scale, realistic estimates of the total quantity of material to be excavated or dredged. Tomographic profiles permit clear discrimination of the soft sediment above the basement and thus allow the determination of the total volume of sediment above the seismic bedrock, estimated at about 265,000 m3. 相似文献
237.
238.
Luciano?TelescaEmail author Marianna?Balasco Gerardo?Colangelo Vincenzo?Lapenna 《Natural Hazards》2005,34(2):177-198
In the present paper we analyse the series of extreme events in geoelectrical signals recorded at the monitoring station Tito located in a seismic area of southern Italy. Applying an objective criterion to estimate the probability of occurrence of extreme events in the time series (Cuomo et al., 1996; Cuomo et al., 1997), we found a correlation between the geoelectrical anomalies and earthquakes in the area monitored during the period of recording. 相似文献
239.
Alessandro Iannace Glauco Bonardi Marco D'Errico Stefano Mazzoli Vincenzo Perrone Stefano Vitale 《Comptes Rendus Geoscience》2005,337(16):373
A new structural–stratigraphic synthesis of the Apennine units of northern Calabria is presented. The Meso-Cenozoic successions are grouped into two tectonic units, named Pollino–Ciagola Unit (PCU) and Lungro–Verbicaro Unit (LVU), comprising terrains formerly attributed to five different tectonic units. FeMg carpholite and blue amphibole record HP–LT metamorphism in the LVU, followed by progressive decompression leading to final greenschist facies re-equilibration during dominantly extensional deformation. Final tectonic emplacement of the LVU over the PCU post-dated the metamorphism of the LVU and was accompanied by intense ductile deformation along zones of strain localisation in footwall rocks. All of the units were later affected by folding and minor thrusting during subsequent Apennine tectonics. To cite this article: A. Iannace et al., C. R. Geoscience 337 (2005). 相似文献
240.
Chloritized annite from the Irizar granite has been used for laser-heating experiments, following the procedures used for 40Ar–39Ar dating (heating steps in the 600–1080 °C temperature range). Four runs, at different temperatures, have been characterized using transmission electron microscopy, electron diffraction, micro-Raman and micro-IR spectroscopies. The water loss was evaluated by thermogravimetry. The chlorite domains break down first forming (001) amorphous layers, that later coalesce to rounded, equant inclusions and finally recrystallize to olivine and spinels plus silica glass. These phases occur within negative crystals hosted in ordered dehydrated annite, produced by dehydration and annealing of the starting annite. Dehydrated annite, olivine and spinels display topotactic relationships, determined by the common orientation of closely packed oxygen layers. 相似文献