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761.
762.
In the present work, a precipitation and temperature series from Barcelona (Spain) are analysed in order to detect the possible existence of climatic changes or cycles. The analysis is carried out both from the temporal and spectral standpoints. The techniques used range from the classical periodogram and Blackman-Tukey method through to the Maximum Entropy method. The results do not show the existence of climatic cycles, though they do show a clear tendency toward increased precipitation and decreased temperature, since the last years of series. 相似文献
763.
Roberto Scandone Lisetta Giacomelli Paolo Gasparini 《Journal of Volcanology and Geothermal Research》1993,58(1-4)
Mount Vesuvius had eruptions ranging between VEI 5+ to 0–1 during the last 2000 years. Infrequent explosive eruptions are recorded during the period 79 AD to 1631. Since the violent explosive eruption of 1631, the volcano has been in persistent activity, rebuilding the morphology that it had before that eruption. A succession of explosive and effusive eruptions occurred until 1944, with a predominance of short and violent episodes until 1872 and longer effusive eruptions since that date. Two factors mainly controlled the character of volcanic activity during this period: (1) the strength of the cone, which allowed, in the earlier period, an easy fracturing, rapid drainage, and pressure release of the magma column; (2) the interaction between magma and water, which enhanced the explosivity of several eruptions.The volcano appears to have reached a stage of quiescence because it finally attained a shape of equilibrium in which the height of the mountain is sufficient to counterbalance the buoyancy of the magma. 相似文献
764.
Suárez Gerardo Espinosa-Aranda J. M. Cuéllar Armando Uribe Antonio Ibarrola Gerardo García Armando Islas Roberto Camarillo Lucio 《Natural Hazards》2021,108(3):3085-3098
Natural Hazards - The Mexican Seismic Alerting System (SASMEX) successfully alerted for the June 23, 2020, La Crucecita earthquake (Mw 7.4) in southern Mexico. The time between the alert broadcast... 相似文献
765.
Pepe Giacomo Cevasco Andrea Piazza Michele Macciò Roberto Arrighetti Fabio Casagli Nicola 《Landslides》2021,18(12):3799-3820
Landslides - This study presents the employment of automatic deep drainage systems to stabilize the Mendatica landslide, one of the largest relict landslides of western Liguria (north-western... 相似文献
766.
Geochemical Characterization of Magnetite and Geological Setting of the Iron Oxide ± Iron Silicate ± Iron Carbonate Rich Pb–Zn Sulfides from the La Unión and Mazarrón Stratabound Deposits (SE Spain)
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José Ángel López‐García Roberto Oyarzun Javier Lillo José Ignacio Manteca Paloma Cubas 《Resource Geology》2017,67(2):139-157
From a mineralogical point of view the La Unión ore field (SE Spain) can be regarded as an oddity as some of its hydrothermal, stratabound type deposits display an extremely unusual paragenesis comprising magnetite ± greenalite ± minnesotaite ± siderite and galena ± sphalerite (IOSC – LZS). Recent mineralogical studies have shown that this paragenesis is also present at the neighboring Mazarrón ore field. These ore fields share a similar geologic setting, involving metamorphic and sedimentary rocks (Paleozoic s.l. to Permian) hosting late Miocene high‐K calc‐alkaline volcanic and subvolcanic rocks. The latter have andesitic to dacitic composition, and triggered hydrothermal activity and ore deposition. This study discusses the detailed mineral chemistry of magnetite samples from Mazarrón and La Unión and provides some hints for the origin of the IOSC – LZS paragenesis. We performed electron microprobe (EPMA) analyses in magnetite samples from La Unión and Mazarrón to determine the contents of minor and trace elements (Zn, Ni, Mn, Cr, V, K, Ca, Ti, Al, Si, Mg). Given that some results fell below the detection limit for the EPMA instrumental conditions we used robust regression on order statistics (robust ROS), with the NADA package in R to deal with these data sets. The Ca + Al + Mn contents in magnetites from San Cristóbal and Emilia are equivalent to the mean contents of those of IOCG, Kiruna, BIF, Cu porphyry, skarn, VMS, hydrothermal and clastic Pb–Zn deposits, but they are low in Ti + V and Ni + Cr. The principal components analysis indicates that Zn, Ni, Cr, V, K, Ca, Ti, and Mg are roughly collinear, therefore correlated, being also independent from Fe. Besides, the function discriminant analysis of data shows that the magnetites from Emilia and San Cristóbal cluster in differentiated groups, thus probably reflecting some differences related to the distance to the magmatic source that triggered the hydrothermal system: proximal in the case of San Cristóbal and distal in Emilia. 相似文献
767.
Two families of passive seismic control devices exploiting the peculiar properties of shape memory alloy (SMA) kernel components have been implemented and tested within the MANSIDE project (Memory Alloys for New Seismic Isolation and Energy Dissipation Devices). They are special braces for framed structures and isolation devices for buildings and bridges. Their most important feature is their extreme versatility, i.e. the possibility to obtain a wide range of cyclic behaviour — from supplemental and fully re‐centring to highly dissipating — by simply varying the number and/or the characteristics of the SMA components. Other remarkable properties are their extraordinary fatigue resistance under large strain cycles and their great durability and reliability in the long run. In this paper, the working mechanisms of the SMA based devices are outlined and the experimental tests carried out to verify the above‐mentioned properties are extensively described. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
768.
Marialuce Bruscoli rea Ferrara Roberto Fabbri Benedetta Ciardi 《Monthly notices of the Royal Astronomical Society》2000,318(4):1068-1072
We calculate the secondary anisotropies in the cosmic microwave background (CMB) produced by inhomogeneous reionization from simulations in which the effects of radiative and stellar feedback effects on galaxy formation have been included. This allows us to determine self-consistently the beginning ( z i ≈30), the duration ( δz ≈20) and the (non-linear) evolution of the reionization process for a critical density cold dark matter (CDM) model. In addition, from the simulated spatial distribution of ionized regions, we are able to calculate the evolution of the two-point ionization correlation function, C χ , and obtain the power spectrum of the anisotropies, C ℓ , in the range 5000<ℓ<106 . The power spectrum has a broad maximum around ℓ≈30 000, where it reaches the value 2×10−12 . We also show that the ionization correlation function C χ is not Gaussian, but at separation angles θ ≲10−4 rad it can be approximated by a modified Lorentzian shape; at larger separations an anticorrelation signal is predicted for both C χ and C ( θ ). Detection of signals as above will be possible with future millimetre-wavelength interferometers like the Atacama Large Millimeter Array (ALMA) , which appears as an optimum instrument to search for signatures of inhomogeneous reionization. 相似文献
769.
Magma chamber evolution prior to the Campanian Ignimbrite and Neapolitan Yellow Tuff eruptions (Campi Flegrei,Italy) 总被引:2,自引:0,他引:2
The Campi Flegrei (Campanian Region, Italy) experienced two cataclysmic caldera-forming eruptions which produced the Campanian
Ignimbrite (39 ka, CI) and the Neapolitan Yellow Tuff (15 ka, NYT). We studied the minor eruptions before both these large
events to understand magma chamber evolution leading towards such catastrophic eruptions. Major, trace element, and Sr and
Nd isotope compositions of pre-Campanian Ignimbrite and pre-Neapolitan Yellow Tuff products define distinct geochemical groups,
which are here interpreted as distinct magma batches. These batches do not show any transitional trend towards the CI and
NYT eruptions. The CI and NYT systems are decoupled geochemically and isotopically. At least one of the pre-CI and one of
the pre-NYT erupted magma batches qualifies as mixing endmembers for the large CI and NYT eruptions, and thus, must have been
stored in reservoirs for some time to remain available for the CI and NYT eruptions. The least evolved, isotopically distinct
magma compositions that are typical of the last phases of the NYT and CI eruptions did not occur before caldera-forming events.
Based on the new data, we propose the following scenario: Multiple magma chambers with distinct compositions existed below
the Campi Flegrei before the CI and NYT eruptions and remained generally separated for some time unless new magma was recharged.
In each case, one of the residing magma reservoirs was recharged by a new large-volume magma input of intermediate composition
from a deeper differentiating magma reservoir. This may have triggered the coalescence of the previously separated reservoirs
into one large chamber which fed the cataclysmic caldera-forming eruption. Large magma chambers in the Campi Flegrei may therefore
be ephemeral features, interrupted by periods of evolution in individual, separated magma reservoirs. 相似文献
770.
Roberto Sulpizio Elena Zanella José Luis Macías 《Journal of Volcanology and Geothermal Research》2008
Thermal remanent magnetization (TRM) analyses were carried out on lithic fragments from two different typologies of pyroclastic density current (PDC) deposits of the 1982 eruption of El Chichón volcano, in order to estimate their equilibrium temperature (Tdep) after deposition. The estimated Tdep range is 360–400 °C, which overlaps the direct measurements of temperature carried out four days after the eruption on the PDC deposits. This overlap demonstrates the reliability of the TRM method to estimate the Tdep of pyroclastic deposits and to approximate their depositional temperature. These results also constraint the time needed for reaching thermal equilibrium within four days for the studied PDC deposits, in agreement with predictions of theoretical models. 相似文献