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91.
Energy partitioning during seismic slip in pseudotachylyte-bearing faults (Gole Larghe Fault, Adamello, Italy) 总被引:1,自引:0,他引:1
Lidia Pittarello Giulio Di Toro Andrea Bizzarri Giorgio Pennacchioni Jafar Hadizadeh Massimo Cocco 《Earth and Planetary Science Letters》2008,269(1-2):131-139
The determination of the earthquake energy budget remains a challenging issue for Earth scientists, as understanding the partitioning of energy is a key towards the understanding the physics of earthquakes. Here we estimate the partition of the mechanical work density into heat and surface energy (energy required to create new fracture surface) during seismic slip on a location along a fault. Earthquake energy partitioning is determined from field and microstructural analyses of a fault segment decorated by pseudotachylyte (solidified friction-induced melt produced during seismic slip) exhumed from a depth of ~ 10 km—typical for earthquake hypocenters in the continental crust. Frictional heat per unit fault area estimated from the thickness of pseudotachylytes is ~ 27 MJ m− 2. Surface energy, estimated from microcrack density inside clast (i.e., cracked grains) entrapped in the pseudotachylyte and in the fault wall rock, ranges between 0.10 and 0.85 MJ m− 2. Our estimates for the studied fault segment suggest that ~ 97–99% of the energy was dissipated as heat during seismic slip. We conclude that at 10 km depth, less than 3% of the total mechanical work density is adsorbed as surface energy on the fault plane during earthquake rupture. 相似文献
92.
Marsh soil properties vary drastically across estuarine salinity gradients, which can affect soil strength and, consequently, marsh edge erodibility. Here, we quantify how marsh erosion differs between saline and brackish marshes of the Mississippi Delta. We analyzed long-term (1932–2015) maps of marsh loss and developed an algorithm to distinguish edge erosion from interior loss. We found that the edge erosion rate remains nearly constant at decadal timescales, whereas interior loss varies by more than 100%. On average, roughly half of marsh loss can be attributed to edge erosion, the other half to interior loss. Based on data from 42 cores, brackish marsh soils had a lower bulk density (0.17 vs. 0.27 g/cm3), a higher organic content (43% vs. 26%), a lower shear strength (2.0 vs. 2.5 kPa), and a lower shear strength in the root layer (13.8 vs. 20.7 kPa) than saline marsh soils. We then modified an existing marsh edge erosion model by including a salinity-dependent erodibility. By calibrating the erodibility with the observed retreat rates, we found that the brackish marsh is two to three times more erodible than the saline marshes. Overall, this model advances the ability to simulate estuarine systems as a whole, thus transcending the salinity boundaries often used in compartmentalized marsh models. 相似文献
93.
Giulio Castori Marco Corradi Alessandro De Maria Romina Sisti Antonio Borri 《Bulletin of Earthquake Engineering》2018,16(10):4561-4580
Studies oriented to restoration and conservation of historical monumental buildings have recourse to structural analysis as a way to investigate the genuine structural features of the construction, to better understand its present condition and actual causes of existing damage, to estimate its safety conditions and to determine necessary remedial measures. Based on this background, this paper discusses on the seismic vulnerability of masonry fortresses by means of an analysis methodology based on three different analytical procedures, according to an increased knowledge of the structure. As a relevant case study the Albornoz fortress, a 14th stone masonry construction located in central Italy, was selected. Initially, the strategy proposed to perform this task was aimed at testing and developing an expeditious and non-destructive procedure to evaluate both the seismic vulnerability and the main mechanical properties of the different masonry typologies. The macroscale structural behavior of the fortress was then evaluated through a nonlinear static analysis (pushover) and a more simple approach based on the kinematic theorems of the limit analysis. From this point of view, by comparing the capacity of the construction to withstand lateral loads with the expected demands resulting from seismic actions, these methods provided a highly effective means of verifying the safety of the masonry structure and its vulnerability to extensive damage and collapse. 相似文献
94.
YueFang Li Zhen Li Ju Huang Giulio Cozzi Clara Turett Carlo Barbante LongFei Xiong 《寒旱区科学》2017,9(6):568-579
Although previous investigations of the trace elements in snow and ice from the Qinghai-Tibetan Plateau obtained interesting information about pollution from human activities on the plateau, most were based on traditional acidification methods. To emphasize the influence of the different sample-preparation methods on the records of trace elements and rare earth elements, snow samples were collected from glaciers on the Qinghai-Tibetan Plateau in China and prepared using two methods: traditional acidification and total digestion. Concentrations of 18 trace elements (Al, Ti, Fe, Rb, Sr, Ba, V, Cr, Mn, Li, Cu, Co, Mo, Cs, Sb, Pb, Tl, and U), along with 14 rare earth elements (REEs: La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu), Y, and Th in the snow samples, were measured using inductively coupled plasma-sector field mass spectrometry (ICP-SFMS). The results showed that the mass fraction of the trace elements (defined as ratio of concentration in the acid-leachable fraction to that in the digested sample) such as Mo, Ti, Al, Rb, and V, varied from 0.06 to 0.5. The mass fraction of other trace elements varied from about 0.6 to more than 0.9; those of the REEs, Y, and Th varied from 0.34 to 0.75. Lower mass fractions will lead to an overestimated contribution of other sources, especially human activities, and the underestimated fluxes of these trace elements (especially REEs, Y, and Th, as well as dust) if the REEs are used as the proxy for the crust dust. The two sample-preparation methods exhibited different REE normalized distribution patterns, REE ratios, and provenance-tracing results. The REE normalized distribution patterns and proxies in the digested samples are more reliable and integrated than those found in traditional acidification method for dust-provenance tracing. 相似文献
95.
Micòl Mastrocicco Giulio Vignoli Nicolò Colombani Nasser Abu Zeid 《Environmental Earth Sciences》2010,61(2):311-322
A portion of an unconfined alluvial aquifer located in the Padana Plain (Italy) was characterized following an integrated
hydro-geophysical approach. Initially an electrical resistivity tomography (ERT) survey was employed to localize the boundaries
of a modest paleo-channel body and to design the installation of a groundwater monitoring network. Multilevel slug-tests were
performed to estimate the aquifer’s saturated hydraulic conductivities. Determined permeability values together with electrical
resistivity data were correlated. The correlation resulted in a site specific bi-logarithmic linear relationship. Based on
this relationship, punctually determined hydraulic conductivities were spatially extended over the studied flow domain. Finally,
continuously measured piezometric heads were used to calibrate a 3D flow model. Sensitivity analysis was performed to confirm
the reliability of the reconstructed permeability field, as well as, to assess the minimum number of direct measurements needed
to safely characterize the selected aquifer portion. The integration of the ERT survey results with the classical hydrogeological
tests can be conveniently applied to constrain the permeability field during flow model calibration. Although the applicability
of the determined relationship is site specific, the followed procedure is useful especially when there is a need to optimize
the available resources and in case of small-scale pilot studies. 相似文献
96.
Giulio Ottonello 《Geochimica et cosmochimica acta》2009,73(21):6447-6654
The hexa-aqua complexes [Fe(H2O)6−m−n(OH)n](2−n)+n = 0 → 3, m = 0 → 6 − n; [Fe(H2O)6−m−n(OH)n](3−n)+n = 0 → 4, m = 0 → 6 − n were investigated by ab-initio methods with the aim of determining their ground-state geometries, total energies and vibrational properties by treating their inner solvation shell as part of their gaseous precursor1 (or “hybrid approach”). After a gas-phase energy optimization within the Density Functional Theory (DFT), the molecules were surrounded by a dielectric representing the Reaction Field through an implicit Polarized Continuum Model (PCM). The exploration of several structural ligand arrangements allowed us to quantify the relative stabilities of the various ionic species and the role of the various forms of energy (solute-solvent electronic interaction, cavitation, dispersion, repulsion, liberation free energy) that contribute to stabilize the aqueous complexes. A comparison with experimental thermochemistries showed that ab-initio gas-phase + solvation energies are quite consistent with experimental evidence and allow the depiction of the most stable form in solution and the eventual configurational disorder of water/hydroxyl species around central cations. A vibrational analysis performed on the 54Fe, 56Fe, 57Fe and 58Fe isotopomers indicated important separative effects systematically affected by the extent of deprotonation. The role of the system’s redox state (fO2) and acidity (pH) on the isotopic imprinting of the aqueous species in solution was investigated by coupling the separative effects with speciation calculations. The observed systematics provided a tool of general utility in the interpretation of the iron isotopic signature of natural waters. Applications to the interpretation of isotopic fractionation in solution dictated by redox equilibria and to the significance of the Fe-isotopic imprinting of Banded Iron Formations are given. 相似文献
97.
Giulio Morteani Giovanni Ruggieri Peter Möller Christine Preinfalk 《Mineralium Deposita》2011,46(2):197-210
The CO2-rich geothermal fluids produced in the Piancastagnaio geothermal field (Mt. Amiata geothermal area, Southern Tuscany, Italy)
show temperatures up to 360°C and pressures of about 200 bar at depths of around 3,500 m (Giolito, Ph.D. thesis, Università
degli Studi di Firenze, Italy, pp 1–147, 2005). CaCO3- and/or SiO2-dominated scales are deposited in the pipes leading to the pressure and atmospheric separators of the geothermal wells. High
content of metastibnite and/or stibnite in both calcite and silica scales and Sb contents of up to 50 mg/L in the fluids indicate
their mineralising potential. The red or black colours of the scales depend on the predominance of red metastibnite or black
stibnite, respectively. In our condensation experiments, as well as during deposition of the scales, metastibnite is the first
Sb2S3 mineral to form. In a second stage, metastibnite is transformed to stibnite. During depressurization the Hg content of geothermal
fluids partitions preferentially into the gas phase, whereas Sb and As remain in the liquid phase. This separation explains
the often observed areal separation of Hg and Sb mineralization. The multistage deposition of Sb in the mining district of
Tuscany is due to a periodic restoration of the permeability of the ore-bearing faults by microseismic events and subsequent
host rock brecciation. The still ongoing microseismic events are induced by the accumulation of high-pressure CO2-rich fluids along faults followed by mechanical failure of the faults. 相似文献
98.
F. Cara G. Di Giulio G. P. Cavinato D. Famiani G. Milana 《Bulletin of Earthquake Engineering》2011,9(6):1961-1985
The Fucino basin (Central Italy) is one of the largest intramountain alluvial plain in the Apennines range. It has a tectonic
origin related to the presence of important systems of faults located in its northern and eastern edges. Some of these faults
are still active and capable of generating strong seismic events. Site effects related to the soft soils filling the basin
can be very important. In this paper we show the preliminary results of a seismic network installed in the Fucino area in
order to collect information about site amplification effects and geometry of the basin. We analyze ambient seismic vibrations
and recordings of about 150 local earthquakes mainly related to the seismic sequence of the April 6th 2009 Mw 6.3 L’Aquila
event. Moreover the strongest events of L’Aquila sequence were analyzed at the three permanent strong-motion stations operating
in the area. Using standard spectral techniques we investigate the variation of resonance frequencies within the basin. The
ground motion recorded in the Fucino plain is mainly characterized by strong energy at low-frequencies (f < 1 Hz) affecting both horizontal and vertical components. This is particularly evident for stations deployed in correspondence
of very thick deposits of sedimentary filling, where a significant increase of ground-motion amplitude and duration is likely
caused by locally generated surface waves. The amplification at low-frequencies (<1 Hz) on the horizontal components can reach
up a factor of 10 in comparison to nearby stiff sites. However, we found evidences of seismic amplification phenomena also
for stiff sites surrounding the basin, including stations of the Italian strong motion network. The independent geological
information and the shallow shear-velocity profiles available for the basin can be combined with resonance frequencies for
deriving representative geological sections to be used as base for future numerical 2D–3D modeling of the basin. 相似文献
99.
Claudio Arias Augusto Azzaroli Giulio Bigazzi Francescopaolo Bonadonna 《Quaternary Research》1980,13(1):65-74
Analysis of some sedimentary series near Rome and comparison with other series in northern and southern Italy give evidence that Arctica islandica, considered a marker species for the beginning of the Pleistocene, appears during the Re´union paleomagnetic event (about 2 my ago). A period of erosion, called the Aullan erosional phase, is evident in the lower part of the late Villafranchian (= early Pleistocene, Olivola faunal unit). 相似文献
100.
The continuing public concern with overfishing ignores the underlying problems that face fishery mangers. Attention needs to be given to (1) the transitory nature of the ocean environment, (2) the natural variation in fish stocks, (3) the role of the fishing industry and market forces in fishery management, and (4) the failure to focus on what it is we most need from the oceans, in what form we need it, and at what price. 相似文献