A probabilistic approach for the classification of earthquakes as ��triggered�� or ��not triggered��     

Luigi Passarelli  Francesco Maccaferri  Eleonora Rivalta  Torsten Dahm  Elias Abebe Boku 《Journal of Seismology》2013,17(1):165-187

The occurrence time of earthquakes can be anticipated or delayed by external phenomena that induce strain energy changes on the faults. ??Anticipated?? earthquakes are generally called ??triggered??; however, it can be controversial to label a specific earthquake as such, mostly because of the stochastic nature of earthquake occurrence and of the large uncertainties usually associated to stress modelling. Here we introduce a combined statistical and physical approach to quantify the probability that a given earthquake was triggered by a given stress-inducing phenomenon. As an example, we consider an earthquake that was likely triggered by a natural event: the M?=?6.2 13 Jan 1976 Kópasker earthquake on the Grímsey lineament (Tj?rnes Fracture Zone, Iceland), which occurred about 3?weeks after a large dike injection in the nearby Krafla fissure swarm. By using Coulomb stress calculations and the rate-and-state earthquake nucleation theory, we calculate the likelihood of the earthquake in a scenario that contains only the tectonic background and excludes the dike and in a scenario that includes the dike but excludes the background. Applying the Bayes?? theorem, we obtain that the probability that the earthquake was indeed triggered by the dike, rather than purely due to the accumulation of tectonic strain, is about 60 to 90?%. This methodology allows us to assign quantitative probabilities to different scenarios and can help in classifying earthquakes as triggered or not triggered by natural or human-induced changes of stress in the crust.  相似文献   

Becoming a creative city: perspectives from Augustus’ Rome     

Eleonora Redaelli 《Urban geography》2013,34(4):608-623

The creative city discourse has been shaping cultural policy worldwide. Among the multifaceted goals highlighted by scholars, one aspect that is not thoroughly emphasized is the understanding of creative cities in terms of culture-centric approaches to foster city cohesion. In this paper, I study the value of focusing the idea of the creative city to integrate diverse communities in a historic context: the city of Rome during the reign of Augustus. The aim is to provide a broader historic frame of reference to better articulate the function of the creative city discourse. Through the analysis of primary and secondary literature in Ancient Studies, I highlight three aspects of Augustus’ remaking of Rome: integration, spectacles, and beauty. From these aspects, what emerges is the idea of a creative city as a vital and spectacular place that offers access to arts and culture involving the diversity of the population, presenting a wide range of art forms, and enhancing the beauty of the built space.  相似文献   

Volcanic and structural evolution of Pico do Fogo,Cape Verde          下载免费PDF全文

Juan‐Carlos Carracedo  Francisco J. Perez‐Torrado  Alejandro Rodriguez‐Gonzalez  Raphaël Paris  Valentin R. Troll  Abigail K. Barker 《Geology Today》2015,31(4):146-152

In recent months the media have drawn attention to the Cape Verde archipelago, with particular focus on the island of Fogo, the only island presently active and with an eruption that began on 23 November 2014, finally ceasing on 7 February 2015. The Monte Amarelo conical shield forms most of the 476 km² almost circular island of Fogo. After attaining a critical elevation of about 3500 m, the Monte Amarelo shield volcano was decapitated by a giant landslide that formed a caldera‐like depression (Cha das Caldeiras), which was subsequently partially filled by basaltic nested volcanism. This younger eruptive activity culminated in the construction of the 2829 m‐high Pico do Fogo stratocone, apparently entirely made of layers of basaltic lapilli. Continued growth of the Pico do Fogo summit eruptions was interrupted in 1750, most likely after the stratocone reached a critical height. Since then, at least eight eruptions have taken place inside the landslide depression at the periphery of the Pico do Fogo cone, including the 2014–2015 eruptive event. Strong geological similarities with the Canary Islands, 1400 km to the north, have been frequently noted, probably as a consequence of a common process of origin and evolution associated with a mantle hot‐spot. These similarities are particularly evident when comparing Fogo with the Teide Volcanic Complex on Tenerife, where a lateral collapse of the Las Cañadas stratovolcano also formed a large depression (the Caldera de Las Cañadas), now partially filled with the 3718 m‐high Teide stratocone. However, important geological differences also exist and probably relate to the contrasting evolutionary stages of both islands. The Las Cañadas volcano on Tenerife formed at a late post‐erosional stage, with predominantly evolved (trachyte and phonolite) magmas, while at Fogo basaltic volcanism is still dominant.  相似文献   

MC‐ICP‐MS Isotope Measurements with Direct Injection Nebulisation (d‐DIHEN): Optimisation and Application to Boron in Seawater and Carbonate Samples     

Pascale Louvat  Julien Bouchez  Guillaume Paris 《Geostandards and Geoanalytical Research》2011,35(1):75-88

We report here an optimisation of the demountable direct injection high efficiency nebuliser (d‐DIHEN) for isotopic measurements with a Neptune (ThermoFisher Scientific, Bremen, Germany) multi‐collector inductively coupled plasma‐mass spectrometer (MC‐ICP‐MS) and describe a method for boron isotopic ratio determination. With direct injection nebulisation 100% of the analyte was introduced into the ICP‐MS plasma and wash times were drastically reduced for elements such as boron and thorium. Compared to the classical stable introduction system (SIS: double Scott/cyclonic spray chamber), sensitivity for boron was 2–5 times higher with d‐DIHEN and wash times up to ten times shorter. Repeatability of ¹¹B/¹⁰B sample‐calibrator bracketing measurements reached 0.25‰ (2s) for seawater and coral samples. Method accuracy and reproducibility were tested on mixed reference solutions having δ¹¹B values in the ranges ?90 to +40‰ and ?2 to +2.5‰, demonstrating our ability to distinguish δ¹¹B values with differences of only 0.25‰. The international seawater reference material NRCC NASS‐5 (National Research Council, Ottawa, Canada), analysed in different sessions over a 10‐month period, yielded an average δ¹¹B value of +39.89 ± 0.25‰, in the upper range of previously published seawater values. A comparison between δ¹¹B determined by d‐DIHEN MC‐ICP‐MS and positive‐TIMS (P‐TIMS) for four modern corals showed an excellent agreement (with bias of less than 0.4‰).  相似文献   

Unraveling the hidden origin and migration of plagioclase phenocrysts by in situ Sr isotopes: the case of final dome activity at Nisyros volcano,Greece     

Eleonora?BraschiEmail author  Lorella?Francalanci  Simone?Tommasini  George?E.?Vougioukalakis 《Contributions to Mineralogy and Petrology》2014,167(3):988

This contribution reports a detailed study on in situ Sr isotope analyses, along with textural and compositional characteristics, of plagioclase phenocrysts occurring in the rhyodacitic dome-lavas and associated mafic enclaves, erupted during the last magmatic activity at Nisyros volcano (Greece). Dome-lavas and enclaves have a paragenesis dominated by plagioclase. We recognize five different types of plagioclase based on their specific textures and composition. Dome-lava plagioclases (Type-1) are mainly large (1–5 mm), subhedral, clear, and poorly zoned crystals with low An content (An_25–35). The plagioclase phenocrysts (Type-4 and Type-5) and groundmass microlites crystallizing in the enclaves, and found in dome-lavas as xenocrysts, have high An content (An_75–95). In both dome-lavas and enclaves, two other types of plagioclase do also occur: (1) plagioclase phenocrysts with size and core composition similar to those of Type-1 having a dusty sieve zone (DSZ) at the rims (Type-2); (2) plagioclases with a DSZ affecting the entire crystal but a thin rim (Type-3). The drilled plagioclases have ⁸⁷Sr/⁸⁶Sr negatively correlated with their An content. Low An cores of Type-1 and Type-2 have quite homogeneous ⁸⁷Sr/⁸⁶Sr (0.7044–0.7046), whose values are more radiogenic than their host magmas (0.70403–0.70408) and similar to those of the previous Upper Pumice (UP) rhyolite magma (0.70438–0.70456). The DSZs of Type-2 and Type-3 show lower and scattered ⁸⁷Sr/⁸⁶Sr (0.70397–0.70426) with intermediate and variable An content. High An cores of Type-4 and Type-5 have the least radiogenic Sr isotope composition (0.70379) in equilibrium with that measured in the enclaves (0.70384–0.70389). We demonstrate that Type-1 plagioclase crystallizes in the previous UP rhyolitic magmas representing the silica-rich magma from which the dome-lava melts derived by open system evolutionary processes (e.g., mixing, mingling, and crystal migration), caused by successive refilling of mafic enclave-forming magma. The Type-2 plagioclase derives from entrainment of Type-1 into the still molten enclave magma. The DSZs originated in response to the interaction between the low An plagioclase and the enclave mafic melt in which dissolution and re-crystallization acted together as function of the interaction time. Type-1 and Type-2 plagioclases record, therefore, a long-lived timescale of events starting from their crystallization in the UP rhyolite. Instead, the different width of DSZs (Type-2 and Type-3) seems to indicate short different interaction timescales between the single crystals and the enclave melt (from few hours to some 40 days). These microanalytical data contribute to the understanding of the origin of the rhyodacitic dome-lavas at Nisyros volcano and to set robust constraints on the dynamics of mingling/mixing processes in terms of crystal exchange pathways and enclave disaggregation.  相似文献   

Olivine or impact melt: Nature of the “Orange” material on Vesta from Dawn     

Lucille Le Corre  Vishnu Reddy  Nico Schmedemann  Kris J. Becker  David P. O’Brien  Naoyuki Yamashita  Patrick N. Peplowski  Thomas H. Prettyman  Jian-Yang Li  Edward A. Cloutis  Brett W. Denevi  Thomas Kneissl  Eric Palmer  Robert W. Gaskell  Andreas Nathues  Michael J. Gaffey  David W. Mittlefehldt  William B. Garry  Holger Sierks  Christopher T. Russell  Carol A. Raymond  Maria C. De Sanctis  Eleonora Ammanito 《Icarus》2013

NASA’s Dawn mission observed a great variety of colored terrains on asteroid (4) Vesta during its survey with the Framing Camera (FC). Here we present a detailed study of the orange material on Vesta, which was first observed in color ratio images obtained by the FC and presents a red spectral slope. The orange material deposits can be classified into three types: (a) diffuse ejecta deposited by recent medium-size impact craters (such as Oppia), (b) lobate patches with well-defined edges (nicknamed “pumpkin patches”), and (c) ejecta rays from fresh-looking impact craters. The location of the orange diffuse ejecta from Oppia corresponds to the olivine spot nicknamed “Leslie feature” first identified by Gaffey (Gaffey, M.J. [1997]. Icarus 127, 130–157) from ground-based spectral observations. The distribution of the orange material in the FC mosaic is concentrated on the equatorial region and almost exclusively outside the Rheasilvia basin. Our in-depth analysis of the composition of this material uses complementary observations from FC, the visible and infrared spectrometer (VIR), and the Gamma Ray and Neutron Detector (GRaND). Several possible options for the composition of the orange material are investigated including, cumulate eucrite layer exposed during impact, metal delivered by impactor, olivine–orthopyroxene mixture and impact melt. Based on our analysis, the orange material on Vesta is unlikely to be metal or olivine (originally proposed by Gaffey (Gaffey, M.J. [1997]. Icarus 127, 130–157)). Analysis of the elemental composition of Oppia ejecta blanket with GRaND suggests that its orange material has ∼25% cumulate eucrite component in a howarditic mixture, whereas two other craters with orange material in their ejecta, Octavia and Arruntia, show no sign of cumulate eucrites. Morphology and topography of the orange material in Oppia and Octavia ejecta and orange patches suggests an impact melt origin. A majority of the orange patches appear to be related to the formation of the Rheasilvia basin. Combining the interpretations from the topography, geomorphology, color and spectral parameters, and elemental abundances, the most probable analog for the orange material on Vesta is impact melt.  相似文献   

Iron oxidation state in impact glass from the K/T boundary at Beloc,Haiti, by high‐resolution XANES spectroscopy     

Gabriele Giuli  Sigrid Griet Eeckhout  Eleonora Paris  Christian Koeberl  Giovanni Pratesi 《Meteoritics & planetary science》2005,40(11):1575-1580

Abstract— We examined the local iron environment in nine impact glasses from the Cretaceous‐Tertiary (K/T) boundary section at Beloc, Haiti, which formed as the result of impact melting during the Chicxulub impact event. The samples have been analyzed by Fe K‐edge high‐resolution X‐ray absorption near edge structure (XANES) spectroscopy to obtain data on both the Fe oxidation state and the coordination number. The pre‐edge peak of our high‐resolution XANES spectra display noticeable variations indicative of significant changes in the Fe oxidation state spanning a wide range from about 20 to 75 mol% trivalent Fe. All data plot along the same trend, falling between two mixing lines joining a point calculated as the mean of a group of tektites studied so far (consisting of four‐ and five‐coordinated Fe²⁺) to ^[4]Fe³⁺ and ^[5]Fe³⁺, respectively. Thus, the XANES spectra can be interpreted as a mixture of ^[4]Fe²⁺, ^[5]Fe²⁺, ^[4]Fe³⁺, and ^[5]Fe³⁺. There is no evidence for six‐fold coordinated Fe; however, its presence in small amounts cannot be excluded from XANES data alone. Our observations can be explained by two possible scenarios: either these impact glasses formed under very reducing conditions and, because of their small size, were easily oxidized in air while still molten, or they formed under a variety of different oxygen fugacities resulting in different Fe oxidation states. In the first case, the oxidation state and coordination number would imply similar formation conditions as splash‐form tektites, followed by progressive oxidation.  相似文献   

Australasian microtektites from Antarctica: XAS determination of the Fe oxidation state     

Gabriele Giuli  Maria Rita Cicconi  Sigrid Griet Eeckhout  Giovanni Pratesi  Eleonora Paris  Luigi Folco 《Meteoritics & planetary science》2014,49(4):696-705

The Fe oxidation state and coordination number of 29 impact glass spherules recently recovered from the Transantarctic Mountains (Antarctica) have been determined by X‐ray absorption near edge structure (XANES) spectroscopy. Based on geochemical, isotopic, and fission track data, these spherules are considered as microtektites from the Australasian tektite/microtektite strewn field. Their find location is the farthest so far discovered from the possible source crater region, and their alkali content is the lowest compared with other published data on Australasian microtektite glasses. The Fe³⁺/(Fe²⁺+Fe³⁺) ratio, determined from the analysis of the pre‐edge peak energy position and integrated intensity, is below 0.1 (±0.04) for all the samples, and is comparable to that of most tektites and microtektites from the Australasian strewn field. Also, the pre‐edge peak integrated intensity, which is sensitive to the average Fe coordination geometry, is comparable to that of other Australasian microtektites reported in the literature. The agreement of the Fe oxidation state and coordination number, between the Transantarctic Mountain microtektites (TAM) and the Australasian tektites and microtektites, further confirms the impact origin of these glass spherules and provides an independent suggestion that they represent a major extension southeastward of the Australasian strewn field. The fact that similar redox conditions are observed in tektites and microtektites within the Australasian strewn field regardless of the distance from the source crater area (up to approximately 11000 km) could be an important constraint for better understanding the different processes affecting microtektite formation and transport. The fact that the Fe oxidation state of microtektites does not increase with distance, as in the case of North American microtektites, means that thermal and redox histories of Australasian and TAM microtektites could differ significantly from those of North American microtektites.  相似文献   

Magnetic braking during star formation I     

J. Gillis  L. Mestel  R. B. Paris 《Astrophysics and Space Science》1974,27(1):167-194

We study the transport of angular momentum from a cool massive gas cloud by Alfvén waves travelling along the distorted magnetic field linking the cloud with the hot galactic background. The efficiency of braking is never so great as to keep the cloud even roughly corotating with the back-ground. The mathematical approximations are not quite sharp enough to give a definitive answer to the question: is the braking ever so efficient that the centrifugal forces are kept well below gravity, so that the cloud contracts at the (magnetically-diluted) free-fall rate?; or is the cloud maintained in approximate centrifugal balance, with the rate of contractiondetermined by the loss of angular momentum?  相似文献   

Carbonate alteration associated with talc-chlorite mineralization in the eastern Pyrenees, with emphasis on the St. Barthelemy Massif     

P. Boulvais  P. de Parseval  A. D’Hulst  P. Paris 《Mineralogy and Petrology》2006,88(3-4):499-526

Summary The eastern Pyrenees host a large number of talc-chlorite mineralizations of Albian age (112–97 Ma), the largest of which occur in the St. Barthelemy massif. There talc develops by hydrothermal replacement of dolostones, which were formed by alteration of calcite marbles. This alteration is progressive. Unaltered calcite marbles have oxygen isotope composition of about 25‰ (V-SMOW). The δ¹⁸O values decrease down to values of 12‰ towards the contact with dolostones. This ¹⁸O depletion is accompanied by Mg enrichment, LREE fractionation and systematic shifts in the Sr isotope compositions, which vary from ⁸⁷Sr/⁸⁶Sr = 0.7087–0.7092 in unaltered calcite marbles to slightly more radiogenic compositions with ⁸⁷Sr/⁸⁶Sr = 0.7094 near dolomitization fronts. Dolostones have δ¹⁸O values (about 9‰) lower than calcitic marbles, higher REE content and more radiogenic Sr isotope composition (⁸⁷Sr/⁸⁶Sr = 0.7109 to 0.7130). Hydrothermal calcites have δ¹⁸O values close to dolostones but substantially lower δ¹³C values, down to −6.5‰, which is indicative of the contribution of organic matter. The REE content of hydrothermal calcite is one order of magnitude higher than that of calcitic marbles. Its highly radiogenic Sr composition with ⁸⁷Sr/⁸⁶Sr = 0.7091 to 0.7132 suggests that these elements were derived from silicate rocks, which experienced intense chlorite alteration during mineralization. The chemical and isotopic compositions of the calcite marbles, the dolostones and the hydrothermal calcites are interpreted as products of successive stages of fluid-rock interaction with increasing fluid-rock ratios. The hydrothermal quartz, calcite, talc and chlorite are in global mutual isotopic equilibrium. This allows the calculation of the O isotope composition of the infiltrating water at 300 °C, which is in the δ¹⁸O = 2–4.5‰ range. Hydrogen isotope compositions of talc and chlorite indicate a δD = 0 to −20‰. This water probably derived from seawater, with minor contribution of evolved continental water.  相似文献