Truncation of the distribution of ground-motion residuals

Recent studies to assess very long-term seismic hazard in the USA and in Europe have highlighted the importance of the upper tail of the ground-motion distribution at the very low annual frequencies of exceedance required by these projects. In particular, the use of an unbounded lognormal distribution to represent the aleatory variability of ground motions leads to very high and potentially unphysical estimates of the expected level of shaking. Current practice in seismic hazard analysis consists of truncating the ground-motion distribution at a fixed number (ε _max) of standard deviations (σ). However, there is a general lack of consensus regarding the truncation level to adopt. This paper investigates whether a physical basis for choosing ε _max can be found, by examining records with large positive residuals from the dataset used to derive one of the ground-motion models of the Next Generation Attenuation (NGA) project. In particular, interpretations of the selected records in terms of causative physical mechanisms are reviewed. This leads to the conclusion that even in well-documented cases, it is not possible to establish a robust correlation between specific physical mechanisms and large values of the residuals, and thus obtain direct physical constraints on ε _max. Alternative approaches based on absolute levels of ground motion and numerical simulations are discussed. However, the choice of ε _max is likely to remain a matter of judgment for the foreseeable future, in view of the large epistemic uncertainties associated with these alternatives. Additional issues arise from the coupling between ε _max and σ, which causes the truncation level in terms of absolute ground motion to be dependent on the predictive equation used. Furthermore, the absolute truncation level implied by ε _max will also be affected if σ is reduced significantly. These factors contribute to rendering a truncation scheme based on a single ε _max value impractical.     

Ground motions observed during the 15 August 2007 Pisco, Peru, earthquake

A M_w 7.9 earthquake event occurred on 15 August 2007 off the coast of central Peru, 60 km west of the city of Pisco. This event is associated with subduction processes at the interface of the Nazca and South American plates, and was characterised by a complex source mechanism involving rupture on two main asperities, with unilateral rupture propagation to the southeast. The rupture process is clearly reflected in the ground motions recorded during this event, which include two separate episodes of strong shaking. The event triggered 18 accelerographic stations; the recordings are examined in terms of their characteristics and compared to the predictions of ground-motion prediction equations for subduction environments, using the maximum-likelihood-based method of Scherbaum et al. (Bull Seismol Soc Am 94(6):2164–2185, 2004). Additionally, macroseismic observations and damage patterns are examined and discussed in the light of local construction practices, drawing on field observations gathered during the post-earthquake reconnaissance missions.     

Experimental synthesis and phase relations of phengitic muscovite from 6.5 to 11 GPa in a calcareous metapelite from the Dabie Mountains, China

The stability and phase relations of phengitic muscovite in a metapelitic bulk composition containing a mixed H₂O+CO₂ fluid were investigated at 6.5–11 GPa, 750–1050°C in synthesis experiments performed in a multianvil apparatus. Starting material consisted of a natural calcareous metapelite from the coesite zone of the Dabie Mountains, China, ultrahigh-pressure metamorphic complex that had experienced peak metamorphic pressures greater than 3 GPa. The sample contains a total of 2.1 wt.% H₂O and 6.3 wt.% CO₂ bound in hydrous and carbonate minerals. No additional fluid was added to the starting material. Phengite is stable in this bulk composition from 6.5 to 9 GPa at 900°C and coexists with an eclogitic phase assemblage consisting of garnet, omphacite, coesite, rutile, and fluid. Phengite dehydrates to produce K-hollandite between 8 and 11 GPa, 750–900°C. Phengite melting/dissolution occurs between 900°C and 975°C at 6.5–8 GPa and is associated with the appearance of kyanite in the phase assemblage. The formation of K-hollandite is accompanied by the appearance of magnesite and topaz-OH in the phase assemblage as well as by significant increases in the grossular content of garnet (average X_grs=0.52, X_py=0.19) and the jadeite content of omphacite (X_jd=0.92). Mass balance indicates that the volatile content of the fluid phase changes markedly at the phengite/K-hollandite phase boundary. At P≤8 GPa, fluid coexisting with phengite appears to be relatively CO₂-rich (XCO₂/XH₂O=2.2), whereas fluid coexisting with K-hollandite and magnesite at 11 GPa is rich in H₂O (XCO₂/XH₂O=0.2). Analysis of quench material and mass balance calculations indicate that fluids at all pressures and temperatures examined contain an abundance of dissolved solutes (approximately 40 mol% at 8 GPa, 60 mol% at 11 GPa) that act to dilute the volatile content of the fluid phase. The average phengite content of muscovite is positively correlated with pressure and ranges from 3.62 Si per formula unit (pfu) at 6.5 GPa to 3.80 Si pfu at 9 GPa. The extent of the phengite substitution in muscovite in this bulk composition appears to be limited to a maximum of 3.80–3.85 Si pfu at P=9 GPa. These experiments show that phengite should be stable in metasediments in mature subduction zones to depths of up to 300 km even under conditions in which aH₂O1. Other high-pressure hydrous phases such as lawsonite, MgMgAl-pumpellyite, and topaz-OH that may form in subducted sediments do not occur within the phengite stability field in this system, and may require more H₂O-rich fluid compositions in order to form. The wide range of conditions under which phengite occurs and its participation in mixed volatile reactions that may buffer the composition of the fluid phase suggest that phengite may significantly influence the nature of metasomatic fluids released from deeply subducted sediments at depths of up to 300 km at convergent plate boundaries.     

The Upper Adriatic borderland: From conflict to harmony

The paper presents an overview of the Upper Adriatic as a contact area between different cultural, social, economic and political entities, producing potential conflicts in the last century. The first part of the 20th century represented a classic example of geopolitical conflict through two World Wars and their related Peace Conferences that deeply impacted the region. Conflicts arising from the mid-century solution of the Trieste question transformed the Upper Adriatic into a laboratory of contemporary political geographic transformation. Changing geopolitical patterns have also modified the political, social and ethnic construction of the Upper Adriatic. The process of creating new international boundaries in the region ended in 1991 with the independence of Slovenia and Croatia. Through these geopolitical transformations in the Upper Adriatic, new political geographic attitudes evolved. Early on, Ratzel's geopolitical principles of defining borders as power barometers between neighbors dominated. More recently, attitudes have reflected modern integrative ideas with a focus on looking for harmony and the elimination of international conflicts. Greater attention has thus been given to the political geography of `everyday life', inter-ethnic relations, and cross-border contacts. Hence, `new' borderlands of the Upper Adriatic are more receptive to integration because they seek to overcome conflicts caused by the division of traditionally homogeneous spaces as local level political and ideological hindrances disappear. The region divided among Italy, Slovenia, and Croatia is becoming a new and special type of European borderland in the new century.     

The scale of ore-depositional systems: an important restraint on epigenetic vs remobilized syngenetic origins for Archaean mesothermal gold deposits

There is general consensus that the majority of gold deposits in the important group hosted by volcanic or intrusive host rocks within Archaean granitoid-greenstone terrains have an epigenetic origin. However, there is controversy surrounding those stratabound deposits hosted by Fe-rich sedimentary rocks, such as banded iron formation (BIF), for which epigenetic, syngenetic and remobilized syngenetic (lateral secretion) origins have all been proposed.In Western Australia, such controversial gold deposits in Fe-rich sedimentary units have similar ore mineralogies, ore-element ratios and, in places, alteration assemblages and, on the craton scale, show very similar structural controls to the other deposits: equivalent relationships are recorded for similar deposits in other cratons. All Western Australian deposits occur along kilometre-scale shear or fault zones linked to trans-craton, obliqueto strike-slip shear zones that were a focus for: i) carbonation with a mantle-like isotopic signature, and ii) emplacement of high-level A- and I-type granitoids, felsic porphyries and/or calc-alkaline lamprophyres. The scale of the mineralizing systems and the broad contemporaneity of mineralization, as indicated by radiogenic isotope studies, is much larger than that envisaged in conceptual secretion models which involve volumetrically small, locally-enriched source rocks. Instead, Archaean gold mineralization in Western Australia, at least, is probably the result of high fluid-flux during deformation, hightemperature metamorphism and magmatism which may be related to tectonism at convergent plate margins, as in modern examples. There is strong evidence for similar tectonic and mineralizing processes from the Canadian Shield.

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Zusammenfassung Goldlagerstätten in vulkanischen oder intrusiven Gesteinskörpern innerhalb von Granitoid-Grünstein Regionen archaischen Alters gelten im allgemeinen als epigenetisch. Unklarheit besteht dagegen bei Lagerstätten, die an eisenreiche Sedimentgesteine wie gebänderte Roteisensteine (banded iron formation (BIF) gebunden sind und für die epigenetische, syngenetische sowie remobilisierte syngenetische (laterale Sekretion) Entstehungstheorien diskutiert werden.In West-Australien gibt es diese kontroversen Goldvorkommen in eisenreichen Sedimentgesteinen. Sie haben ähnliche Lagerstättenmineralogien, Elementverteilungen und z. T. auch ähnliche Umwandlungsprodukte wie die zuerst genannten, eindeutig epigenetischen Goldvorkommen, außerdem erkennt man vergleichbare strukturelle Kontrollen der Lagerstätte und Ähnlichkeiten, wenn sie mit Vorkommen in anderen Kratonen verglichen werden. Alle westaustralischen Lagerstätten befinden sich in trans-kratonischen Scher- und Störungszonen mit kilometergroßen Versatzbeträgen. An diesen Störungszonen fand Inkohlung mit einer den Mantel ähnlichen Isotopensignatur und der Aufstieg von A- und I-Typ Granitoiden, felsischen Porphyren und/oder kalk-alkalischen Lamprophyren statt. Das Größenverhältnis des mineralisierenden Systems und die weitreichende, zeitgleiche Mineralisation, auf die Untersuchungen an radiogenen Isotopen hindeuten, ist viel größer als sie durch Sekretions-Modelle, die auf kleinen Volumina und nur lokal angereichertem Gold im Gestein basieren, prognostiziert werden können.In der Zeit des Archaikums resultiert die Goldanreicherung in West-Australien wahrscheinlich aus einem enormen Lösungsdurchfluß während der Deformation, aus Hoch-Temperatur-Metamorphose und Magmatismus, was in möglichem Zusammenhang mit tektonischen Vorgängen an konvergierenden Plattenrändern, ähnlich modernen Beispielen, steht. Es gibt zahlreiche Hinweise auf entsprechende tektonische und mineralogische Prozesse des Kanadischen Schildes.

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Résumé Il existe un consensus général quant à l'origine épigénétique des dépôts d'or contenus dans les ensemble volcaniques ou intrusifs des formations de granitoïdes — greenstones d'âge archéen. Par contre, une controverse subsiste à propos des dépôts stratiformes contenus dans les roches sédimentaires riches en Fe, telle que la «banded iron formation» (BIF), pour lesquels ont été proposées des origines épigénétique, syngénétique et syngénétique de remobilisation (sécrétion latérale).Il existe en Australie occidentale de tels dépôts d'or situés au sein d'unités sédimentaires riches en Fe. Ces dépots présentent, par rapport aux dépôts épigénétiques du premier type, un certain nombre de similitudes: leur minéralogie, les rapports entre leurs éléments, en certains endroits leurs produits d'altération et, à l'échelle du craton, leurs relations avec la structure. Des similitudes analogues peuvent être relevées à propos de gisements de même type situés dans d'autres cratons. Tous les gisements ouest-autraliens sont localisés le long de zones de failles ou de cisaillement d'échelle kilométrique liées à des shear zones transcratoniques à rejet oblique ou horizontal. Ces zones sont marquées par: 1) une carbonisation avec signature isotopique mantélique; 2) la mise en place de granitoïdes peu profonds de type A et I, de porphyres felsitiques et/ou de lamprophyres calco-alcalins. L'échelle du système minéralisant et la simultanéité des minéralisations révélée par la géochronologie isotopique sont bien supérieures à ce qu'impliqueraient les modèles par sécrétion, qui mettent en jeu des sources de faible volume à enrichissement local.En conclusion, les minéralisations de l'Australie de l'ouest ont probablement pour origine l'action d'un flux important de fluide minéralisant au cours de la déformation, du métamorphisme de haute température et du magmatisme, phénomènes que l'on peut mettre en relation avec une convergence de plaques par analogie avec des exemples récents. Il existe de nombreux indices d'une tectonique et d'une minéralisation analogues dans le bouclier canadien.

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Angular momenta in binary systems

The correlations angular momentaL to massesM are studied for different types of spectroscopic binaries. The functionsL=AM ^b have the coefficientb with the values expected from a Keplerian mechanics, but the valuesA(q, T), A(q, a), A(q, v), associated tob=5/3, 3/2, and 2, respectively, are given (statistically speaking) by multiples or submultiples of discrete values of: the mass ratiosq, the semi-major axesa, periodsT, and velocitiesv of the reduced mass. This indicates the existence of a discrete unit of actionL=(1/2)×potential energy xperiod. Postulates about equivalent states of angular momenta for different orbital parameters are introduced, being this coherent with the analysis of the up-to-date data. Among other examples of the application of such equivalence postulates, we haveL(M) (W-type of the WUMa systems)L(M) (main group of the Algol binaries). The quantum units of action seen here are equivalent to those seen in the solar system in one of our previous works. From comparisons with galaxies and single stars, it is evidence that there is not an unique universal functionL=AM ^b, when the fine structure of the relation is analysed: each type of object has its own coefficients,A, b. It sems to be that there are an upper and a lower limit for all the possible functions. The upper limit isL=A _gM^5/3, withA _g1 associated to periodsT Hubble time, and the lower limit isL=GM ^2/c, with 1. The existence of the upper limit can be investigated with studies of pairs of galaxies, and the lower limit can be tested with analysis of single G, K, M stars. The quantical hypothesis introduced here can be checked definitely, when available larger samples of data with low errors, with similar quality as the selected list of almost 80 eclipsing binaries (mainly detached systems) analysed here.     

A model of the ground surface temperature for micrometeorological analysis

Micrometeorological models at various scales require ground surface temperature, which may not always be measured in sufficient spatial or temporal detail. There is thus a need for a model that can calculate the surface temperature using only widely available weather data, thermal properties of the ground, and surface properties. The vegetated/permeable surface energy balance (VP-SEB) model introduced here requires no a priori knowledge of soil temperature or moisture at any depth. It combines a two-layer characterization of the soil column following the heat conservation law with a sinusoidal function to estimate deep soil temperature, and a simplified procedure for calculating moisture content. A physically based solution is used for each of the energy balance components allowing VP-SEB to be highly portable. VP-SEB was tested using field data measuring bare loess desert soil in dry weather and following rain events. Modeled hourly surface temperature correlated well with the measured data (r ² = 0.95 for a whole year), with a root-mean-square error of 2.77 K. The model was used to generate input for a pedestrian thermal comfort study using the Index of Thermal Stress (ITS). The simulation shows that the thermal stress on a pedestrian standing in the sun on a fully paved surface, which may be over 500 W on a warm summer day, may be as much as 100 W lower on a grass surface exposed to the same meteorological conditions.     

gLucifer: next generation visualization framework for high-performance computational geodynamics

High-performance computing provides unprecedented capabilities to produce higher resolution 4-D models in a fraction of time. Thus, the need exists for a new generation of visualization systems able to maintain parity with the enormous volume of data generated. In attempting to write this much data to disk, each computational step introduces a significant performance bottleneck, yet most existing visualization software packages inherently rely on reading data in from a dump file. Available packages make this assumption of postprocessing at quite a fundamental level and are not very well suited for plotting very large numbers of specialized particles. This necessitates the creation of a new visualization system that meets the needs of large-scale geodynamic modeling. We have developed such a system, gLucifer, using a software framework approach that allows efficient reuse of our efforts in other areas of research. gLucifer is capable of producing movies of a 4-D data set “on the fly” (simultaneously with running the parallel scientific application) without creating a performance bottleneck. By eliminating most of the human efforts involved in visualizing results through postprocessing, gLucifer reconnects the scientist to the numerical experiment as it unfolds. Data sets that were previously very difficult to even manage may be efficiently explored and interrogated without writing to disk, and because this approach is based entirely on memory distributed across as many processors as are being utilized by the scientific application, the visualization solution is scalable into terabytes of data being rendered in real time.     

Mantle melting in equilibrium with an Iron–Wüstite–Graphite buffered COH-fluid

Partial melting experiments on a San Carlos peridotite were done in a Walker type multi-anvil press at pressures from 5 to 12.5 GPa. Experiments were done in the presence of a COH-fluid and at oxygen fugacity controlled by the Fe–FeO buffer. Olivine, clinopyroxene, garnet and orthopyroxene are stable in all but the highest temperature 10 GPa experiments where olivine and garnet coexist, and the highest temperature 5 GPa experiments where olivine is the single crystalline phase. The solidus at 5 GPa was found to be at approximately 1,200°C and the liquidus was estimated to be at 1,325°C, which is ∼500°C lower than has been reported for dry melting of peridotite. The aluminum concentration of the melts decreases with increasing melt fraction and decreases also with increasing pressure. At 5 GPa the melts have a CaO/Al₂O₃-ratio of 0.85–1.0, which is similar to that of undepleted komatiites; major element concentrations are also identical to those of undepleted komatiites such as the Munro komatiites. At 10 and 12.5 GPa the partial melts have CaO/Al₂O₃-ratios above 1.5 and major element composition almost identical to aluminum depleted komatiites such as the Barberton komatiites. We therefore conclude that in the presence of a reducing COH-fluid both aluminum-depleted and -undepleted komatiites could have formed at temperatures much lower than generally accepted.     

A Practical Approach to Mine Equipment Sizing in Relation to Dig-Limit Optimization in Complex Orebodies: Multi-Rock Type,Multi-Process,and Multi-Metal Case

Equipment sizing is a developed field of mining engineering, which considers all aspects related to productivity, and grade distribution. Current methods of equipment sizing consider block dilution, but do not analyze the impact of the selectivity changes on practical dig-limits. This research analyzed the impact of varying equipment sizes on a highly variable three destination, Au and Cu bench, in a sulfide/oxide deposit. The study shows that selectivity sizing profit and size relationships are nonlinear, and exhibit severe break points if insufficiently selective equipment is used. The proposed technique can be used for sizing mine equipment in complex deposits.