The Meteoritical Bulletin,No. 105

Meteoritical Bulletin 105 contains 2666 meteorites including 12 falls (Aouinet Legraa, Banma, Buritizal, Ejby, Kamargaon, Moshampa, Mount Blanco, Murrili, Osceola, Sariçiçek, Sidi Ali Ou Azza, Stubenberg), with 2244 ordinary chondrites, 142 HED achondrites, 116 carbonaceous chondrites, 37 Lunar meteorites, 20 enstatite chondrites, 20 iron meteorites, 20 ureilites, 19 Martian meteorites, 12 Rumuruti chondrites, 10 primitive achondrites, 9 mesosiderites, 5 angrites, 4 pallasites, 4 ungrouped achondrites, 2 ungrouped chondrites, 1 enstatite achondrite, and 1 relict meteorite, and with 1545 from Antarctica, 686 from Africa, 245 from Asia, 147 from South America, 22 from North America, 14 from Europe, 5 from Oceania, 1 from unknown origin. Note: 5 meteorites from Russia were counted as European. It also includes a list of approved new Dense Collection Areas and a nomenclature of the Aletai (IIIE‐an) iron meteorites from Xinjiang, China.     

The influence of preform on the modes of vibrating beams

A theoretical analysis is presented of a vibratory system in which it is possible to eliminate an unwanted mode of vibration by using that mode as an initial deformation of the system. The analysis shows that this is possible in straight beams with end restraints in axial deformation. The mathematical problem leads to an eigenvalue problem of a type not normally encountered. In the paper examples are given for the changes in eigenfrequency and mode shape produced by the initial preformed shape of the beam for cases where the preform is proportional to a mode of the straight beam and when the preform is unrelated to any mode. The analysis shows that, while elimination of a mode in the strict sense is not achieved, the results can be interpreted for practical purposes in this way.     

Multivariate density model comparison for multi-site flood-risk rainfall in the French Mediterranean area

The French Mediterranean area is subject to intense rainfall events which might cause flash floods, the main natural hazard in the area. Flood-risk rainfall is defined as rainfall with a high spatial average and encompasses rainfall which might lead to flash floods. We aim to compare eight multivariate density models for multi-site flood-risk rainfall. In particular, an accurate characterization of the spatial variability of flood-risk rainfall is crucial to help understand flash flood processes. Daily data from eight rain gauge stations at the Gardon at Anduze, a small Mediterranean catchment, are used in this work. Each multivariate density model is made of a combination of a marginal model and a dependence structure. Two marginal models are considered: the Gamma distribution (parametric) and the Log-Normal mixture (non-parametric). Four dependence structures are included in the comparison: Gaussian, Student t, Skew Normal and Skew t in increasing order of complexity. They possess a representative set of theoretical properties (symmetry/asymmetry and asymptotic dependence/independence). The multivariate models are compared in terms of three types of criteria: (1) separate evaluation of the goodness-of-fit of the margins and of the dependence structures, (2) model selection with a leave-one-out evaluation of the Anderson-Darling and Cramer-Von Mises statistics and (3) comparison in terms of two hydrologically interpretable quantities (return periods of the spatial average and conditional probabilities of exceedances). The key outcome of the comparison is that the Skew Normal with the Log-Normal mixture margins outperform significantly the other models. The asymmetry introduced by the Skew Normal is an added-value with respect to the Gaussian. Therefore, the Gaussian dependence structure, although widely used in the literature, is not recommended for the data in this study. In contrast, the asymptotically dependent models did not provide a significant improvement over the asymptotically independent ones.     

天然地震接收函数揭示的青藏

1998年 6～ 1 1月 ,中国地质科学院与法国 Joseph大学地球物理及构造研究所合作 ,在青海共和至玉树公路沿线 ,布置了40台 Minititan三分量地震仪和 1 3台 CEIS单分量地震仪 ,进行天然地震观测 .研究区位于班公—怒江断裂以北、柴达木以东、中祁连断裂以南和龙门山断裂以西的区域 .沿线穿过南祁连、东昆仑、巴颜喀拉、金沙江等 ,横穿了青藏高原东部的大部分区域(图 1 ) .此剖面是第一次穿越青藏高原东部的地震探测剖面 ,它有利于与中部已有的研究成果进行对比 ,便于探讨在印度大陆向北俯冲的过程中 ,对青藏高原东部深部特征的影响 ,特别是…     

Response of fixed offshore structures in random sea

An integrated model is developed for the short-term and long-term dynamic response of an offshore structure subjected to random wave excitation. A discrete linear, elastic model of the upper structure is coupled with an iterative linear quasi-three-dimensional finite element model for the pile-soil medium, and the system is subjected to stochastic storms described by mean rate of arrival, joint probability distribution of storm duration and average intensity, and a random process that describes the variations of a statistical wave height measure during each storm. Sarpkaya's 1977 experimental information is used to specify values for C_M and C_D, in Morison's equation, consistent with the flow and response characteristics. Soil (clay) degradation, due to cyclic excitation, is followed during the passage of a storm. The indicator of soil degradation is taken to be the value of the horizontal foundation stiffness and the stiffness degradation is modelled by a homogeneous Markov process.     

Lattice Boltzmann simulation of turbulence-induced flocculation of cohesive sediment

Both the floc formation and floc breakup of cohesive sediment are affected by turbulent shear which is recognized as one of the most important parameters, and thus, on the settling and transport of cohesive sediment. In this study, the development of floc characteristics at early stage and steady-state of flocculation were investigated via a three-dimensional lattice Boltzmann numerical model for turbulence-induced flocculation. Simulations for collision and aggregation of various size particles, floc growth, and breakup in isotropic and homogenous turbulent flows with different shear stresses were conducted. Model results for the temporal evolution of floc size distribution show that the normalized floc size distributions is time-independent during early stage of flocculation, and at steady-state, shear rate has no effect on the shape of normalized floc size distribution. Furthermore, the size, settling velocity, and effective density of flocs at the non-equilibrium flocculation stage do not change significantly for shear stresses in the range 0–0.4 N m^?2. The relationships between floc size and settling velocity established during floc growth stages and that during steady-states are different.     

Characterization of subsurface fluxes at the plot scale during flash floods in the Valescure catchment,France

This study focuses on a 10-m² plot within a granitic hillslope in Cevennes mountainous area in France, in order to study infiltration and subsurface hydrological processes during heavy rainfalls and flash floods. The monitoring device included water content at several depths (0–70 cm for the shallow soil water; 0–10 m for the deep water) during both intense artificial and natural rainfall events, chemical and physical tracers, time-lapse electrical resistivity tomography. During the most intense events, the infiltrated water was estimated to be some hundreds of millimetres, which largely exceeds the topsoil capacity (≤40 cm deep in most of the cases). The weathered/fractured rock area below the soil clearly has an active role in the water storage and sub-surface flow dynamics. Vertical flow was dominant in the first 0–10 m, and lateral flow was effective at 8–10 m depth, at the top of the saturated area. The speed of the vertical flow was estimated between 1 and 10 m/hr, whereas it was estimated between 0.1 and 1 m/hr for the lateral flow. The interpretation of the experiments might lead to a local pattern of the 2D-hydrological processes and profile properties, which could be generic for most of the mountainous catchments under Mediterranean climate. It suggests that fast triggering of floods at the catchment scale cannot be explained by a mass transfer within the hillslope, but should be due to a pressure wave propagation through the bedrock fractures, which allows exfiltration of the water downstream the hillslope.     

The age of SNC meteorites and the antiquity of the Martian surface

We report new Sm-Nd, Lu-Hf, and Pb-Pb mineral and whole-rock isotope data for the basaltic shergottite Zagami, as well as Pb-Pb whole-rock isotope data for the basaltic shergottite Los Angeles, the lherzolitic shergottite Dar-al-Gani 476 (DaG 476), and the clinopyroxenite Nakhla. In agreement with previous findings, our new Sm-Nd and Lu-Hf mineral ages on the Martian meteorite Zagami are young (155 and 185 Ma, respectively). The ²⁰⁷Pb/²⁰⁶Pb-²⁰⁴Pb/²⁰⁶Pb compositions of the insoluble fractions of shergottites (Zagami, Los Angeles, and literature data for Shergotty and EETA79001) form an excellent alignment indicative of a 4.0 Ga crystallization age. The range of Pb isotope compositions observed in the leachates of these samples attests to negligible contamination of the shergottites by terrestrial Pb and argues against mixing relationships. The age of 4.048 ± 0.017 Ga (MSWD = 1.5) provided by the Pb isotope compositions of the Zagami whole-rock and residues is therefore taken to date the crystallization of this rock, which, so far, was believed to be only ∼ 180 Ma old. Based on this result, we argue that the lithosphere of Mars is extremely old and that most mineral ages were reset recently by acidic aqueous solutions percolating through the Martian surface. This interpretation is consistent with photographic interpretations of erosional features on Mars. It also relieves the constraint imposed by the presence of anomalies of ¹⁴²Nd and ¹⁸²W (both products of extinct radioactive nuclides) that the Martian mantle should have preserved primordial isotopic heterogeneities, thus allowing for the planet interior to be actively convecting.     

Particulate contribution to extinction of visible radiation: Pollution, haze, and fog

A data set acquired by eight particle-dedicated instruments set up on the SIRTA (Site Instrumental de Recherche par Télédétection Atmosphérique, which is French for Instrumented Site for Atmospheric Remote Sensing Research) during the ParisFog field campaign are exploited to document microphysical properties of particles contributing to extinction of visible radiation in variable situations. The study focuses on a 48-hour period when atmospheric conditions are highly variable: relative humidity changes between 50 and 100%, visibility ranges between 65 and 35 000 m, the site is either downwind the Paris area either under maritime influence. A dense and homogeneous fog formed during the night by radiative cooling. In 6 h, visibility decreased down from 30 000 m in the clear-sky regime to 65 m within the fog, because of advected urban pollution (factor 3 to 4 in visibility reduction), aerosol hydration (factor 20) and aerosol activation (factor 6). Computations of aerosol optical properties, based on Mie theory, show that extinction in clear-sky regime is due equally to the ultrafine modes and to the accumulation mode. Extinction by haze is due to hydrated aerosol particles distributed in the accumulation mode, defined by a geometric mean diameter of 0.6 μm and a geometric standard deviation of 1.4. These hydrated aerosol particles still contribute by 20 ± 10% to extinction in the fog. The complementary extinction is due to fog droplets distributed around the geometric mean diameter of 3.2 μm with a geometric standard deviation of 1.5 during the first fog development stage. The study also shows that the experimental set-up could not count all fog droplets during the second and third fog development stages.