The quantification of low-probability–high-consequences events: part I. A generic multi-risk approach     

Arnaud Mignan  Stefan Wiemer  Domenico Giardini 《Natural Hazards》2014,73(3):1999-2022

Dynamic risk processes, which involve interactions at the hazard and risk levels, have yet to be clearly understood and properly integrated into probabilistic risk assessment. While much attention has been given to this aspect lately, most studies remain limited to a small number of site-specific multi-risk scenarios. We present a generic probabilistic framework based on the sequential Monte Carlo Method to implement coinciding events and triggered chains of events (using a variant of a Markov chain), as well as time-variant vulnerability and exposure. We consider generic perils based on analogies with real ones, natural and man-made. Each simulated time series corresponds to one risk scenario, and the analysis of multiple time series allows for the probabilistic assessment of losses and for the recognition of more or less probable risk paths, including extremes or low-probability–high-consequences chains of events. We find that extreme events can be captured by adding more knowledge on potential interaction processes using in a brick-by-brick approach. We introduce the concept of risk migration matrix to evaluate how multi-risk participates to the emergence of extremes, and we show that risk migration (i.e., clustering of losses) and risk amplification (i.e., loss amplification at higher losses) are the two main causes for their occurrence.  相似文献   

Modeling nutrients profiles at the sediment–water interface. Calibration and validation from two climatically contrasted estuaries: Seine (France) and Somone (Senegal)     

Valérie Mesnage  Nicolas Lecoq  Issa Sakho  Arnaud Vennin 《Comptes Rendus Geoscience》2013,345(11-12):439-445

The dialysis porewater sampler, type Hesslein, allows sampling of sediment interstitial water according to a continuous gradient between sediment and the water column. Its equilibration time fluctuates according to the nature of sediment, so it has to be measured in each kind of sediment. The aim of this work is to develop a physical diffusion model in order to determine an equilibration time without using extensive field experiments. The model is validated by real nutrient concentration profiles obtained on two estuaries under different climates, moderate climate (estuary of the Seine) and tropical dry climate (estuary of Somone, Senegal). The results highlight that the equilibration of the dialysis porewater sampler is not homogeneous over the full sediment height investigated. Other sediment characteristics as compaction, rate of bioturbation or bacterial density must be taken into account in order to find a well-calculated value of the equilibration time.  相似文献   

The 2011 Draconids: The First European Airborne Meteor Observation Campaign     

Jeremie Vaubaillon  Pavel Koten  Anastasios Margonis  Juraj Toth  Regina Rudawska  Maria Gritsevich  Joe Zender  Jonathan McAuliffe  Pierre-Dominique Pautet  Peter Jenniskens  Detlef Koschny  Francois Colas  Sylvain Bouley  Lucie Maquet  Arnaud Leroy  Jean Lecacheux  Jiri Borovicka  Junichi Watanabe  Jürgen Oberst 《Earth, Moon, and Planets》2015,114(3-4):137-157

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The hydrodynamics of the Snorre Field area, offshore Norway     

G. Caillet  C. Séjourné  D. Grauls  J. Arnaud 《地学学报》1991,3(2):179-193

The Snorre Field, in the Norwegian North Sea, contains a 300 m oil column and is characterized by high pressures. The Snorre Field and its satellites are a well-documented area and it was considered as an excellent case history for documenting hydrocarbon migration and petroleum hydrodynamics in an overpressured regime. The reservoirs are Triassic and Lower Jurassic sandstones overlain by thick shale formations. The overpressure in the acquifer is 14 MPa. The variations of the oil-water contact levels observed throughout the structure can be correlated with oil density variations. This implies that some faults are partly sealing and suggests that leakage through the cap rock is possible together with a selective input of hydrocarbons within the compartments. The possible mechanisms of pressuring and their consequences on the migration system are discussed in this paper. The origin of abnormal pressures in the reservoir is not directly related to the vertical overburden. Some equivalent overpressures due to the compaction exist further south at the North Alwyn location. An equalization of about 14 MPa overpressure occurs along a SW-NE structural trend, through the North Alwyn, Brent, Statfjord and Snorre fields. Snorre being at the shallowest depth, the pore pressure at the top of the reservoir reaches the stress limit for fracturing and hydrocarbons leak from the field. The idea that a large structural trend acts as a preferential route for the migration of hydrocarbons is well supported; however, the oils in Snorre have a GOR increasing from the southwest to the northeast part of the field and this feature, supported by organic geochemistry, reflects an input of light hydrocarbons from source areas in the adjacent 34/5 basin to the east where high pressures are generated. Evidence for high pressures in the basin exists on seismic profiles, where velocity anomalies indicate highly pressured deep zones and migration possibilities along fractures or unconformities. The pressure regime and the stress conditions are key points for the exploration in this area, together with the sealing capacity of the main faults.  相似文献   

Buoyancy-driven perturbations in a rapidly rotating,electrically conducting fluid: part I – flow and magnetic field     

David E. Loper  Arnaud Chulliat  Hisayoshi Shimizu 《地球物理与天体物理流体动力学》2013,107(6):429-469

The steady velocity, perturbation pressure and perturbation magnetic field, driven by an isolated buoyant parcel of Gaussian shape in a rapidly rotating, unconfined, incompressible electrically conducting fluid in the presence of an imposed uniform magnetic field, are obtained by means of the Fourier transform in the limit of small Ekman number. Lorentz and inertial forces are neglected. The solution requires at most evaluation of a single integral and is found in closed form in some spatial regions. The solution has structure on two disparate scales: on the scale of the buoyant parcel and on the scale of the Taylor column, which is elongated in the direction of the rotation axis. The detailed structures of the flow and pressure depend linearly on the relative orientation of gravity and rotation, with the solution for arbitrary orientation being a linear combination of two limiting cases in which these vectors are colinear (polar case) and perpendicular (equatorial case). The perturbation magnetic field depends additionally on the relative orientation of the imposed magnetic field, and three limiting cases of interest are presented in which gravity and rotation are colinear (polar–toroidal case), gravity and imposed field are colinear (equatorial–radial case) and all three are mutually perpendicular (equatorial–toroidal case). Visualization and analysis of the velocity and perturbation magnetic field vectors are facilitated by dividing these vector fields into geostrophic and ageostrophic protions. In all cases, the geostrophic and ageostrophic portions have different structure on the Taylor-column scale. The buoyancy force is balanced by a pressure force in the polar case and by a flux of momentum in the equatorial case. The pressure force and momentum flux do not decay in strength with increasing axial distance. Far from the parcel, the axial mass flux varies as the inverse one-third power of distance from the parcel. The velocity has a single geostrophic vortex in the polar case and two vortices in the equatorial case. The perturbation magnetic field has two, four and one geostrophic vortices in the polar–toroidal, equatorial–radial and equatorial–toroidal cases, respectively. To facilitate comparison of the present results with numerical simulations carried out in a finite domain, a set of boundary conditions are developed, with may be applied at a finite distance from the parcel.  相似文献   

Optical extinction due to aerosols in the upper haze of Venus: Four years of SOIR/VEX observations from 2006 to 2010     

Valérie Wilquet  Rachel Drummond  Arnaud Mahieux  Séverine Robert  Ann Carine Vandaele  Jean-Loup Bertaux 《Icarus》2012,217(2):875-881

The variability of the aerosol loading in the mesosphere of Venus is investigated from a large data set obtained with SOIR, a channel of the SPICAV instrument suite onboard Venus Express. Vertical profiles of the extinction due to light absorption by aerosols are retrieved from a spectral window around 3.0 μm recorded in many solar occultations (～200) from September 2006 to September 2010. For this period, the continuum of light absorption is analyzed in terms of spatial and temporal variations of the upper haze of Venus. It is shown that there is a high short-term (a few Earth days) and a long-term (～80 Earth days) variability of the extinction profiles within the data set. Latitudinal dependency of the aerosol loading is presented for the entire period considered and for shorter periods of time as well.  相似文献   

Nano dust impacts on spacecraft and boom antenna charging     

Filippo Pantellini  Soraya Belheouane  Nicole Meyer-Vernet  Arnaud Zaslavsky 《Astrophysics and Space Science》2012,341(2):309-314

High rate sampling detectors measuring the potential difference between the main body and boom antennas of interplanetary spacecraft have been shown to be efficient means to measure the voltage pulses induced by nano dust impacts on the spacecraft body itself (see Meyer-Vernet et al. in Sol. Phys. 256:463, 2009). However, rough estimates of the free charge liberated in post impact expanding plasma cloud indicate that the cloud’s own internal electrostatic field is too weak to account for measured pulses as the ones from the TDS instrument on the STEREO spacecraft frequently exceeding 0.1 V/m. In this paper we argue that the detected pulses are not a direct measure of the potential structure of the plasma cloud, but are rather the consequence of a transitional interruption of the photoelectron return current towards the portion of the antenna located within the expanding cloud.  相似文献   

The Planck cluster survey     

J.G. Bartlett  A. Chamballu  J.‐B. Melin  M. Arnaud  Members of the Planck Working 《Astronomische Nachrichten》2008,329(2):147-150

The Planck Satellite will survey the entire sky in 9 millimeter/submillimeter bands and detect thousands of galaxy clusters via their thermal Sunyaev‐Zel'dovich (SZ) effect. The unprecedented volume of the survey will permit the construction of a unique catalog of massive clusters out to redshifts of order unity. We describe the expected contents of this catalog and use an empirical model of the intra‐cluster gas to predict the X‐ray properties of Planck SZ clusters. Using this information we show how a ∼10 Ms follow‐up program on XMM‐Newton could increase by ∼100‐fold the number of clusters with measured temperatures in the redshift range z = 0.5–1. Such a large sample of well‐studied massive clusters at these redshifts would be a powerful cosmological tool and a significant legacy for XMM‐Newton. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

Protracted,coeval crust and mantle melting during Variscan late-orogenic evolution: U–Pb dating in the eastern French Massif Central     

Laurent  Oscar  Couzinié  Simon  Zeh  Armin  Vanderhaeghe  Olivier  Moyen  Jean-François  Villaros  Arnaud  Gardien  Véronique  Chelle-Michou  Cyril 《International Journal of Earth Sciences》2017,106(2):421-451

International Journal of Earth Sciences - The late stages of the Variscan orogeny are characterized by middle to lower crustal melting and intrusion of voluminous granitoids throughout the belt,...  相似文献   

Does global warming favour the occurrence of extreme floods in European Alps? First evidences from a NW Alps proglacial lake sediment record   总被引：2，自引：0，他引：2  

B. Wilhelm  F. Arnaud  D. Enters  F. Allignol  A. Legaz  O. Magand  S. Revillon  C. Giguet-Covex  E. Malet 《Climatic change》2012,113(3-4):563-581

Flood hazard is expected to increase in the context of global warming. However, long time-series of climate and gauge data at high-elevation are too sparse to assess reliably the rate of recurrence of such events in mountain areas. Here paleolimnological techniques were used to assess the evolution of frequency and magnitude of flash flood events in the North-western European Alps since the Little Ice Age (LIA). The aim was to document a possible effect of the post-19^th century global warming on torrential floods frequency and magnitude. Altogether 56 flood deposits were detected from grain size and geochemical measurements performed on gravity cores taken in the proglacial Lake Blanc (2170?m?a.s.l., Belledonne Massif, NW French Alps). The age model relies on radiometric dating (¹³⁷Cs and ²⁴¹Am), historic lead contamination and the correlation of major flood- and earthquake-triggered deposits, with recognized occurrences in historical written archives. The resulting flood calendar spans the last ca 270?years (AD 1740–AD 2007). The magnitude of flood events was inferred from the accumulated sediment mass per flood event and compared with reconstructed or homogenized datasets of precipitation, temperature and glacier variations. Whereas the decennial flood frequency seems to be independent of seasonal precipitation, a relationship with summer temperature fluctuations can be observed at decadal timescales. Most of the extreme flood events took place since the beginning of the 20^th century with the strongest occurring in 2005. Our record thus suggests climate warming is favouring the occurrence of high magnitude torrential flood events in high-altitude catchments.  相似文献