Seismic motion in urban sites consisting of blocks in welded contact with a soft layer overlying a hard half-space     

Jean-Philippe Groby  Armand Wirgin 《Geophysical Journal International》2008,172(2):725-758

We address the problem of the response to a seismic wave of an urban site consisting of   N _b   blocks overlying a soft layer underlain by a hard substratum. The results of a theoretical analysis, appealing to a space–frequency mode-matching (MM) technique, are compared to those obtained by a space–time finite-element (FE) technique. The two methods are shown to give rise to the same prediction of the seismic response for   N _b = 1  , 2 and 40 blocks. The mechanism of the interaction between blocks and the ground, as well as that of the mutual interaction between blocks, are studied. It is shown, in the first part of this paper, that the presence of a small number of blocks modifies the seismic disturbance in a manner which evokes qualitatively, but not quantitatively, what was observed during the 1985 Michoacan earthquake in Mexico City. Anomalous earthquake response at a much greater level, in terms of duration, peak and cumulative amplitude of motion, is shown, by a theoretical and numerical analysis in the second part of this paper, to be induced by the presence of a large (≥10) number of identical equi-spaced blocks that are present in certain districts of many cities.  相似文献   

Stock Origins of Subadult and Adult Atlantic Sturgeon, Acipenser oxyrinchus, in a Non-natal Estuary, Long Island Sound     

John R. Waldman  Tim King  Tom Savoy  Lorraine Maceda  Cheryl Grunwald  Isaac Wirgin 《Estuaries and Coasts》2013,36(2):257-267

The anadromous acipenserid Atlantic sturgeon Acipenser oxyrinchus was listed in 2012 under the U.S. Endangered Species Act as having four endangered and one threatened distinct population segment (DPS) in American waters. Anthropogenic activities outside of natal estuaries, particularly bycatch, may hinder the abilities of some populations to rebuild. Most Atlantic sturgeon are residential for their first 2–6 years within their natal estuaries, whereas older subadults and adults may migrate to non-natal estuaries and coastal locations. Previous studies demonstrated that subadults and adults aggregate during summer at locations in Long Island Sound (LIS) and its tributary, the Connecticut River; however, the population origin of these fish is unknown. Because of its geographic proximity and relatively robust population, we hypothesized that the LIS and Connecticut River aggregations were almost solely derived from the Hudson River. We used microsatellite nuclear DNA analysis at 11 loci and mitochondrial DNA control region sequence analyses to estimate the relative contributions of nine Atlantic sturgeon populations and the five DPS to these aggregations using individual-based assignment tests and mixed-stock analysis. From 64 to 73 % of specimens from LIS were estimated to be of Hudson origin. Similarly, 66–76 % of specimens from the Connecticut River were of Hudson origin. However, moderate numbers of specimens were detected from distant spawning populations in the southeastern DPS and from two populations once thought to be extirpated or nearly so, the James River (6–7.3 %), and the Delaware River (7.6–12 %). Additionally, specimens were detected from all five DPS in both the LIS and Connecticut River collections. These results highlight the difficulty of evaluating the status of individual Atlantic sturgeon populations because of the propensity of subadults and adults to migrate for extended duration to distant sites where they may be vulnerable to anthropogenic disturbances.  相似文献   

High pressure-high temperature laboratory apparatus for the measurement of deep sea sediment physical properties     

Roger Morin  Armand J. Silva 《Ocean Engineering》1983,10(6):481-487

Laboratory equipment has been built which will measure the permeability and thermal conductivity of deep-sea sediments at their in-situ conditions of hydrostatic pressure, temperature, and void ratio. The apparatus has the capability of uniaxially consolidating a sediment sample to simulate compaction within the sediment column, while exposing the specimen to hydrostatic pressures ranging from atmospheric to 62 MPa and to temperatures from 22 to 220°C. The equipment includes a hypodermic needle mounted vertically through the base of the pressure vessel from which thermal conductivity is determined by the needle probe method. The system also features a combination of dead-weight testers which produces a small hydraulic gradient across the sample and permits the measurement of sediment permeability at large hydrostatic pressures.The physical property data generated from this apparatus will be important in understanding the mechanisms of heat transfer through the ocean floor and in analysing the coupled flow of heat and pore fluid in the vicinity of a heat source, such as a radioactive waste canister, buried in the seabed.  相似文献   

Contribution de l'aeromagnetisme a l'etude du golfe de Valence (Mediterranee occidentale)     

Armand Galdeano  Jean Claude Rossignol 《Earth and Planetary Science Letters》1977,34(1):85-99

We present an aeromagnetic survey of the Gulf of Valencia and the Balearic Islands (western Mediterranean). A total field anomaly map and a map of the anomalies reduced to the pole have been obtained. From these maps, it is apparent that there are two regions of opposing magnetic style: the Balearic archipelago which is magnetically very smooth, and the north Balearic basin (or Gulf of Valencia) where anomalies are in places very intense. From a comparison of these two domains, we conclude that the Valencian basin was created during an extensional tectonic phase.  相似文献   

Colonisation d'une population d'Oscillatoria rubescens (Cyanophyceae) par une bacterie epiphyte     

Mauricette Feuillade  Armand Bianchi  Jean Claude Druart  Olivier L. Reymond 《Aquatic Sciences - Research Across Boundaries》1989,51(1):59-66

The presence of unknown bacteria upon filaments of the CyanophyteOscillatoria rubescens was observed in the Lake Leman (Lake of Geneva) during Autumn 1985. Conditions of this colonization and the morphology of the association are described. These bacteria probably belong to theCaulobacter group. To explain this colonization we suggest that bacteria respond chemotactically to Cyanophyte exudates.

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Colonisation d'une population d'Oscillatoria rubescens (Cyanophyceae) par une bacterie epiphyte

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Simulation of seismic response in an idealized city     

Chrysoula Tsogka  Armand Wirgin   《Soil Dynamics and Earthquake Engineering》2003,23(5):391-402

We study the seismic response of an idealized 2D ‘city’, constituted by ten non equally-spaced, non equally-sized, homogenized blocks (i.e. buildings or groups of buildings) anchored in a soft soil layer overlying a hard halfspace. Our results display strong response inside the blocks and on the ground which qualitatively match the responses observed in some earthquake-prone cities.  相似文献   

Erratum à la « Perspective » / Erratum to the ‘Perspective’ About shape and development of sterile bodies in phosphatic deposits: [C. R. Geoscience 334 (2002) 1113]     

Armand Boujo 《Comptes Rendus Geoscience》2003,335(12):931

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Acquisition of long wavelength magnetic anomalies pre-dates continental drift     

Armand Galdeano 《Physics of the Earth and Planetary Interiors》1983,32(4):289-292

Using the low altitude MAGSAT satellite data, NASA recently published a new global magnetic map of anomalies. Using this new accurate map and paleomagnetic reconstructions of Gondwanaland, we point out that long wavelength anomalies were continuous in continents that are presently separated. Thus, continental drift would not significantly affect the geometry of these deep-source anomalies. Accordingly, the magnetization of the rocks responsible for these anomalies should mainly be induced.  相似文献   

A soft hydrological monitoring approach for comparing runoff on a network of small poorly gauged catchments     

Armand Crabit  François Colin  Roger Moussa 《水文研究》2011,25(18):2785-2800

Catchments in many parts of the world are either ungauged or poorly gauged, and the dominant processes governing their streamflow response are still poorly understood. The analysis of runoff coefficients provides essential insight into catchment response, particularly if both range of catchments and a range of events are compared. This paper investigates how well the hydrological runoff of 11 small, poorly gauged catchments with ephemeral streams (0·1‐0·6 km²) can be compared using estimated runoff with the associated uncertainty. Data of rainfall and water depth at a catchment's outlet were recorded using automatic logging equipment during 2008‐2009. The hydrological regime is intermittent and the annual precipitation ranged between 569 and 727 mm. Discharge was estimated using Manning's equation and channel cross‐section measurements. Innovative work has been performed under controlled experimental conditions to estimate Manning's coefficient values for the different cover types observed in studied streams: non‐aquatic vegetations (giant reed, bramble and thistle), grass and coarse granular deposits. The results show that estimates derived using roughness coefficients differ from those previously established for larger streams with aquatic vegetation. Catchment runoff was compared at both the event and the annual scale. The results indicate significant variability between the catchment's responses. This variability allows for classification in spite of all the uncertainty associated with runoff estimation. This study highlights the potential of using a network of poorly gauged catch ments. From almost no catchment understanding the proposed methodology allows to compare poorly gauged catchments and highlights similarity/dissimilarity between catchment responses. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Geogas transport in fractured hard rock – Correlations with mining seismicity at 3.54 km depth, TauTona gold mine, South Africa     

Johanna Lippmann-Pipke  Jörg Erzinger  Martin Zimmer  Christian Kujawa  Margaret Boettcher  Esta Van Heerden  Armand Bester  Hannes Moller  Nicole A. Stroncik  Zeev Reches 《Applied Geochemistry》2011,26(12):2134-2146

An on-site gas monitoring study has been conducted in the framework of an earthquake laboratory (The International NELSAM–DAFGAS projects) at the TauTona gold mine, South Africa. Five boreholes up to 60 m long were drilled at 3.54 km depth into the highly fractured Pretorius Fault Zone and instruments for chemical and seismic monitoring installed therein. Over the span of 4 years sensitive gas monitoring devices were continuously improved to enable the direct observation of geogas concentration variations in the DAFGAS borehole. The major gas concentrations are constant and air-like with about 78% N₂, 21% O₂, 1% Ar. The geogas components CO₂, CH₄, He and H₂ show the most interesting trends and variations on the minute-by-minute basis and significantly correlate with seismic data, while the ²²²Rn activity remains constant. Time series and cross correlation analysis allow the identification of different gas components (geogas and tunnel air) and the identification of two processes influencing the borehole gas composition: (1) pumping-induced tunnel air breakthrough through networks of initially water-saturated fault fractures; and (2) seismicity induced permeability enhancement of fault fractures to above ∼5 × 10^-10 m². The current set-up of the gas monitoring system is sensitive enough to quantify the resulting geogas transport during periods of intense blasting activities (including recorded blasts with seismic moment ?1 × 10⁹ Nm, located within 1000 m of the cubby) and, it is suggested, also during induced earthquakes, a final goal of the project.  相似文献