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   

Apparent Attenuation and Dispersion Arising in Seismic Body-Wave Velocity Retrieval     

Armand Wirgin 《Pure and Applied Geophysics》2016,173(7):2473-2488

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Geometry and Properties of the Excavation-Induced Fractures at the Meuse/Haute-Marne URL Drifts   总被引：1，自引：1，他引：0  

G. Armand  F. Leveau  C. Nussbaum  R. de La Vaissiere  A. Noiret  D. Jaeggi  P. Landrein  C. Righini 《Rock Mechanics and Rock Engineering》2014,47(1):21-41

The performance and safety assessment and technology demonstration are the main objectives of research programs for feasibility studies for deep geological repository of radioactive waste. In this context, the French national radioactive waste management agency (ANDRA) started to develop the Meuse/Haute-Marne underground research laboratory (URL) at Bure, nearly 300 km East of Paris. The host formation consists of a Callovo-Oxfordian claystone found between 420 and 550 m below ground, overlain and underlain by poorly permeable carbonate formations. One of the major concerns related to performance assessment is the excavation-induced fractures which may provide groundwater preferential pathway for radionuclide migration. The extent of the fractures possibly acting significantly in the radionuclide migration is known as the excavation damaged zone (EDZ). A scientific study on the EDZ characterization is performed at the main level of the URL (?490 m). Observations such as structural analysis on core, overcored resin-filled samples, geological survey of the drift face and sidewalls, were made to better understand the fracture network characteristics, extent and its generation. Pulse and constant head test hydraulic conductivity measurements were performed with multi packer system to estimate the extension of the EDZ hydraulic conductivity. Fractures exhibited high transmissivity near the excavation walls, but farther from the exaction walls, shear fractures showed hydraulic conductivity values reflecting values of undisturbed or slightly disturbed rock mass condition. The major findings in terms of geometry and properties of excavation-induced fractures are discussed in detail in this paper. For example, it is observed that the shape of the fracture network depends on the orientation of the drift in relation to the orientation of the in situ stress field.  相似文献   

A spectrophotometric measurement of soil cation exchange capacity based on cobaltihexamine chloride absorbance     

Delphine Aran  Armand Maul  Jean-Franois Masfaraud 《Comptes Rendus Geoscience》2008,340(12):865-871

Among numerous methods for cation exchange capacity (CEC) determination for soils and sediments, the cobaltihexamine chloride method is frequently used due to its ability to measure CEC at soil pH. After exchange with Co(NH₃)₆³⁺ ions, CEC is estimated via the measurement of the Co remaining in solution. The modified method proposed allows a more rapid determination of CEC based on the measurement of the absorbance at 472 nm of the cobaltihexamine chloride solution before and after exchange. This method has been applied to various soil's horizons from four sites, selected to cover a wide range of CEC and pH values. The model obtained allows one to calculate CEC from absorbance at 472 nm with 95% confidence intervals. As CEC is of relevant meaning in agronomical and environmental purposes, and more recently in ecotoxicological studies, this modified method can be proposed as a rapid test for CEC evaluation.  相似文献   

An analysis of 3.5 kHz acoustic reflections and sediment physical properties     

Kenneth C. Baldwin  Lester R. LeBlanc  Armand J. Silva 《Ocean Engineering》1985,12(6):475-492

Near-bottom normal incidence acoustic reflection data and sediment physical property data are used to study the relationships between acoustic reflections and sediment physical properties. A pinger-hydrophone experiment was performed to obtain the necessary acoustic reflection data. In addition, a standard piston core was retrieved in the acoustic survey area for physical property analysis. The piston core was sampled and 13 properties were measured at 55 locations within the top 12 m of the core. Correlation studies amongst the sediment physical properties resulted in the following strong correlations: acoustic impedance ($\text{Z}$) and porosity ($\text{N}$), (0.96); water content ($\text{WC}$) and $\text{Z}$, (0.95); bulk density ($\text{BD}$) and $\text{Z}$, (0.99).The empirical orthonormal function (EOF) method was employed for acoustic signal analysis. This method assumes no a-priori models of the sediment or causality. The EOF method reduced the acoustic data to 8 functions that contained 97.6% of the sample variance. The EOFs were subsequently analysed by using cepstrum analysis which reveals time delay information and enhances detecting zones of reflectivity. The result of the sediment physical property and cepstrum analysis indicates that zones of reflectivity are essentially zones of relatively high acoustic impedance, low porosity, and low phi (high mean grain size).  相似文献   

Two-dimensional ground motion at a soft viscoelastic layer/hard substratum site in response to SH cylindrical seismic waves radiated by deep and shallow line sources—II. Numerical results     

Jean-Philippe Groby  Armand Wirgin 《Geophysical Journal International》2005,163(1):192-224

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Simulation of seismic response in a city-like environment   总被引：1，自引：0，他引：1  

Jean-Philippe Groby  Chrysoula Tsogka  Armand Wirgin   《Soil Dynamics and Earthquake Engineering》2005,25(7-10):487-504

We study the seismic response of idealized 2D cities, constituted by non-equally spaced, non-equally sized homogenized blocks anchored in a soft layer overlying a hard half space. The blocks and soft layer are occupied by dissipative media. To simulate such response, we use an approximation of the viscoelastic modulus by a low-order rational function of frequency and incorporate this approximation into a first-order-in-time scheme. Our results display spatially variable, strong, long-duration responses inside the blocks and on the ground, which qualitatively match the responses observed in some earthquake-prone cities of Mexico, France, the USA, etc.  相似文献   

Evaluation of antifouling properties of non-toxic marine paints     

Abdellatif Mellouki  Armand Bianchi  Alain Perichaud  Georges Sauvet 《Marine pollution bulletin》1989,20(12):612-615

The most common way to prevent biofouling of immersed surfaces is to coat the exposed surfaces with a paint containing a biocide acting on marine organisms by diffusion into the surrounding water. However diffusion of toxins into the marine environment causes pollution and serious economic problems. This paper outlines the anti-microfouling properties of some insolubilized quaternary ammonium salts (grafted onto a vinyl copolymer by means of a covalent non-hydrolyzable bond). After immersion times in sea-water up to 4 months, the microbial cover was limited to bacterial forms, without microalgae or cyanobacteria as observed on the untreated, or tin-salt painted surfaces. Bacteria are mostly on unicell forms and numerous areas appear free of any microorganisms. As microbiofouling is an obligate step to macrofouling, this unleachable antifouling treatment could result in a prolonged protection.  相似文献   

Aeromagnetic evidence for the rotation of Sardinia (Mediterranean Sea): comparison with the paleomagnetic measurements     

Armand Galdeano  Marcello Ciminale 《Earth and Planetary Science Letters》1987,82(1-2)

The aeromagnetic survey of Sardinia (western Mediterranean) delineated a large magnetic anomaly located in the western part of the island. The shape of the anomaly is improved and simplified by upward continuation, and modelling in terms of three-dimensional structure gives a westward remanent magnetization. Some tests have been carried out to suppress ambiguities on the magnetic dual aspect “magnetization distribution-shape of sources”. The optimal declination obtained after a few testings is 30° west which is ascribed to the rotation of Sardinia. This value confirms the results provided by paleomagnetic investigations and is significant because it characterizes a large and deep-rooted structure involved in the rotation of Sardinia. Our results thus illustrate another interesting application of aeromagnetic surveys.  相似文献   

Comparing the patterns of 20–70 days intraseasonal oscillations over Central Africa during the last three decades     

Alain Tchakoutio Sandjon  Armand Nzeukou  Clément Tchawoua  Brice Sonfack  Tengeleng Siddi 《Theoretical and Applied Climatology》2014,118(1-2):319-329

In this paper, we used the Outgoing Longwave Radiation (OLR) data to compare the intraseasonal atmospheric variability patterns over Central Africa, during the last three decades. The spectral analysis indicates that for the three decades, the intraseasonal variability is dominated by 20–80 days periods band with the center near 40–50 days. The results of Empirical Orthogonal Functions (EOFs) analysis have shown that the amount of variance explained by the three retained EOFs are 41.6 % for 1981–1990, 44.2 % for 1991–2000 and 42.6 % for 2001–2010. For the three decades, the three leading EOFs retained exhibit high spatial loadings over Northern Congo, Southern Ethiopia, and Southwestern Tanzania. The power spectra of the leading principal components have their peaks near 40 days for the three decades, indicating MJO signal. The PCs time series revealed that the amplitude of intraseasonal oscillations (ISO) globally decreases from decade to another. The plot of ISO and El Niño-Southern Oscillation (ENSO) indices revealed that the lowest values of ISO strength generally correspond to the relatively large values of ENSO indices and inversely. The mean ISO strength and ISO fluctuations were highest during 1981–1990, and this period also corresponds to the highest fluctuations of ENSO signal.  相似文献