140 research outputs found
Physique de lâintĂ©rieur de la Terre
Enseignement Cours â Les grands tremblements de terre Comprendre la physique du dĂ©roulement de la rupture dâun grand sĂ©isme â tel quâils se produisent dans les zones de subduction autour du Pacifique â, depuis sa phase prĂ©paratoire jusquâĂ ses effets destructeurs en champ proche ou lointain, est une question majeure dâintĂ©rĂȘt socioĂ©conomique. Depuis quelques dĂ©cennies, grĂące aux efforts importants dâinstrumentation sismique et gĂ©odĂ©sique (en particulier GPS) dans certaines zones concernĂ©es, e..
Colloque « Great Earthquakes: Observations and Modelling »
Rupture de surface sĂ©isme de M 7.8, Kunlun (Tibet), 2001. © Yann Klinger, IPG, Paris. Avec lâinstallation, depuis plusieurs dĂ©cennies, de nombreux rĂ©seaux dâobservation sismiques et gĂ©odĂ©siques au niveau global et dans certaines rĂ©gions exposĂ©es Ă de forts sĂ©ismes, telles le Japon ou le Chili, les progrĂšs technologiques de lâĂšre digitale ont permis dâacquĂ©rir des donnĂ©es de qualitĂ© remarquable sur plusieurs grands tremblements de terre rĂ©cents. Ce colloque international a rĂ©uni des spĂ©ciali..
LARGE SCALE THREE DIMENSIONAL P VELOCITY STRUCTURE BENEATH THE WESTERN U,S. AND THE LOST FARALLON PLATE
Abstract. The results of a recent large scale three-dimensional study of P velocity beneath North America are analyzed from the point of view of the search for the fossil Farallon plate in the mantle beneath the western edge of the North American continent
Inferring the thermochemical structure of the upper mantle from seismic data
We test a mineral physics model of the upper mantle against seismic observations. The model is based on current knowledge of material properties at high temperatures and pressures. In particular, elastic properties are computed with a recent self-consistent thermodynamic model, based on a six oxides (NCFMAS) system. We focus on average structure between 250 and 800 km. We invert normal modes eigenfrequencies and traveltimes to obtain best-fitting average thermal structures for various compositional profiles. The thermochemical structures are then used to predict long-period waveforms, SS precursors waveforms and radial profiles of attenuation. These examples show the potential of our procedure to refine the interpretation combining different data sets. We found that a mixture of MORB and Harzburgite, with the MORB component increasing with depth, is able to reproduce well all the seismic data for realistic thermal structures. If the proportions of MORB with depth do not change, unrealistic negative thermal gradients below 250 km would be necessary to explain the data. Equilibrium assemblages, such as pyrolite, cannot fit the seismic data. The elastic velocities predicted by the reference mineral physics model tested are too low at the top of the lower mantle, even for the fastest (and most depleted) composition, that is, harzburgite. An increase in VP of 1 per cent and in VS of 2 per cent improves the data fit significantly and is required to find models that fit both traveltimes and normal modes, indicating the need for further experimental measurements of these properties at the simultaneously elevated pressureâtemperature conditions of the lower mantle. Extending our procedure to other seismic and density data and interpreting the 3-D structure holds promise to further improve our knowledge of the thermochemical structure of the upper mantle. In addition, the same database of material properties can be used in dynamic models to test whether the thermochemical structure inferred from geophysical observations is consistent with the Earth's evolutio
Inferring the thermochemical structure of the upper mantle from seismic data
We test a mineral physics model of the upper mantle against seismic observations. The model is based on current knowledge of material properties at high temperatures and pressures. In particular, elastic properties are computed with a recent self-consistent thermodynamic model, based on a six oxides (NCFMAS) system. We focus on average structure between 250 and 800 km. We invert normal modes eigenfrequencies and traveltimes to obtain best-fitting average thermal structures for various compositional profiles. The thermochemical structures are then used to predict long-period waveforms, SS precursors waveforms and radial profiles of attenuation. These examples show the potential of our procedure to refine the interpretation combining different data sets.We found that a mixture of MORB and Harzburgite, with the MORB component increasing with depth, is able to reproduce well all the seismic data for realistic thermal structures. If the proportions of MORB with depth do not change, unrealistic negative thermal gradients below 250 km would be necessary to explain the data. Equilibrium assemblages, such as pyrolite, cannot fit the seismic data.The elastic velocities predicted by the reference mineral physics model tested are too low at the top of the lower mantle, even for the fastest (and most depleted) composition, that is, harzburgite. An increase in V P of 1 per cent and in V S of 2 per cent improves the data fit significantly and is required to find models that fit both traveltimes and normal modes, indicating the need for further experimental measurements of these properties at the simultaneously elevated pressureâtemperature conditions of the lower mantle.Extending our procedure to other seismic and density data and interpreting the 3-D structure holds promise to further improve our knowledge of the thermochemical structure of the upper mantle. In addition, the same database of material properties can be used in dynamic models to test whether the thermochemical structure inferred from geophysical observations is consistent with the Earth's evolution.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/78699/1/j.1365-246X.2009.04338.x.pd
A Plan for a Long-Term, Automated, Broadband Seismic Monitoring Network on the Global Seafloor
Establishing an extensive and highly durable, longâterm, seafloor network of autonomous broadband seismic stations to complement the landâbased Global Seismographic Network has been a goal of seismologists for decades. Seismic signals, chiefly the vibrations from earthquakes but also signals generated by storms and other environmental processes, have been processed from landâbased seismic stations to build intriguing but incomplete images of the Earthâs interior. Seismologists have mapped structures such as tectonic plates and other crustal remnants sinking deep into the mantle to obtain information on their chemical composition and physical state; but resolution of these structures from land stations is not globally uniform. Because the global surface is twoâthirds ocean, increasing the number of seismic stations located in the oceans is critical for better resolution of the Earthâs interior and tectonic structures. A recommendation for a longâterm seafloor seismic station pilot experiment is presented here. The overarching instrumentation goal of a pilot experiment is performance that will lead to the installation of a large number of longâterm autonomous oceanâbottom seismic stations. The payoff of a network of stations separated from one another by a few hundred kilometers under the global oceans would be greatly refined resolution of the Earthâs interior at all depths. A second prime result would be enriched understanding of largeâearthquake rupture processes in both oceanic and continental plates. The experiment would take advantage of newly available technologies such as robotic wave gliders that put an affordable autonomous prototype within reach. These technologies would allow data to be relayed to satellites from seismometers that are deployed on the seafloor with longâlasting, rechargeable batteries. Two regions are presented as promising arenas for such a prototype seafloor seismic station. One site is the central North Atlantic Ocean, and the other highâinterest locale is the central South Pacific Ocean
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The Aromatase Gene (CYP19A1) Variants and Circulating Hepatocyte Growth Factor in Postmenopausal Women
Background: Estrogen and androgen have been linked to the regulation of circulating hepatocyte growth factor (HGF), an adipose tissue-derived cytokine. It is possible that the CYP19A1 gene which alters sex hormones production may influence HGF levels. We examined the association between the CYP19A1 gene variants and plasma HGF concentrations. Design We evaluated 45 common and putative functional variants of CYP19A1 and circulating levels of HGF among 260 postmenopausal women who later developed colorectal cancer from the Women's Health Initiative Observational Cohort. As the distribution of HGF levels was highly skewed, we transformed HGF concentrations for all women into a log-, ranked-, or normal score-scale value. Multiple linear regression with adjustment for age was used to evaluate the associations. Results: We observed an association between the rs7172156, rs1008805, rs6493494, rs749292, and rs11636639 variants and HGF levels in ranked and normal score scales (corrected p values â€0.02), although the association of these 5 SNPs with log-scale HGF was not significant (corrected p values â„0.16). The associations remained unchanged after additional adjustment for hormone therapy use and estradiol levels. These 5 SNPs, which were in linkage disequilibrium (pairwise DâČâ„97%, r2â„56%), constituted a block with 2 common haplotypes accounting for 82% frequency. The most common haplotype, TCCCA, was associated with lower ranked- or normal score-transformed HGF levels (corrected p values â€0.001), whereas the second most common haplotype, CTTCA, was associated with higher ranked- or normal score-transformed HGF levels (corrected p values â€0.02). Conclusion: Our findings of a potential association between the CYP19A1 variants and circulating HGF levels warrant confirmation in studies with larger sample size
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