Caracas, Venezuela, Site Effect Determination with Microtremors   总被引：1，自引：0，他引：1  

A.-M. Duval  S. Vidal  J.-P. Méneroud  A. Singer  F. De Santis  C. Ramos  G. Romero  R. Rodriguez  A. Pernia  N. Reyes  C. Griman 《Pure and Applied Geophysics》2001,158(12):2513-2523

—?Caracas 1967 earthquake caused heavy damage to multi-story buildings. In 1995, 184 microtremor measurement points were performed over the city. The measurement grid was more or less dense and covered the main part of the alluvial basin as well as surrounding rock basement. For each point, the horizontal record spectrum was divided by the vertical one (H/V ratio). Subsequently, the strongest value (Ao) of this ratio in a given frequency band was kept, as well as the frequency (Fo) where it occurred. Spatial interpolations of Ao and Fo were performed among all points of Palos Grandes district. A map was plotted representing a single surface where Ao is relief and Fo is represented by grey gradation. An alluvion thickness (H) map can be compared with this result. Damaged buildings are located on the same map. Fo decreases until 0.6?Hz when alluvion thickness (H) increases. Fo values fit with frequencies previously predicted from computation and with 1967 earthquake observations. Moreover, interpolation surfaces show that amplification (Ao) of H/V on microtremor is quite low above rock but is high on the south part of the basin. The maximum occurs over the non-urbanized zone. However the other area, where Ao is higher than 5, roughly corresponds to the location of the four collapsed buildings. Furthermore, the estimated natural frequency of these buildings was around Fo. Graphics showing H, Fo and Ao evolution through the basin were composed. Links between all these values are noticeable. Fo is claimed to be very similar to the resonance frequency of soil. As for Ao, it could be a fairly relevant sign of damage seriousness. Microtremor technique is an economic tool and it allows measurement grid as dense as desired. H/V ratio processing followed by interpolation of maximum values provides precise and useful information about expected site effect.  相似文献   

The spray contribution to net evaporation from the sea: A review of recent progress   总被引：6，自引：0，他引：6  

Edgar L Andreas  James B. Edson  Edward C. Monahan  Mathieu P. Rouault  Stuart D. Smith 《Boundary-Layer Meteorology》1995,72(1-2):3-52

The part that sea spray plays in the air-sea transfer of heat and moisture has been a controversial question for the last two decades. With general circulation models (GCMs) suggesting that perturbations in the Earth's surface heat budget of only a few W m^–2 can initiate major climatic variations, it is crucial that we identify and quantify all the terms in that heat budget. Thus, here we review recent work on how sea spray contributes to the sea surface heat and moisture budgets. In the presence of spray, the near-surface atmosphere is characterized by a droplet evaporation layer (DEL) with a height that scales with the significant-wave amplitude. The majority of spray transfer processes occur within this layer. As a result, the DEL is cooler and more moist than the atmospheric surface layer would be under identical conditions but without the spray. Also, because the spray in the DEL provides elevated sources and sinks for heat and moisture, the vertical heat fluxes are no longer constant with height. We use Eulerian and Lagrangian models and a simple analytical model to study the processes important in spray droplet dispersion and evaporation within this DEL. These models all point to the conclusion that, in high winds (above about 15 m/s), sea spray begins to contribute significantly to the air-sea fluxes of heat and moisture. For example, we estimate that, in a 20-m/s wind, with an air temperature of 20°C, a sea surface temperature of 22°C, and a relative humidity of 80%, the latent and sensible heat fluxes resulting from the spray alone will have magnitudes of order 150 and 15 W/m², respectively, in the DEL. Finally, we speculate on what fraction of these fluxes rise out of the DEL and, thus, become available to the entire marine boundary layer.  相似文献   

Thermodynamic properties of the forsterite-fayalite (Mg2SiO4-Fe2SiO4) solid solution. determination of heat of formation     

P. Thierry  C. Chatillon-Colinet  J. C. Mathieu  J. R. Regnard  J. Amossé 《Physics and Chemistry of Minerals》1981,7(1):43-46

A high temperature calorimetric solution method involving the use of a sodium and lithium metaborate (NaBO₂+LiBO₂) molten bath at 1,180 K, has been developed in order to measure the enthalpy of formation of the forsterite-fayalite (Mg₂SiO₄-Fe₂SiO₄) system. The samples used for these measurements have been obtained by synthesis. They have been carefully controlled by chemical and X-ray analysis and Mössbauer spectroscopy. The results obtained for forsterite and fayalite agree closely with the data commonly found in the literature. Owing to the uncertainty of the experimental results, it is not possible to determine conclusively whether an enthalpy of mixing exists in this system.  相似文献   

²²⁶Ra and²²²Rn contents of Galapagos Rift hydrothermal waters —the importance of low-temperature interactions with crustal rocks     

Jack Dymond  Richard Cobler  Louis Gordon  Pierre Biscaye  Guy Mathieu 《Earth and Planetary Science Letters》1983,64(3):417-429

Hydrothermal waters collected by “Alvin” from the Galapagos Spreading Center are enriched in²²²Rn by factors of 50–200 over bottom waters. The²²⁶Ra in the same samples, however, is enriched by less than a factor of four over bottom waters. Enrichments of²²²Rn result primarily from α-recoil from rock surfaces while²²⁶Ra enrichments are dominantly produced by high-temperature alteration of cooling ridge volcanics. The abundances of both nuclides exhibit positive correlations with temperature. The data extrapolate to bottom water temperatures and compositions, demonstrating the importance of seawater mixing. Different vents, however, have different mixing lines, and vents with high²²²Rn have low²²⁶Ra. We propose these patterns result from variations in the extent of low-temperature crustal interaction with the hydrothermal fluids. Low-temperature crustal waters can maintain high steady state²²²Rn contents due to the α-recoil additions to the fluids. The²²⁶Ra, however, is strongly adsorbed at low-temperatures resulting in low concentrations of this nuclide in low-temperature crustal waters. Thus, physical mixing of a crustal water component with hydrothermal waters or variable crustal path lengths of the hydrothermal fluids can account for the variable mixing lines and²²²Rn/²²⁶Ra values of the hot springs.The²²²Rn/²²⁶Ra value appears to be a sensitive indicator of low-temperature crustal interaction. Values > 100 have experienced extensive crustal interaction and are indicative of diffuse hydrothermal flow. Values between 1 and 10 are indicative of primary hydrothermal fluids which have not experienced significant interaction with the crust. Values of²²²Rn/²²⁶Ra between 10³ and 10⁴ are indicative of interaction of the hydrothermal fluids with sediments. Such values are observed in water samples from the Galapagos hydrothermal mounds.  相似文献   

Mesquite (Prosopis glandulosa) germination and survival in black-grama (Bouteloua eriopoda) grassland: relations between microsite and heteromyid rodent (Dipodomys spp.) impact     

B.D. Duval  E. Jackson  W.G. Whitford   《Journal of Arid Environments》2005,62(4):541-554

Prosopis pallida H.B.K. is one of the most economically and ecologically important tree species in the arid and semi-arid lands of the American continent. Sections of P. pallida were used to describe its wood anatomy and to determine whether annual rings were visible or not. Results showed that P. pallida has well-differentiated annual growth rings and is therefore suitable for dendrochronological studies. Tree ring chronologies correlate well with precipitation events related to El Niño Southern Oscillation phases. A master chronology for the northern area of Peru was built with these data, and some physiological derivations from the anatomy of P. pallida wood are discussed.  相似文献   

Variations in the Earth's gravity field caused by torsional oscillations in the core     

Mathieu Dumberry  Jeremy Bloxham 《Geophysical Journal International》2004,159(2):417-434

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Azimuthal flows in the Earth's core and changes in length of day at millennial timescales     

Mathieu Dumberry  Jeremy Bloxham 《Geophysical Journal International》2006,165(1):32-46

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Genetic differentiation ofNiphargus rhenorhodanensis (Amphipoda) from interstitial and karst environments     

Jacques Mathieu  Fabrice Jeannerod  Frédéric Hervant  Thomas C. Kane 《Aquatic Sciences - Research Across Boundaries》1997,59(1):39-47

Electrophoretic variation in proteins encoded by seven presumptive gene loci was analyzed in four populations of the stygobiont amphipodNiphargus rhenorhodanensis. The four populations occur in different habitats, including one in drainage canals, another from sediments of the Ain River, a tributary of the Rhône River, and the remaining two occur in a karstic massif (Dorvan, Ain, France) in the epikarstic and at the base level of the massif, respectively. Six of the seven loci were polymorphic within or among populations, with as many as three electromorphs segregating at the most variable loci. Significant deficiencies in the frequency of heterozygotes were common. Genetic divergence between the two populations of the Dorvan Massif and between the two of the Ain River (forest and sediment habitats) was large. This was highly unexpected, particularly in the case of the two hydrologically connected populations of the Dorvan Massif. It is suggested that either low migration rates or the presence of ecological barriers to gene flow may result in strong genetic differention among local populations ofNiphargus.  相似文献   

The radiocarbon budget for Mono Lake: an unsolved mystery     

Wallace S. Broecker  Rik Wanninkhof  Guy Mathieu  Tsung-Hung Peng  Scott Stine  Steve Robinson  Andy Herczeg  Minze Stuiver 《Earth and Planetary Science Letters》1988,88(1-2)

Since 1957 the ¹⁴C/C ratio of the dissolved inorganic carbon in Mono Lake has risen by about 60‰. The magnitude of this increase is about four times larger than that expected from the invasion of bomb-produced¹⁴C from the atmosphere. We have eliminated the following explanations: (1) measurement error, (2) an unusually high physical exchange rate for non-reactive gases, (3) inorganic enhancement of the CO₂ exchange rate, and (4) biological enhancement of the CO₂ exchange rate. Clandestine disposal of waste radiocarbon remains a dark-horse explanation.In the course of our investigations we have uncovered evidence for at least one episodic input of radiocarbon-free carbon to the lake over the last 1000 years. We speculate that this injection was related to a hydrothermal event resulting from sublacustrine volcanic activity.  相似文献   

Coastal conglomerates around the Hadjer el Khamis inselbergs (western Chad,central Africa): new evidence for Lake Mega‐Chad episodes     

Mathieu Schuster  Philippe Duringer  Jean‐Francois Ghienne  Patrick Vignaud  Alain Beauvilain  Hassan Taisso Mackaye  Michel Brunet 《地球表面变化过程与地形》2003,28(10):1059-1069

This paper reports on a study dealing with the rhyolitic inselbergs of Hadjer el Khamis that formed palaeoislands during Lake Mega‐Chad events. Field observations have shown that: (1) conglomeratic patches of immature to mature clasts are preserved at the feet of the Hadjer el Khamis inselbergs; (2) in cross‐section, their pro?le reveals a well de?ned cliff–platform junction at a constant elevation (325 m). The monolithological clasts show all degrees of roundness, from angular cobbles to well rounded pebbles. This wide range of maturity suggests a coastal origin for these cobbles. The system was permanently fed with angular clasts, which were progressively worn by waves. Cobbles that were wave‐worked for the longest time are the best rounded. The cliff–platform junction is the result of erosion by waves, which attacked and undercut the inselberg cliffs during Lake Mega‐Chad events. Asymmetrical erosion pro?les moreover suggest a wind regime dominated by SW to NE oriented winds. These interpretations have two implications. The elevation of the cliff–platform junction is an indication of the highest water level of Lake Mega‐Chad at 320–325 m, which is in agreement with other observations elsewhere in the basin. The SW to NE oriented winds show that monsoon‐related winds were prevalent during Lake Mega‐Chad events, suggesting the Inter‐Tropical Convergence Zone was located higher in latitude than today. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献