Large-scale coherent anisotropy of upper mantle beneath the Italian peninsula comparing quasi-Love waves and SKS splitting     

《Journal of Geodynamics》2014

We document quantitatively observations of quasi-Love waves obtained at permanent (Italian National Seismic Network) and temporary seismic stations deployed in Italy between 2003 and 2006 (Retreat, CAT/SCAN projects). We analyzed large earthquakes with source parameters that favor quasi-Love wave generation within this time-span, including the Sumatra–Andaman earthquake of 12/26/04. The presence or the absence of the quasi-Love phase is compared to the smoothed anisotropic pattern defined by the numerous SKS splitting measurements obtained in peninsular Italy, and to the Italian upper mantle structure as defined by seismic tomography. The large-scale anisotropic features, responsible for shear-wave splitting and documented also by Pn and surface-wave anisotropy, generally display the correct geometry to explain the scattered quasi-Love waves. Quasi-Love observations do not demand a tilted-axis anisotropic geometry. We argue instead for anisotropy with laterally-variable horizontal symmetry axis in the upper mantle below the Italian peninsula.  相似文献   

The origin of the moon and the single-impact hypothesis I     

《Icarus》1986,66(3):515-535

Recently the single-impact hypothesis for forming the Moon has gained some favorable attention. We present in this paper a series of three-dimensional numerical simulations of an impact between the protoearth and an object about 0.1 of its mass. For computational convenience both objects were assumed to be composed of granite. We studied the effects on the outcome of the collision of varying the impact parameter, the initial internal energy, and the relative velocity. The results show that if the impact parameter is large enough so that the center of the impactor approximately grazes the limb of the protoearth, the impactor is not completely destroyed; part of it forms a clump in a large elliptical orbit about the Earth. This clump does not collide with the Earth, since the effects, first, of vapor pressure gradients during the impact, and later, of angular momentum transfer due to the rotation of the deformed Earth, have modified the ballistic trajectory. However, since the orbit of the clump comes close to the Earth (within the Roche limit) the clump will be destroyed and spread out to form a disk around the Earth. The amount of angular momentum in the Earth-Moon system thus obtained tends to fall short of the observed amount; this deficiency would be eliminated if the mass of the impactor were somewhat greater than the one assumed here. The scenario for making the Moon from a single-impact event is supported by these simulations.  相似文献   

Efficient clustered server-side data analysis workflows using SWAMP     

Daniel L. Wang  Charles S. Zender  Stephen F. Jenks 《Earth Science Informatics》2009,2(3):141-155

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The formation and alteration of the Renazzo-like carbonaceous chondrites I: Implications of bulk-oxygen isotopic composition     

Devin L. Schrader  Ian A. Franchi  Richard C. Greenwood  Jenny M. Gibson 《Geochimica et cosmochimica acta》2011,75(1):308-325

To better understand the role of aqueous alteration on the CR chondrite parent asteroid, a whole-rock oxygen isotopic study of 20 meteorites classified as Renazzo-like carbonaceous chondrites (CR) was conducted. The CR chondrites analyzed for their oxygen isotopes were Dhofar 1432, Elephant Moraine (EET) 87770, EET 92042, EET 96259, Gao-Guenie (b), Graves Nunataks (GRA) 95229, GRA 06100, Grosvenor Mountains (GRO) 95577, GRO 03116, LaPaz Ice Field (LAP) 02342, LAP 04720, Meteorite Hills (MET) 00426, North West Africa (NWA) 801, Pecora Escarpment (PCA) 91082, Queen Alexandra Range (QUE) 94603, QUE 99177, and Yamato-793495 (Y-793495). Three of the meteorites, Asuka-881595 (A-881595), GRA 98025, and MET 01017, were found not to be CR chondrites. The remaining samples concur petrographically and with the well-established oxygen-isotope mixing line for the CR chondrites. Their position along this mixing line is controlled both by the primary oxygen-isotopic composition of their individual components and their relative degree of aqueous alteration. Combined with literature data and that of this study, we recommend the slope for the CR-mixing line to be 0.70 ± 0.04 (2σ), with a δ¹⁷O-intercept of −2.23 ± 0.14 (2σ).Thin sections of Al Rais, Shi?r 033, Renazzo, and all but 3 samples analyzed for oxygen isotopes were studied petrographically. The abundance of individual components is heterogeneous among the CR chondrites, but FeO-poor chondrules and matrix are the most abundant constituents and therefore, dominate the whole-rock isotopic composition. The potential accreted ice abundance, physico-chemical conditions of aqueous alteration (e.g. temperature and composition of the fluid) and its duration control the degree of alteration of individual CR chondrites. Combined with literature data, we suggest that LAP 02342 was exposed to lower temperature fluid during alteration than GRA 95229. With only two falls, terrestrial alteration of the CR chondrites complicates the interpretation of their whole rock isotopic composition, particularly in the most aqueously altered samples, and those with relatively higher matrix abundances. We report that QUE 99177 is the isotopically lightest whole rock CR chondrite known (δ¹⁸O = −2.29‰, δ¹⁷O = −4.08‰), possibly due to isotopically light unaltered matrix; which shows that the anhydrous component of the CR chondrites is isotopically lighter than previously thought. Although it experienced aqueous alteration, QUE 99177 provides the best approximation of the pristine CR-chondrite parent body’s oxygen-isotopic composition, before aqueous alteration took place. Using this value as a new upper limit on the anhydrous component of the CR chondrites, water/rock ratios were recalculated and found to be higher than previously thought; ratios now range from 0.281 to 1.157. We also find that, according to their oxygen isotopes, a large number of CR chondrites appear to be minimally aqueously altered; although sample heterogeneity complicates this interpretation.  相似文献   

Quantitative visualization of geophysical flows using low-cost oblique digital time-lapse imaging     

Pawlowicz  R. 《Oceanic Engineering, IEEE Journal of》2003,28(4):699-710

Estuaries and coastal waters are regions where many different important physical processes can be found. Although the physical scale of these processes is often relatively small, their time scales are correspondingly rapid and aliasing is usually a problem in sampling programs. There can be significant spatial variations in mixing and flow patterns, which are usually learned only through long experience in a particular region. Observational and interpretation difficulties might be significantly simplified with a simple remote sensing tool to be used in conjunction with standard techniques. Here, the use of digital time-lapse photography at highly oblique angles as a tool for flow visualization is discussed. The interaction of surface waves with slicks and internal motions can cause apparent changes in the shade and color of water at shallow angles in a way not apparent in downlooking views. The use of time-lapse techniques allows us to isolate time scales of interest and, by "speeding up" low-frequency motions, causes them to become more apparent to the eye. A cheap and portable system based on commercially available equipment is described and various advantages and shortcomings are discussed. Results are shown to illustrate the utility of the observational system.  相似文献   

Analytical optimization of a DInSAR and GPS dataset for derivation of three-dimensional surface motion   总被引：2，自引：0，他引：2  

Samsonov  S. Tiampo  K. 《Geoscience and Remote Sensing Letters, IEEE》2006,3(1):107-111

A revised method for derivation of three-dimensional surface motions maps from sparse global positioning system (GPS) measurements and two differential interferometric synthetic aperture radar (DInSAR) interferograms based on a random field theory and Gibbs-Markov random fields equivalency within Bayesian statistical framework is proposed. It is shown that the Gibbs energy function can be optimized analytically in the absence of a neighboring relationship between sites of a regular lattice. Because the problem is well posed, its solution is unique and stable, and additional regularization in the form of smoothness is not required. The proposed algorithm is simple in realization, does not require extensive computer power, and is very quick in execution. The results of inverse computer modeling are presented and show a drastic improvement of accuracy when both GPS and DInSAR data are used.  相似文献   

Reductive deposition of graphite at lithological margins in East Central Vermont: a Sr, C and O isotope study   总被引：3，自引：0，他引：3  

K. A. Evans  M. J. Bickle  A. D. L. Skelton  M. Hall  H. Chapman 《Journal of Metamorphic Geology》2002,20(8):781-798

O, Sr and C isotopes from east‐central Vermont are used to provide information on the timing and volume of metamorphic fluid flow. The results are then used to assess the evidence for redox transformations between C species. Oxygen profiles are homogenised on a metre scale; comparison with Sr isotopes suggest that O alteration may have occurred over a significantly larger timescale than that of Sr, possibly because O was modified during dewatering and diagenesis in addition to the high temperature alteration recorded by strontium. Sr isotope distributions are consistent with cross‐layer fluid fluxes of 10⁴?10⁶ moles m^?2; absolute values depend on the Sr fluid‐rock distribution coefficient which is poorly known; however, reaction progress constraints suggest that fluxes were towards the lower end of this range. High δ¹³C values observed at lithological boundaries cannot be explained by volume loss or closed system processes and are taken to indicate reductive precipitation of graphite as a result of mixing between CO₂ and CH₄‐bearing fluids. Mass balance calculations indicate that redox reactions occurring under metamorphic conditions convert a minimum of 10% of the CO₂ released from limestones into graphite, thus providing a potentially important control on the average residence time of C within the crust with implications for C cycling models.  相似文献   

Stochastic modeling of seafloor morphology; Resolution oftopographic parameters by sea beam data     

Goff  J.A. Jordan  T.H. 《Oceanic Engineering, IEEE Journal of》1989,14(4):326-337

The authors explore the resolving power of an inversion algorithm which estimates five parameters of the seafloor covariance function from a single swath of multibeam echosounding data. The resolving power is evaluated as a function of the swath length, the orientation of ship track with respect to topographic grain, and the response width of the sounding system. The analysis is conducted by inverting sets of synthetic data with known statistics. The mean and standard deviation of the inverted parameters can be directly compared with the input parameters and the standard errors output from the inversion. Experiments show that resolution of the covariance parameters is strongly dependent on the number of characteristic lengths which are sampled. Root-mean-square seafloor height can be estimated to within ~15%, and anisotropic orientation to within ~5% (for a strong lineation), using track lengths as short as three characteristic lengths  相似文献   

Travel times and amplitudes of waves in central asia—Theory and experiments     

A. S. Alekseev  I. L. Nersesov 《Studia Geophysica et Geodaetica》1966,10(2):172-176

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