Inversion of reflection seismograms by differential semblance analysis: algorithm structure and synthetic examples1     

William W. Symes  Michel Kern 《Geophysical Prospecting》1994,42(6):565-614

Seismograms predicted from acoustic or elastic earth models depend very non-linearly on the long wavelength components of velocity. This sensitive dependence demands the use of special variational principles in waveform-based inversion algorithms. The differential semblance variational principle is well-suited to velocity inversion by gradient methods, since its objective function is smooth and convex over a large range of velocity models. An extension of the adjoint state technique yields an accurate estimate of the differential semblance gradient. Non-linear conjugate gradient iteration is quite successful in locating the global differential semblance minimum, which is near the ordinary least-squares global minimum when coherent data noise is small. Several examples, based on the 2D primaries-only acoustic model, illustrate features of the method and its performance.  相似文献   

Seismic Anisotropy In the Crust At the Mid-Atlantic Plate Boundary In South-West Iceland   总被引：3，自引：0，他引：3  

William Menke  Bryndis Brandsdottir  Steinun Jakobsdottir  Ragnar Stefansson 《Geophysical Journal International》1994,119(3):783-790

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The “susceptibility factor” in the atmospheric response to periodic forcing     

William H. Campbell  Reid A. Bryson 《Journal of Earth System Science》1993,102(1):157-173

Evidence is presented of a periodic component in the inter-annual variability of precipitation and pressure data for India during June, the month of the onset of the Indian southwest monsoon. Two frequencies that explain a statistically significant percent of the variance in these data sets are the same as the two that explain most of the variance of the average monthly lunar tidal potential for June. Not only are the frequencies the same but they are also in phase which strongly suggests that lunar tides in the atmosphere do, in fact, produce an element of climatic variability. The amplitude of the atmospheric response to this periodic forcing was not constant in time but was found to be related to the long term change in northern hemispheric surface temperature. This susceptibility of the atmosphere to an external forcing results in a nonlinear relationship between forcing and response. As a result, nonlinear regression had to be used in order to adequately define the magnitude of the response at a given frequency. The ramifications of this nonlinear response are discussed. The nonlinear interaction of the northern hemisphere temperature and the 18.6 year lunar nodal cycle results in a modulation of the frequency which appears in a linear spectral analysis near 22 years. Thus, the 22-year cycle often found in meteorological data sets may instead be the result of the modulated nodal cycle.  相似文献   

Partitioning of platinum-group elements and Au in the Fe−Ni−Cu−S system: experiments on the fractional crystallization of sulfide melt   总被引：6，自引：0，他引：6  

Michael E. Fleet  Stephen L. Chryssoulis  William E. Stone  Christopher G. Weisener 《Contributions to Mineralogy and Petrology》1993,115(1):36-44

Partitioning of platinum-group elements (PGE) between sulfide liquid and monosulfide solid solution (mss) has been investigated by crystallizingmss from Fe–Ni–Cu sulfide liquid at 1,000–1,040° C, using bulk compositions and PGE contents typical of magmatic sulfides associated with mafic and ultramafic systems. Products were analyzedin situ for PGE and Au using SIMS. Sulfide liquid compositions were more Ni- and Cu-rich than coexistingmss. Liquid/mss partition coefficients are: Os-0.23±0.04, Ir-0.28±0.11, Ru-0.24±0.05, Rh-0.33±0.06, Pt-4.8±0.7, Pd-4.8±1.9, Au-11.4. Partitioning of PGE is independent of PGE concentration and Ni content in the composition range investigated. Additionally, Henry's law appears to be obeyed up to minor-element contents in the sulfide liquid andmss. Osmium, Ir, Ru, and Rh are compatible elements in the anhydrous Fe–Ni–Cu–S system, whereas Pt, Pd and Au are incompatible elements. These affinities correspond to the partitions of PGE between massive and Cu-rich magmatic sulfides. However, the detailed precious-metal compositions of the Cu-rich sulfides of mafic rock systems, disseminated ores of komatiites and Cu-rich assemblage of droplet ore from the Noril'sk-Talnakh deposits are not consistent with those expected for pristine fractionated sulfide liquids.  相似文献   

The heat capacity of hydrous cordierite above 295 K     

J. William Carey 《Physics and Chemistry of Minerals》1993,19(8):578-583

The heat capacity of synthetic hydrous cordierite (Mg₂Al₄Si₅O₁₈·nH₂O) has been determined by differential scanning calorimetry (DSC) from 295 to 425 K as a function of H₂O content. Six samples with H₂O contents ranging from 0 to 0.82 per formula unit were examined. The partial molar heat capacity of H₂O in cordierite over the measured temperature interval is independent of composition and temperature within experimental uncertainty and is equal to 43.3 ±0.8 J/mol/ K. This value exceeds the molar heat capacity of gaseous H₂O by 9.7 J/mol/K, but is significantly smaller than the heat capacity of H₂O in several zeolites and liquid H₂O. A statistical-mechanical model of the heat capacity of adsorbed gas species (Barrer 1978) is used to extrapolate the heat capacity of hydrous cordierite to temperatures greater than 425 K. In this model, the heat capacity of hydrous cordierite (Crd·nH₂O) is represented as follows: Cp(Crd · nH₂O) = Cp(Crd)+ n{Cp(H₂O, gas)+ R(gas constant)} (1) An examination of calorimetric data for hydrous beryl, analcime, mordenite, and clinoptilolite (Hemingway et al. 1986; Johnson et al. 1982, 1991, 1992) demonstrates the general applicability of the statistical-mechanical model for the extrapolation of heat capacity data of zeolitic minerals. The heat capacity data for cordierite are combined with the data of Carey and Navrotsky (1992) to obtain the molar enthalpy of formation and enthalpy of hydration of hydrous cordierite as a function of temperature.  相似文献   

The reconstruction of eighteenth century temperature records through the use of content analysis     

William R. Baron 《Climatic change》1982,4(4):385-398

The reconstruction of a temperature record for eighteenth century eastern Massachusetts is discussed. In addition to instrumental records diaries were analyzed in order to produce temperature indices. Reliability tests demonstrate that the methodology used is capable of replicating results regardless of changes in coders or intraregional variability in language. Validity tests, comparing diary reconstructions with instrumental records for the same period, produced positive results. A compilation of all climate related data shows the decades of the 1720's, 1750's, and 1760's were cool, while the 1770's and 1790's were warm.  相似文献   

Rhyodacites,andesites, ferro-basalts and ocean tholeiites from the galapagos spreading center     

Gary R. Byerly  William G. Melson  Peter R. Vogt 《Earth and Planetary Science Letters》1976,30(2):215-221

Volcanic rocks, dredged from depths greater than 1000 m on the Galapagos spreading center, show extreme chemical diversity, including rhyodacites, andesite, ferro-basalts, and low-K oceanic tholeiite. All samples have fresh glassy margins. The ferro-basalts contain up to 18.5% total iron as FeO and up to 3.75% TiO₂, while the oceanic tholeiites are as low as 0.02% K₂O. The ferro-basalts correlate with the previously proposed zone of high magnetic anomaly amplitudes which flank the Galapagos hot spot, and are consistent with a genesis by shallow fractional crystallization.  相似文献   

Co²⁺ as a chemical analogue for Fe²⁺ in high-temperature experiments in basaltic systems     

William E. Coons  John R. Holloway  Alexandra Navrotsky 《Earth and Planetary Science Letters》1976,30(2):303-308

High-temperature experiments on ferromagnesian compositions have been hampered by the rapid absorption of up to 95% of the original iron by platinum and 40% by silver-palladium capsules. Molybdenum or iron capsule materials can decrease or alleviate iron loss, but restrict oxygen fugacities to values near the iron-wustite buffer. Because Co²⁺ is stable at f_O2 =HM and because the solubility of Co in platinum in this range of f_O2 is ～0.05% at temperatures to 1350°C, its use as an analogue for Fe²⁺ is possible. In addition, experiments simulating various Fe²⁺ ratios can be easily performed by choosing appropriate Co²⁺/Fe³⁺ ratios. The cobalt phases produced possess brilliant and distinctive colors which are valuable aids in optical identification of minute phases. The cobalt analogue hypothesis was tested with atmospheric pressure experiments in air on the cobalt analogue of the 1921 Kilauea basalt at three simulated Fe²⁺/Fe³⁺ ratios. The results were compared with those of R.E.T. Hill (1969) for the natural 1921 basalt. The phase relations were the same, with the cobalt system stability fields systematically shifted by about +50°C. Microprobe analysis of olivines and the coexisting glasses indicate that the distribution of Co²⁺ between olivine and melt is independent of temperature and liquid composition. Although the analogue liquid composition differs from the equilibrium composition of the natural system, it may be corrected be employing distribution coefficients (K_D = 0.61 for the Co system; K_D = 0.33 for the Fe system) to closely approximate what the natural system would yield if iron loss did not occur.  相似文献   

Combined analysis and test of earthquake-resistant circuit breakers     

Edward G. Fischer  William M. Daube 《地震工程与结构动力学》1976,4(3):231-244

Following the severe earthquake damage at San Fernando in 1971, it became of technical and perhaps psychological importance to demonstrate that properly re-designed electrical equipment is able to withstand even worse transient vibration phenomena which can be produced in an earthquake simulator laboratory. This has been accomplished for one column of a 500 kV gas circuit breaker and the test results are used to qualify the much larger original 3-column assembly by means of a computer-aided structural analysis. Since the equipment exhibited some closely spaced, cross-coupled modes of vibration, a valuable comparison could be obtained between the effects produced by El Centro 1940 ground acceleration and those for a more purposeful sine beat vibration input. The latter can be adjusted to produce definite stresses and fatigue effects in specific parts of the equipment due to quasi-resonance response.  相似文献   

Petrology and geochemistry of plagiogranite in the Canyon Mountain ophiolite,Oregon     

David C. Gerlach  William P. Leeman  Hans G. Avé Lallemant 《Contributions to Mineralogy and Petrology》1981,77(1):82-92

Plagiogranites in the Canyon Mountain ophiolite, Oregon, include a wide range of rock types ranging from diorite to trondhjemite. The plagiogranites are mostly concentrated as an intrusive sill swarm at the top of a section of gabbroic cumulates. The plagiogranites are typically low in K₂O and high in Na₂O, and are enriched 10–20 times chondrites in REE, and overlap with abundances in basic rocks from Canyon Mountain. All samples of plagiogranite are relatively depleted in LREE, with more silicic samples characterized by a slightly lesser degree of LREE depletion. Total REE content is not consistently correlated with contents of major and other trace elements. Fractional crystallization of basaltic magma may give rise to plagiogranites; however this model applied to Canyon Mountain plagiogranites is discounted because of the significant volume of plagiogranites relative to basic rocks, and the complete overlap of REE abundances of the basic rocks and the plagiogranites. The latter is also a major reason for rejecting the hypothesis of silicate liquid immiscibility in the generation of the plagiogranites. Field observations coupled with major-element and trace element chemistry lend support to a model by which the plagiogranites were produced by partial melting of basic rocks under hydrous conditions. REE data for the plagiogranites were used in calculations to delimit source REE contents. Relevant parameters in the calculations were estimated from experimentally determined phase relations of basalt under hydrous conditions. The resulting calculated source patterns are similar to those of basic rocks in ophiolites and oceanic settings, and suggest boundary conditions for the model. Partial melting as suggested for the Canyon Mountain plagiogranites probably occurred at relatively shallow depths (i.e., total pressures less than 5 kb).  相似文献