Use of stable carbon isotope compositions of pyrolytically derived methane as maturity indices for carbonaceous materials     

H.Moses Chung  William M. Sackett 《Geochimica et cosmochimica acta》1979,43(12):1979-1988

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An observational study of the influence of large-scale mountains on air flow and lee cyclogenesis     

Yong-Seung Chung 《Meteorology and Atmospheric Physics》1977,26(2-3):109-126

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Pn velocity and partial melting—discussion     

D.H. Chung 《Tectonophysics》1977,42(1):T35-T42

The seismologically observed P_n velocity anomalies in the conterminous United States are restricted to the lithosphere, but the observed teleseismic delay-time variations are due principally to the regional variations in the physical state (i.e., thickness of lowvelocity zone and/or percent melt, etc.) of the asthenosphere. The observed low P_n velocity has been attributed to partial melting in the upper mantle, but it is shown that the partial-melting model alone cannot explain the seismologically observed Pn velocities in such an anomalous region as the Basin and Range Province. The present structure of the Basin and Range Province is possibly a result of rifting in the western conterminous United States; under it there may lie a mixed structure of old crust and mantle materials. The low-velocity zone under the Basin and Range Province would then be caused by downward chemical transition from the sub-Moho pyrolitic mantle material into a plagioclase-rich ophiolitic (old oceanic crust and upper mantle) composition and associated meltingand then into a peridotitic composition at the bottom of the lowvelocity zone. This mixed material model, with partial melting, would explain the low P_n velocity and low seismic Q in the region, as well as other geophysical observations.  相似文献   

Excess²²²Rn and the benthic boundary layer in the western and southern Indian Ocean     

Y. Chung  K. Kim 《Earth and Planetary Science Letters》1980,49(2):351-359

We present 9 bottom²²²Rn profiles measured from the western and southern Indian Ocean during the 1977–1978 GEOSECS expedition. These profiles can be grouped into three cypes: one-layer, two-layer, and irregular types. The one-layer profiles with quasi-exponential distributions allow one to estimate the apparent vertical eddy diffusivity,K_v, with a simple model. The two-layer profiles show that there is a benthic boundary layer of the order of 50–100 m in which the excess²²²Rn distribution shows a vertical gradient much smaller than that of the layer immediately above. Within the boundary layer, the STD potential temperature (θ) and density(σ₄) profiles are practically constant, and theK_v values are of the order of 1000 cm²/s. The STD profiles for the water column above the boundary layer show gradients of increasing stability, and theK_v values are of the order of 100 cm²/s. Modeling of the Rn data in the water column above the boundary layer indicates that there is a transition layer which effectively reduces the penetration of excess Rn from the benthic boundary layer into the upper layer.Sarmiento et al. [10] have shown that the buoyancy gradient or stability is inversely correlated with the apparent vertical eddy diffusivity, and the resulting buoyancy flux is fairly uniform, ranging from 1 to 14 × 10^?6 cm²/s³ in the Atlantic and Pacific Oceans. However, Sarmiento et al. [11] show that a much higher buoyancy flux is associated with an intensified flow of the bottom water through a passage. In the Indian Ocean basins, we have found that the buoyancy flux has a comparable range (3–14 × 10^?6 cm²/s³), except for a couple of stations where both stability and apparent vertical diffusivity are higher, resulting in a much higher buoyancy flux, probably indicative of rapid bottom water flow.  相似文献   

²²⁶Ra and²¹⁰Pb in the Weddell Sea     

Y. Chung  M.D. Applequist 《Earth and Planetary Science Letters》1980,49(2):401-410

²²⁶Ra and²¹⁰Pb were measured in sections and profiles collected in the Weddell Sea during the International Weddell Sea Oceanographic Expedition in 1973. The results can be correlated with the circulation and mixing schemes deduced from hydrographic observations. Along the surface cyclonic gyre the Ra activities are fairly uniform at about 17 dpm/100 kg, quite similar to those of the Circumpolar surface water south of the Antarctic Convergence. The²¹⁰Pb activities in the northern flank of the gyre, probably influenced by the high²¹⁰Pb-bearing Circumpolar Deep Water in the north, are as high as 12 dpm/100 kg. At the central gyre and its southern flank, the surface water²¹⁰Pb activities are about 7 dpm/100 kg. The warmer surface water at the central gyre has a Ra activity of about 19 dpm/100 kg, slightly higher than the colder surface water at the flanks. Thus lower²¹⁰Pb/²²⁶Ra activity ratios are observed in the central gyre, and higher ratios in its flanks. Similar relationships between Ra and Pb are noted in the Weddell Sea Bottom Water (WSBW): lower Pb associated with higher Ra in the center; higher Pb with slightly lower Ra in the flanks.Vertical profiles along the cyclonic gyre show lower Ra and Pb activities in the southwestern Weddell Basin where lower temperature and lower silicate are observed. Similar to Ba, both Ra and Si are non-conservative in the Weddell Sea, with significant input from the bottom sediments and particulate dissolution during subsurface mixing.Each water mass or type in the Weddell Sea is well characterized by its Ra content, but not well by its Pb content. Ra and Si are crudely correlated with a slope of about 7 × 10^?4 dpm Ra per μmole of Si. The fact that the WSBW values fall on the slope suggests that the net input rate for Ra (corrected for the decay rate) is proportional to that of Si. The linear extrapolation to zero Si gives a Ra value of 13 dpm/100 kg. These relationships are quite similar to those observed in the Circumpolar waters.  相似文献   

Variation of seismic source parameters and stress drops within a descending slab and its implications in plate mechanics   总被引：1，自引：0，他引：1  

Wai-Ying Chung  Hiroo Kanamori 《Physics of the Earth and Planetary Interiors》1980,23(2):134-159

A least-squares searching technique has been developed to estimate the source dimensions of intermediate and deep focus earthquakes using azimuthal variations of body wave pulse-widths. With this method and also amplitude data, modes of rupture propagation, seismic moments, and stress drops of 17 intermediate and deep focus earthquakes in the Tonga-Kermadec region have been determined in order to investigate variations in source properties and the state of stress within the descending slab there. Three different modes of rupture; unilateral, bilateral, and circular faults, are compared and tested against observations. Results indicate that the unilateral fault is the best model for most of the earthquakes studied. Stress drops of the 17 events vary within a very large range, from 20 bar to about 4.6 kbar, and change significantly with depth. The magnitude of stress drops for depths between 220 and 430 km is very much higher than at shallower depths. This change in stress drop magnitude at about 220 km-depth seems to reflect a change in material properties both in the mantle and within the slab. Two regions of high stress drop are observed at depths of about 360 and 640 km. A relative minimum of stress drop is found at about 450–560 km where the earthquake frequency is particularly high. Earthquakes at the northern end to the Tonga arc, where the Benioff zone is laterally bent, show systematically higher stress drops than other events at comparable depths, but away from the bend. Also, events in regions of low seismicity appear to have higher stress drops than those in regions of high seismicity. The upper bound of seismic efficiency is found to decrease with depth, implying an increase of frictional force with depth at the earthquake source.  相似文献   

General relationships among sound speeds: I. New experimental information     

D.H. Chung 《Physics of the Earth and Planetary Interiors》1974,8(2):113-120

New ultrasonic data on some crystal structures important in mantle mineralogy are presented for compounds of Mg₂GeO₄, Fe₂GeO₄ and Fe₂SiO₄, both in olivine and spinel structures, and of GeO₂, SnO₂ and SiO₂ in the rutile structure, as their elastic parameters were determined by a powder—matrix method. With these new elasticity data, a power law for the velocity-density relationship arising from lattice dynamics is examined. Specific conclusions made are: (1) ultrasonic measurements on germanate compounds become very useful for estimating the elastic parameters of their silicate analogs: (2) the power law describes the velocity-density relationship for high-pressure polymorphs better than Birch's linear law: and (3) the power law is useful in our study of the elasticity and constitution of the elasticity and constitution of the deep interiors of the earth and other planets.  相似文献   

A study of phase transformation in hedenbergite to 40 GPa at ∼1200° C     

Young-Ho Kim  Li Chung Ming  Murli H. Manghnani 《Physics and Chemistry of Minerals》1989,16(8):757-762

Phase transformations in a natural sample of hedenbergite ((Ca_0.93Fe_0.61Mn_0.34Mg_0.08Na_0.01Zn_0.02Al_0.003)Si₂O₆) have been studied by X-ray diffraction up to 40 GPa at ∼ 1200°C in a diamond anvil cell interfaced with a laser heating system. The starting hedenbergite phase decomposed into a garnet plus γ-spinel and stishovite at ∼ 14 GPa; then into garnet plus stishovite and wüstite at ∼ 18 GPa; and finally into perovskite plus stishovite and wüstite at pressures higher than ∼ 24 GPa. On decompression to 0.1 MPa, all the high pressure phases are retained except for the cubic perovskite, which reverts back into the ɛ-CaSiO₃ phase, in accordance with previous reports. Energy-dispersive SEM analyses show that the garnet is present as a calcium-rich ABO ₃-type phase. As no garnet phase has been previously observed either in pure CaSiO₃ or in pure CaMgSi₂O₆, it appears that the observed calcium-rich garnet phase has been stabilized by the presence of other cations such as the Na⁺, Zn²⁺, Mn²⁺, Fe²⁺, Mn³⁺, Fe³⁺ and Al³⁺.  相似文献   

Environmental control of carbon isotope variations in Pennsylvania black-shale sequences, Midcontinent, U.S.A.     

Lloyd M Wenger  Donald R Baker  H.Moses Chung  Thane H McCulloh 《Organic Geochemistry》1988,13(4-6)

A reversal of the conventional carbon isotope relationship, “terrestrial-lighter-than-marine” organic matter, has been documented for two Pennsylvanian (Desmoinesian) cyclothemic sequence cores from the Midcontinent craton of the central United States. “Deep” water organic-rich phosphatic black shales contain a significant proportion of algal-derived marine organic matter (as indicated by organic petrography, Rock-Eval hydrogen index and ratios) and display the lightest δ¹³C-values (max −27.80‰ for kerogen) while shallower water, more oxic facies (e.g. fossiliferous shales and limestones) contain dominantly terrestrial organic matter and have heavier δ¹³C_kerogen-values (to −22.87‰ for a stratigraphically adjacent coal). δ¹³C-values for extract fractions were relatively homogeneous for the organic-rich black shales with the lightest fraction (often the aromatics) being only 1‰, or less, more negative than the kerogen. Differences between extract fractions and kerogens were much greater for oxic facies and coals (e.g. saturates nearly 5‰ lighter than the kerogen).A proposed depositional model for the black shales calls upon a large influx of nutrients and humic detritus to the marine environment from the laterally adjacent, extremely widespread Pennsylvanian (peat) swamps which were rapidly submerged by transgression of the epicontinental seas. In this setting marine organisms drew upon a CO₂-reservoir which was in a state of disequilibrium with the atmosphere, being affected by isotopically light “recycled-CO₂” derived from the decomposition of peaty material in the water column and possibly from the anoxic diagenesis of organic matter in the sediments.  相似文献   

Predicting landslides for risk analysis — Spatial models tested by a cross-validation technique   总被引：3，自引：3，他引：0  

Chang-Jo Chung  Andrea G. Fabbri   《Geomorphology》2008,94(3-4):438

A landslide-hazard map is intended to show the location of future slope instability. Most spatial models of the hazard lack reliability tests of the procedures and predictions for estimating the probabilities of future landslides, thus precluding use of the maps for probabilistic risk analysis. To correct this deficiency we propose a systematic procedure comprising two analytical steps: “relative-hazard mapping” and “empirical probability estimation”. A mathematical model first generates a prediction map by dividing an area into “prediction” classes according to the relative likelihood of occurrence of future landslides, conditional by local geomorphic and topographic characteristics. The second stage estimates empirically the probability of landslide occurrence in each prediction class, by applying a cross-validation technique. Cross-validation, a “blind test” here using non-overlapping spatial or temporal subsets of mapped landslides, evaluates accuracy of the prediction and from the resulting statistics estimates occurrence probabilities of future landslides. This quantitative approach, exemplified by several experiments in an area near Lisbon, Portugal, can accommodate any subsequent analysis of landslide risk.  相似文献