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   

Steel buckling‐restrained braced frames with single and dual corner gusset connections: seismic tests and analyses     

Chung‐Che Chou  Jia‐Hau Liu  Dinh‐Hai Pham 《地震工程与结构动力学》2012,41(7):1137-1156

The design of a three‐story buckling‐restrained braced frame (BRBF) with a single‐diagonal sandwiched BRB and corner gusset was evaluated in cyclic tests of a one‐story, one‐bay BRBF subassembly and dynamic analyses of the frame subjected to earthquakes. The test focused on evaluating (1) the seismic performance of a sandwiched BRB installed in a frame, (2) the effects of free‐edge stiffeners and dual gusset configurations on the corner gusset behavior, (3) the frame and brace action forces in the corner gusset, and (4) the failure mode of the BRBF under the maximum considerable earthquake level. The subassembly frame performed well up to a drift of 2.5% with a maximum axial strain of 1.7% in the BRB. Without free‐edge stiffeners, the single corner gusset plate buckled at a significantly lower strength than that predicted by the specificationof American Institute of Steel Construction (2005). The buckling could be eliminated by using dual corner gusset plates similar in size to the single gusset plate. At low drifts, the frame action force on the corner gusset was of the same magnitude as the brace force. At high drifts, however, the frame action force significantly increased and caused weld fractures at column‐to‐gusset edges. Nonlinear time history analyses were performed on the three‐story BRBF to obtain seismic demands under both design and maximum considerable levels of earthquake loading. The analytical results confirmed that the BRB and corner gusset plate achieved peak drift under cyclic loading test. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Seismic performance evaluation of a 34‐story steel building retrofitted with response modification elements     

Yuan‐Tao Weng  Keh‐Chyuan Tsai  Pei‐Ching Chen  Chung‐Che Chou  Ya‐Ran Chan  Sheng‐Jhih Jhuang  Yung‐Yu Wang 《地震工程与结构动力学》2009,38(6):759-781

The original structural design of this case study consisted of five basement floors and a 34‐story hotel tower in Kaohsiung, Taiwan. The construction started in 1993, and the erection of the entire steel frame and the pouring of concrete slabs up to the 26th floor were completed before 1996. However, construction of the original hotel was subsequently suspended for 10 years. Recently, this building has been retrofitted for residential purposes. Buckling restrained braces (BRBs) and eccentrically braced frames were incorporated into the seismic design of the new residential tower. This paper presents the seismic resisting structural system, seismic design criteria, full‐scale test results of one BRB member and the as‐built welded moment connections. Test results confirm that the two side web‐plate stiffening details can effectively improve the rotational capacity of welded moment connection. The paper also discusses the analytical models for simulating the experimental responses of the BRB members and the welded moment connections. Nonlinear response history analyses (NLRHA) indicate that the inelastic deformational demands of the original and the redesigned structures induced by the maximum considered earthquakes are less than those found in the seismic building codes or laboratory tests. This paper also proposes a ground motion scaling method considering multi‐mode effects for NLRHA of the example building. It is shown that the proposed scaling method worked well in reducing the scatter in estimated peak seismic demands. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

Geochronology and petrogenesis of granitic rocks in Gangdese batholith,southern Tibet   总被引：18，自引：0，他引：18  

WeiQiang Ji  FuYuan Wu  ChuanZhou Liu  SunLin Chung 《中国科学D辑(英文版)》2009,52(9):1240-1261

Based on petrological and geochemical characteristics such as rock assemblage, petrogeochemistry, Sr-Nd isotope, zircon U-Pb age, and Hf isotope, we studied geochronological framework, magma types, source characters, and petrogenesis of different stages of magmatism of the granitic rocks from the Gangdese batholith in southern Tibet. The magmatic activities of the Gangdese batholith can be divided into three stages. The Mesozoic magmatism, induced by northern subduction of Neotethyan slab, was continuously ...  相似文献   

Optimal design theories of tuned mass dampers with nonlinear viscous damping     

Lap-Loi Chung  Hsu-Hui Huang  Chung-Hsin Chang  Kuan-Hua Lien 《地震工程与工程振动(英文版)》2009,8(4):547-560

Optimal design theory for linear tuned mass dampers(TMD) has been thoroughly investigated,but is still under development for nonlinear TMDs.In this paper,optimization procedures in the time domain are proposed for design of a TMD with nonlinear viscous damping.A dynamic analysis of a structure implemented with a nonlinear TMD is conducted fi rst.Optimum design parameters for the nonlinear TMD are searched using an optimization method to minimize the performance index.The feasibility of the proposed optimiza...  相似文献