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   

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   

Late Quaternary sedimentation in the Kadeok region, Korea     

C. S. Lee  Y. H. Chung 《Geo-Marine Letters》2000,20(2):72-79

Analyses of high-resolution seismic-reflection data and geological samples revealed the characteristics of Quaternary sedimentation in the Kadeok region at the opening of the Nakdong River. The sediments comprise two layers, i.e., a 20- to 45-m-thick Holocene mud layer, and a coarser late-Pleistocene layer deposited in a fluvial environment. Sedimentological variations in the late-Pleistocene layer to the west and east of Kadeok Island are due to differences in channel maturity prior to the Holocene transgression. Holocene mud in the sea to the west of Kadeok Island was transported through a passway north of the island. Received: 26 October 1999 / Revision accepted: 7 February 2000  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   

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