Earthquake source time-function from coherent and incoherent rupture     

Junji Koyama 《Tectonophysics》1985,118(3-4)

Theoretical study has been made investigating the seismic source spectrum generated from a coherent and incoherent rupture. An earthquake is modeled by a finite propagating rupture on a fault plane where fault heterogeneities, fault patches, are randomly distributed. The dislocation velocity of such a fracture is assumed to be approximated by a stochastic process of random impacts of particles obeying Brownian motion. The parameters of the present stochastic source are seismic moment, fault dimension, fault patch intensity, and patch fracture time. The model predicts two corner frequencies; one originates from the fault finiteness and the other from the fracturing of fault patches. The seismic source spectrum from the model consequently shows distinct frequency dependence of ω⁰ − ω⁻² − ω^−γ − ω⁻² with increasing angular frequency ω, where γ is about 1.0. The seismic moment is controlled by an average dislocation on the fault and by the fault dimension. The short-period spectrum, which is much more abundant than that of the ordinary deterministic models, is controlled by the product of the fault patch intensity and the square root of their total number. The ω⁻² high frequency asymptote of the theoretical spectrum is in conformity with the white acceleration spectrum usually found in the literature, and it guarantees the finite total energy of the rupture process.  相似文献   

Late Neogene loess deposition in southern Tarim Basin: tectonic and palaeoenvironmental implications   总被引：2，自引：0，他引：2  

Hongbo Zheng  Chris McA Powell  Katherine Butcher  Junji Cao 《Tectonophysics》2003,375(1-4):49

Uplift of the Tibetan Plateau during the late Cainozoic resulted in a thick apron of molassic sediments along the northern piedmonts of the Kunlun and Altyn Mountains in the southern Tarim Basin. Early Neogene sediments are characterised by sandstone, siltstone and red mudstone, representing floodplain to distal alluvial fan environments. The Early Pliocene Artux Formation consists of medium-grained sandstone and sandy mudstone with thin layers of fine pebbly gritstone. The Late Pliocene to Early Pleistocene Xiyu Formation is dominated by pebble to boulder conglomerate typical of alluvial fan debris flow deposits. Sedimentological investigation, together with grain size and chemical analyses of siltstone bands intercalated with sandstone and conglomerate in the Xiyu and Artux Formations, point to an aeolian origin, suggesting desertic conditions in the Tarim Basin by the Early Pliocene. The onset of aeolian sedimentation in the southern Tarim Basin coincided with uplift of the northern Tibetan Plateau inferred from the lithofacies change from fine-grained mudstone and sandstone to coarse clasts. Tibetan Plateau uplift resulted in the shift of sedimentary environments northwards into the southern Tarim Basin, and could well have triggered the onset of full aridity in the Taklimakan region as a whole.  相似文献   

Cenozoic Volcanism in South China Sea and Its Vicinity and South China Sea Spreading   总被引：1，自引：0，他引：1  

Zhao Hailing  Deng Jinfu  Li Kaiming  Di Yongjun  Yu Junji  Zhao Jianhua  Li Yonghua 《中国地质大学学报(英文版)》2002,13(3)

The rock series, rock types and Sr-Nd isotopic dating of the Cenozoic volcanic rocks in the South China Sea are similar to those in its vicinity. On the basis of the spreading age of the South China Sea, the Cenozoic volcanic rocks are divided into three stages: the pre-spreading stage, the spreading stage and the post-spreading stage. The deep process characteristics of the asthenosphere and lithosphere may be inferred from the study on primary basaltic magma. The top layers of the asthenosphere both in the spreading stage and in the pre-spreading stage are closer to the earth surface than that in the post-spreading stage. From the pre-spreading stage to the spreading stage, the top layer of the asthenosphere decreased in depth, while the amount of interstitial partial melts increased. The evolution of the primary basaltic magma shows a progressive evolution sequence of the rifting volcanism and a faster lithospheric spreading velocity. From the spreading stage to the post-spreading stage, the top layer of the asthenosphere gradually increased in depth, but the amount of interstitial partial melts decreased. The evolution of primary basaltic magma shows a retrogressive evolution sequence of the rifting volcanism and a gradual decrease in the lithospheric spreading velocity. The depth recognized by the study on the Cenozoic volcanism demonstrates the deep environment for the formation and evolution of the South China Sea.  相似文献   

Methods for determining minimum freshwater inflow needs of Texas bays and estuaries     

Gary L. Powell  Junji Matsumoto  David A. Brock 《Estuaries and Coasts》2002,25(6):1262-1274

In response to legislative directives beginning in 1975, the Texas Water Development Board (TWDB) and the Texas Parks and Wildlife Department (TPWD) jointly established and currently maintain a data collection and analytical study program focused on determining the effects of and needs for freshwater inflows into the state's 10 bay and estuary systems. Study elements include hydrographic surveys, hydrodynamic modeling of circulation and salinity patterns, sediment analyses, nutrient analyses, fisheries analyses, freshwater inflow optimization modeling, and verification of needs. For determining the needs, statistical regression models are developed among freshwater inflows, salinities, and coastal fisheries. Results from the models and analyses are placed into the Texas Estuarine Mathematical Programming (TxEMP) model, along with information on salinity viability limits, nutrient budgets, fishery biomass ratios, and inflow bounds. The numerical relationships are solved within the constraints and limits, and optimized to meet state management objectives for maintenance of biological productivity and overall ecological health. Solution curves from the TxEMP model are verified by TWDB’s hydrodynamic simulation of estuarine circulation and salinity structure, which is evaluated against TPWD’s analysis of species abundance and distribution patterns in each bay and estuary system. An adequate system-wide match initially verifies the inflow solution. Long-term monitoring is recommended in order to verify that implementation of future water management strategies maintain ecological health of the estuaries and to provide an early warning of needs for adaptive management strategies.  相似文献   

Profiles and Source Apportionment of Nonmethane Volatile Organic Compounds in Winter and Summer in Xi’an,China, based on the Hybrid Environmental Receptor Model     

Jian SUN  Zhenxing SHEN  Yue ZHANG  Wenting DAI  Kun HE  Hongmei XU  Zhou ZHANG  Long CUI  Xuxiang LI  Yu HUANG  Junji CAO 《大气科学进展》2021,38(1):116-131

Summer and winter campaigns for the chemical compositions and sources of nonmethane hydrocarbons(NMHCs)and oxygenated volatile organic compounds(OVOCs)were conducted in Xi’an.Data from 57 photochemical assessment monitoring stations for NMHCs and 20 OVOC species were analyzed.Significant seasonal differences were noted for total VOC(TVOC,NMHCs and OVOCs)concentrations and compositions.The campaign-average TVOC concentrations in winter(85.3±60.6 ppbv)were almost twice those in summer(47.2±31.6 ppbv).Alkanes and OVOCs were the most abundant category in winter and summer,respectively.NMHCs,but not OVOCs,had significantly higher levels on weekends than on weekdays.Total ozone formation potential was higher in summer than in winter(by 50%)because of the high concentrations of alkenes(particularly isoprene),high temperature,and high solar radiation levels in summer.The Hybrid Environmental Receptor Model(HERM)was used to conduct source apportionment for atmospheric TVOCs in winter and summer,with excellent accuracy.HERM demonstrated its suitability in a situation where only partial source profile data were available.The HERM results indicated significantly different seasonal source contributions to TVOCs in Xi’an.In particular,coal and biomass burning had contributions greater than half in winter(53.4%),whereas traffic sources were prevalent in summer(53.1%).This study’s results highlight the need for targeted and adjustable VOC control measures that account for seasonal differences in Xi’an;such measures should target not only the severe problem with VOC pollution but also the problem of consequent secondary pollution(e.g.,from ozone and secondary organic aerosols).  相似文献   

Wind and buoyancy driven intermediate-layer overturning in the Sea of Okhotsk     

Junji Matsuda  Humio Mitsudera  Tomohiro Nakamura  Keisuke Uchimoto  Takuya Nakanowatari  Naoto Ebuchi 《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(9):1401-1418

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China's EarthLab——Forefront of Earth System Simulation Research     

Zhaoyang CHAI  He ZHANG  Mulan ZHANG  Xiao TANG  Weipeng ZHENG  Jiang ZHU  Guangqing ZHOU  Junji CAO  Qingcun ZENG 《大气科学进展》2021,38(10):1611-1620

This article introduces "EarthLab ", a major new Earth system numerical simulation facility developed in China.EarthLab is a numerical simulation system for a physical climate system, an environmental system, an ecological system, a solid earth system, and a space weather system as a whole with a high-performance scientific computing platform.EarthLab consists of five key elements—namely: a global earth numerical simulation system, a regional high-precision simulation system, a supercomputing support and management system, a database, data assimilation and visualization system, and a high-performance computing system for earth sciences. EarthLab helps to study the atmosphere, hydrosphere,cryosphere, lithosphere, and biosphere, as well as their interactions, to improve the accuracy of predictions by integrating simulations and observations, and to provide a scientific foundation for major issues such as national disaster prevention and mitigation. The construction and operation of EarthLab will involve close cooperation with joint contributions and shared benefits.  相似文献   

湖光岩玛珥湖沉积记录的近250年重金属元素污染历史   总被引：1，自引：0，他引：1  

鲁海燕  曹军骥  韩永明  吴枫 《海洋地质与第四纪地质》2010,(1)

以湖光岩玛珥湖为研究对象,在放射性核素137Cs和210Pb精确定年的基础上,分析了沉积岩心柱中重金属元素V、Ni、Cu、Zn、Pb的垂直变化特征,探讨了近250年来湖泊沉积物重金属的污染历史,并利用富集系数法和地质累积指数法评价了重金属的污染程度。结果表明:1880年前,各元素含量基本保持稳定;1880—1920年,Ni、Cu、Zn、Pb含量增加可能与这一时期工业发展及战争有关;20世纪20年代Pb含量突然增加反映了全球含铅汽油的使用;Zn元素含量在1950年增加及20世纪70年代后期的明显增大,分别与新中国建立后工业的发展及中国改革开放后工业活动的显著增加相一致;1975—1990年,Pb含量的增加很可能与1978年改革后开放工业和交通发展有关;表层V、Zn、Pb元素含量的减少可能与80年代后环保事业的发展有关。V、Ni、Cu、Zn受人类活动影响较小,基本上属于无污染或轻微污染状态,Pb在20世纪20年代前为无污染或轻微污染,20年代后为中等程度的污染。  相似文献   

Evolution of carbon dioxide-bearing saline fluids in the mantle wedge beneath the Northeast Japan arc     

Yoshitaka?KumagaiEmail author  Tatsuhiko?Kawamoto  Junji?Yamamoto 《Contributions to Mineralogy and Petrology》2014,168(4):1056

Lherzolite xenoliths containing fluid inclusions from the Ichinomegata volcano, located on the rear-arc side of the Northeast Japan arc, may be considered as samples of the uppermost mantle above the melting region in the mantle wedge. Thus, these fluid inclusions provide valuable information on the nature of fluids present in the sub-arc mantle. The inclusions in the Ichinomegata amphibole-bearing spinel–plagioclase lherzolite xenoliths were found to be composed mainly of CO₂–H₂O–Cl–S fluids. At equilibrium temperature of 920 °C, the fluid inclusions preserve pressures of 0.66–0.78 GPa, which correspond to depths of 23–28 km. The molar fraction of H₂O and the salinity of fluid inclusions are 0.18–0.35 and 3.71 ± 0.78 wt% NaCl equivalent, respectively. These fluid inclusions are not believed to be fluids derived directly from the subducting slab, but rather fluids exsolved from sub-arc basaltic magmas that are formed through partial melting of mantle wedge triggered by slab-derived fluids.  相似文献   

Chemical composition of rainwater at Lijiang on the Southeast Tibetan Plateau: influences from various air mass sources     

Ningning Zhang  Junji Cao  Yuanqing He  Shun Xiao 《Journal of Atmospheric Chemistry》2014,71(2):157-174

Daily rainwater samples collected at Lijiang in 2009 were analyzed for pH, electrical conductivity, major ion (SO₄ ^2?, Cl^?, NO₃ ^?, Na⁺, Ca²⁺, Mg²⁺, and NH₄ ⁺) concentrations, and δ¹⁸O. The rainwater was alkaline with the volume-weighted mean pH of 6.34 (range: 5.71 to 7.11). Ion concentrations and δ¹⁸O during the pre-monsoon period were higher than in the monsoon. Air mass trajectories indicated that water vapor from South Asia was polluted with biomass burning emissions during the pre-monsoon. Precipitation during the monsoon was mainly transported by flow from the Bay of Bengal, and it showed high sea salt ion concentrations. Some precipitation brought by southwest monsoon originated from Burma; it was characterized by low δ¹⁸O and low sea salt, indicating that the water vapor from the region was mainly recycled monsoon precipitation. Water vapor from South China contained large quantities of SO₄ ^2?, NO₃ ^?, and NH₄ ⁺. Throughout the study, Ca²⁺ was the main neutralizing agent. Positive matrix factorization analysis indicated that crustal dust sources contributed the following percentages of the ions Ca²⁺ 85 %, Mg²⁺ 75 %, K⁺ 61 %, NO₃ ^? 32 % and SO₄ ^2? 21 %. Anthropogenic sources accounted for 79 %, 68 %, and 76 % of the SO₄ ^2?, NO₃ ^? and NH₄ ⁺, respectively; and approximately 93 %, 99 %, and 37 % of the Cl^?, Na⁺, and K⁺ were from a sea salt source.  相似文献