地震分析中人工边界处理与地震动输入方法研究   总被引：8，自引：0，他引：8  

邱流潮  金峰 《岩土力学》2006,27(9):1501-1504

基于柱面波波动方程,推导建立了适用于土-结构地震动力相互作用分析的地震动输入和人工边界的处理方法.其中,地震动的输入是通过在人工边界上施加等效节点力来实现的,等效节点力的大小与入射地震波波速成正比;而人工边界的处理方法使得人工边界条件不仅在时间上是局部的,而且在空间上也是局部的.这种处理方法简单、有效,物理意义清晰,且很容易在有限元法中实现,结合Newmark时间积分是无条件稳定的.为了验证方法的有效性和精度,给出了两个算例,分别用于检验人工边界条件的性能以及地震动输入方法的正确性.算例分析结果表明,所提出的方法是十分有效的.  相似文献   

珠江口盆地Site4B柱状沉积物中脂肪醇分子化合物分布及其来源分析     

茅晟懿  朱小畏  孙永革  管红香  吴能友 《海洋与湖沼》2014,45(6):1202-1217

本研究采用色谱质谱(GC-MS)和色谱-同位素质谱(GC-IRMS)方法,对珠江口盆地Site4B沉积物中脂肪醇分子化合物分布以及单体碳同位素组成进行了研究。结果表明:长链脂肪醇碳优势指数(CPIC26—34:9.41—24.56)、平均碳链长度(ACLC26—34:28.85—29.99)以及n C26—n C30脂肪醇平均碳同位素组成(?29.13‰±0.87‰、?32.98‰±1.28‰和?32.73‰±1.61‰)均揭示了n C26—n C34脂肪醇属于陆源高等植物来源,n C16—n C20和n C24脂肪醇较正的碳同位素组成反映了化合物的海洋细菌来源,而n C22脂肪醇偏负的碳同位素特征(平均?33.26‰±1.51‰)反映了化学自养细菌来源。Site4B沉积物中的陆源输入主要来自南海周边河流,从12.7ka BP至今的沉积时期(0—80cm,文中深度均为埋深)和末次冰盛期(102—120cm),其陆源输入主要来自台湾岛河流,而在19.3—12.7ka BP沉积时期(80—102cm)和更新世沉积时期(120—300cm),台湾岛、吕宋岛和珠江口河流的陆源贡献普遍较低。Site4B沉积物中的海洋生产力主要来自海洋微生物输入的贡献,并主要受到海水温差影响;其中在35—150cm层位,海洋输入和南海暖流的强弱带来的海水温度的高低有关,而在150—300cm层位,则主要和冰期-间冰期的冷暖气候带来的海水温差有关。  相似文献   

Origin of crude oils from oilfields in the Zagros Fold Belt,southern Iraq: Relation to organic matter input and paleoenvironmental conditions     

《Marine and Petroleum Geology》2016

Crude oil samples from Cretaceous and Tertiary reservoir sections in the Zagros Fold Belt oil fields, southern Iraq were investigated using non-biomarker and biomarker parameters. The results of this study have been used to assess source of organic matter, and the genetic link between oils and their potential source rocks in the basin. The oils are characterized by high sulphur and trace metal (Ni, V) contents and relatively low API gravity values (17.4–22.7° API). This indicates that these oils are heavy and generated from a marine source rock containing Type II-S kerogen. This is supported by their biomarker distributions of normal alkanes, regular isoprenoids, terpanes and steranes and the bulk carbon isotope compositions of their saturated and aromatic hydrocarbons. The oils are characterized by low Pr/Ph ratios (<1), high values of the C₃₅ homohopane index and C₃₁-22R/C₃₀ hopane ratios, relatively high C₂₇ sterane concentrations, and the predominance of C₂₉-norhopane. These biomarkers suggest that the oils were generated predominantly from a marine carbonate source rock, deposited under reducing conditions and containing plankton/algal and microorganisms source input. The presence of gammacerane also suggests water column stratification during source rock deposition.The biomarker characteristics of the oils are consistent with those of the Middle Jurassic Sargelu carbonate as the effective source rock in the basin. Biomarker maturity data indicate that the oils were generated from early maturity source rocks.  相似文献   

Spatial distribution of dust deposition within a small drainage basin: Implications for loess deposits in the Negev Desert   总被引：1，自引：0，他引：1  

Giora J. Kidron  Motti Zohar  Abraham Starinsky 《Sedimentology》2014,61(7):1908-1922

Loessial colluvial sediments and aeolian aprons are common deposits in the Negev Desert Highlands. In an attempt to monitor the amounts and distributional pattern of loess, monthly dust measurements were carried out during 2004 to 2006 in 10 cm diameter traps located at 18 stations along four slopes, north‐facing, south‐facing, east‐facing and west‐facing in a second‐order drainage basin near Sede Boqer, Negev Desert Highlands, Israel. Annual total dust depositions ranged between 110 g and 178 g m^?2 with an average of 151·1 g m^?2. The average annual dust deposition in the catchment was 23·5% higher than the average amount recorded at the hilltops (122·4 g m^?2) and may be a consequence of sheltering opportunities in the hilly topography. When analysed according to season and aspect, significantly higher monthly amounts were received during the wet rainy season of December to March (17·0 g m^?2), in comparison with the rest of the year (8·1 g m^?2). As for the aspect, while no significant differences characterized north‐facing and south‐facing slopes, east‐facing slopes received significantly higher amounts (by 43·3%) than west‐facing slopes, pointing to preferential dust deposition at the leeward slope. Concurring with the classical model that anticipates higher dust deposition at the leeside slope, but in disagreement with some reports published in the literature, the findings of this study were also supported by a field survey that showed preferential loess accumulation at the eastern and north‐eastern aspects. These findings may shed light on distributional patterns of colluvial sediments and aeolian aprons in the Negev, on soil‐forming processes and on past cycles of dust deposition.  相似文献   

多点输入条件下的土质边坡地震反应     

景鹏旭  杨清逸 《华北地震科学》2021,39(1):17-22

以二维土质边坡模型为例,地震输入方式分别采取单点输入和多点输入,考虑其土层地震反应、主应力极值等特征,分析单点、多点输入的差异;在此基础之上,探讨单点输入与多点输入下坡高、坡角的变化对土质边坡模型安全系数的影响。结果显示,在地震工程抗震设计时采用多点输入比单点输入更加安全、更符合实际情况。  相似文献   

Long-term dynamics of cultivated land resources and their driving forces of Guyuan City in upper reaches of Jinghe River     

CHEN Caocao XIE Gaodi ZHEN Lin LENG Yunfa 《中国地理科学(英文版)》2008,18(1):33-40

The land use patterns in Guyuan City, Ningxia Hui Autonomous Region of China, have changed greatly over the years, due to population growth and farming and stock raising development. This study, using 50-year statistical data of cultivated land and 14-year spatial data of land use pattern, analyzed the developmental stages, the character, and the spatial variance of farmland in the city, and discussed the driving forces of cultivated land changes based on empirical and conceptual statistical models. First, the change of cultivated land area went through different stages of rapid increase, fluctuating change, decrease and rapid decrease from 1949 to 2004, additionally, social and economic policies in different stages had an important impact on farmland variance. Second, from 1986 to 2000, the quantity of cultivated land increased, but its quality decreased. Third, social and economic factors are determinant factors in cultivated land transition. Five constructed paths explain cultivated land transition. Factors that have direct or indirect effects on farmland include the economy （Xeco）, the population （Xpop）, agricultural output （Xagr）, and scientific input （Xsci）. The sequence of impact was Xeco〉Xpop〉Xsci〉Xagr. Among all these impacts, Xeco was the major positive one, and Xpop was the major negative one. It is urgent to take measures or adopt a policy to stop the vicious cycle in eco-environment and agriculture production. Otherwise, negative patterns of farmland use will increase, and high-quality cultivated land will continue to decline.  相似文献   

冲绳海槽中部A7孔沉积物地球化学记录及其对古环境变化的响应   总被引：4，自引：0，他引：4  

李军 《海洋地质与第四纪地质》2007,27(1):37-45

对取自冲绳海槽中部的A7孔沉积物进行了元素地球化学的测试与分析,配合高分辨率测年和氧同位素数据,探讨了冲绳海槽中部18000年以来的元素地球化学变化特征及其控制因素。使用R型因子分析方法,将分析的20种常量与微量元素分为4个主要的因子:因子I主要由Al、Ti、Th、Rb、Mg、U和Zn等元素组成,代表了陆源物质有关的元素组合,可作为陆源物质输入的指示因子;因子II主要由Ca、Sr、Ba、P等元素组成,代表了与生物作用有关的元素组合,可作为古生物生产力指示因子。根据各元素及其组合随时间的变化特征,整个A7孔沉积物可明显分为4段:18-15 kaBP(Ⅰ),15-8 kaBP(Ⅱ),8-2 kaBP(Ⅲ)和2 kaBP以来(Ⅳ),前3段中都表现出陆源物质先增加再减少的变化趋势,古生物生产力的变化相对复杂,规律性不强,但总体表现出与陆源物质输入相反的变化趋势;第4段中则表现出2 kaBP年以来陆源物质的输入有一定的加强,而古生产力则没有大的变化。在7.3 kaBP左右发生的火山物质快速堆积事件对柱状沉积物的地球化学特征产生了较大的影响,也使陆源物质输入和古生物生产力急剧降低。自18 kaBP年以来,元素地球化学组成的变化主要受温度、海平面变化、黑潮水的“摆动”的影响,而火山沉积也造成了一定的影响。  相似文献