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211.
汶川-映秀8.0级大地震发生在由3条NE向断裂带组成的龙门山逆冲走滑断裂系上,造成了以汶川、映秀为中心和其周边地域的严重破坏和人员的重大伤亡.然而强烈地震发生前却未见有可能的确切征兆或浅表层异常活动的迹象(相对于短期和临震预测),即浅层过程与地震发生的深层过程并不匹配.那么为什么在龙门山地区突然发生了这次大地震,它具有哪些特征?其成因机制又是什么?为此必须对这次强烈地震"孕育"、发生和发展的壳、幔速度结构以及其深层动力过程进行深入研究和探讨.通过对松藩-甘孜、龙门山造山带和四川盆地地域人工源地震深部探测以及天然地震层析成像、接收函数与面波频散反演研究分析,初步结果表明:1)在印度洋板块与欧亚板块陆-陆碰撞和挤压作用下,形成了喜马拉雅造山带和东构造结,该东构造结似一尖楔向NNE方向顶挤并插入青藏高原东北缘,故迫使高原深部物质向东流展.在受到以龙门山为西北边界的四川盆地高速"刚性"物质阻隔下,一部分物质则转而向东南侧向运移;2)龙门山造山带与其西北侧地带地形高差达3500±500m左右,地壳厚度在龙门山西北部为65±5km左右,四川盆地为40±2km左右,而龙门山地带与其东、西两侧相比则其地壳厚度变化幅度达15~20km,这里恰为应力作用的耦合与集中地带;3)下地壳和地幔盖层物质以上、中地壳(深20~25km)中的低速层为第一滑移面,以上地幔软流层顶面为第二滑移面,且在四川盆地深部"刚性"物质阻隔下,下地壳和上地幔盖层物质以高角度在龙门山断裂系与四川盆地的耦合地带向上运移(或称逆冲),且在龙门山地表3条断裂构成的断裂系向下收敛到15±5km左右深处汇聚,二者强烈碰撞、挤压和震源介质破裂;即存物质与能量的强烈交换下,高度集中的应力得到急速释放,故形成了这次8.0级大地震.为此通过该区的壳、幔速度结构变异,初步揭示了这次8.0级大地震"孕育"、发生和发展的深部介质和构造环境及其深层动力过程. 相似文献
212.
By using the numerical method to model the ter-rain effect on the magnetotelluric field,few resultshave been obtained. The finite element method(FEM) was used by Chouteau and Bouchard (1988)and Wannamaker et al .(1986) ,andthe boundary el-ement method (BEM) was used by Xu and Zhou(1997) and Xu (1995) to model 2Dtopographyinflu-ences on magnetotelluric surveys . The BEM methodwas also used to model the 3Dtopographic effect onmagnetotelluric deep sounding (Xu et al .,1997 ;Xu,1995) .In t… 相似文献
213.
Surface geochemical exploration for oil and gas is still in the empirical stage,despite50 years has passed since the method was first proposed by Laubmeyer and Sokolov.Aboom of its application is emerging in China followed the depression during60 -70‘s.However,before the method can be accepted by the industry as a routine technique,a rel-atively sound basis should be established.This paper presents several cases overknown oil and gas fields and discusses the factors that effect the surface geochemical ex-pression of underground oil pools. 相似文献
214.
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216.
震灾保险新制式是地震科技导入保险营运过程以强化其科学性,规范性的一次创新尝试;制式的推行同时将给保险与系统的联手协作主各自相关业务的拓展带来新的概念和新的该文论述了这种合作的方式和特点,并向人们展示了合作必将获妈巨大社会效益的良好前景。 相似文献
217.
笔者分析了39例MRI脑内海绵状血管瘤病人的图像资料,并对CT、MRI、DSA的诊断价值进行了比较,MRI多次出血信号特征和CT钙化灶是其特点,笔者认为CT、MRI综合分析,是对本病进行无损伤性检查的首选方法。 相似文献
218.
花岗岩不同土地利用类型坡地水土流失特征* 总被引:17,自引:0,他引:17
利用福建省安溪水土保持试验站的实测资料,对花岗岩不同土地利用类型坡地的水土流失特征进行了初步研究,试验结果说明,坡地只要有一定的植被覆盖和适当的坡地工程,水土流失均可得到控制.松耕使坡耕地土壤侵蚀力急剧下降,必须加强夏季园面覆盖.建议利用USLE进行土壤侵蚀预测时,未扰动自然课露坡地C取值0.1-0.3.实测结果显示,香根草带和牧草覆盖均有良好的保持水土效益,与山边沟工程结合,可以在较陡坡地果园开发中替代梯田台地进行推广. 相似文献
219.
Molecular Records of Primary Producers and Sedimentary Environmental Conditions of Late Permian Rocks in Northeast Sichuan, China 总被引:2,自引:0,他引:2
A series of biomarkers were identified in the aliphatic and aromatic fractions of the extracts from Late Permian Dalong (大隆) and Wujiaping (吴家坪) formations in Shangsi (上寺) Section, Northeast Sichuan (四川), South China, on the basis of the analysis of gas chromatography-mass spectrometry (GC-MC). The dominance of lower-molecular-weight n-alkanes throughout the profile suggests the dominant contribution of algae and bacteria to the organics preserved in the marine section. Wujiaping Formation is characterized by the elevated contribution from algae as well as other photoantotrophs such as photosynthetic bacteria as shown by the molecular ratios of hopanes to steranes or tricyclic terpanes as well as the ratio of pristane (Pr) and phytane (Ph) to C17 and C18 n-alkanes. This is in accord with the data from the microscopic measurement on the calcareous algae. In contrast, Dalong Formation is featured by enhanced contribution from bacteria and probably terrestrial organics indicated by the enhanced C24 tetracyclic terpanes relative to tricyclic terpanes. The two formations also show a distinct discrimination in sedimentary environmental conditions including redox condition and salinity. The anoxic condition was only found in the middle of the Dalong Formation as shown by the ratios of Pr/Ph and dibenzothiophene to phenanthrene, consistent with the reported data of Mo and U. An enhancedsalinity indicated by the homohopane index is observed at the shallow Wujiaping Formation. On the basis of the composition of primary productivity and the redox condition, Dalong Formation is proposed, herein, to be potential hydrocarbon source rocks in the study site. It is notable that the topmost end-Permian is characterized by a large perturbance in both the redox condition and salinity, with oxic conditions being frequently interrupted by short-term anoxia, likely showing a causal relationship with the episodic biotic crisis across the Permian-Triassic boundary. 相似文献
220.
Because oxygen deficient conditions enhance the preservation of depositional organic matter, analysis on paleooxygenation conditions of depositional environments becomes a routine work in evaluations of potential hydrocarbon source rocks. The article focuses on depositional and ecological features relating to oxygen deficient shelfal environments at the Shangsi (上寺) Section, as a part of multidiscipline collaboration to reevaluate the hydrocarbon potential of the Middle and Upper Permian, Guangyuan (广元), Northeast Sichuan (四川) Province. Icbnofabric Zoophycos, sepioilte-bearing limestones (SBL) were interpreted as indicators of dysaerobic environments. Laminated calcareous and/or siliceous mudstones with pelagic ammonites and radiolarians were believed to be the deposits of anaerobic environments. When rhythmic succession was considered, average strategy was adopted for the oxygenation explanation of a given intervaL The anaerobic condition in this Permian section was observed in the upper part of the latest Permian Dalong (大隆) Formation, in which siliceous mudstones with ammonite, radiolarians develop in association with lower U/Mo ratio, lower biomarker ratio of Pr/Ph, and the highest TOC content. The topmost Maokou (茅口) Formation, featured by thin-bedded calcareous and siliceous mudstones with ammonite, thin-shelled bivalves, and laminations would be deposits of the quasianaerobic condition. The middle part of the Members and Ⅲ of the Chihsia Formation is proposed to be dysaerobic condition as indicated by occurrences of SBL and ichnofabric features, with the Member Ⅲ being the severe dysaerobic condition. 相似文献