Lg Coda Q and its Relation to the Geology and Tectonics of the Middle East     

L. Cong  B. J. Mitchell 《Pure and Applied Geophysics》1998,153(2-4):563-585

—Regional seismograms were collected to image the lateral variations of Lg coda Q at 1 Hz (Q ₀?) and its frequency dependence <(eta)> in the Middle East using a back-projection method. The data include 124 vertical-component traces recorded at 10 stations during the period 1986–1996. The resulting images reveal lateral variations in both Q ₀ and <eta>. In the Turkish and Iranian Plateaus, a highly deformed and tectonically active region, Q ₀ ranges between about 150 and 300, with the lowest values occurring in western Anatolia where extremely high heat flow has been measured. The low Q ₀ values found in this region agree with those found in other tectonically active regions of the world. Throughout most of the Arabian Peninsula, a relatively stable region, Q ₀ varies between 350 and 450, being highest in the shield area and lowest in the eastern basins. All values are considerably lower than those found in most other stable regions. Low Q values throughout the Middle East may be caused by interstitial fluids that have migrated to the crust from the upper mantle, where they were probably generated by hydrothermal reactions at elevated temperatures known to occur there. Low Q ₀ values (about 250) are also found in the Oman folded zone, a region with thick sedimentary deposits. <eta> varies inversely with Q ₀ throughout most of the Middle East, with lower values (0.4–0.5) in the Arabian Peninsula and higher values (0.6–0.8) in Iran and Turkey. Q ₀ and <eta> are both low in the Oman folded zone and western Anatolia.  相似文献   

Seismic Velocity and Q Structure of the Middle Eastern Crust and Upper Mantle from Surface-wave Dispersion and Attenuation     

L. Cong  B. J. Mitchell 《Pure and Applied Geophysics》1998,153(2-4):503-538

—Observed velocities and attenuation of fundamental-mode Rayleigh waves in the period range 7–82 sec were inverted for shear-wave velocity and shear-wave Q structure in the Middle East using a two-station method. Additional information on Q structure variation within each region was obtained by studying amplitude spectra of fundamental-mode and higher-mode Rayleigh waves. We obtained models for the Turkish and Iranian Plateaus (Region 1), areas surrounding and including the Black and Caspian Seas (Region 2), and the Arabian Peninsula (Region 3). The effect of continent-ocean boundaries and mixed paths in Region 2 may lead to unrealistic features in the models obtained there. At lower crustal and upper-mantle depths, shear velocities are similar in all three regions. Shear velocities vary significantly in the uppermost 10 km of the crust, being 3.21, 2.85, and 3.39 km/s for Regions 1, 2, and 3, respectively. Q models obtained from an inversion of interstation attenuation data show that crustal shear-wave Q is highest in Region 3 and lowest in Region 1. Q’s for the upper 10 km of the crust are 63, 71, and 201 for Regions 1, 2, and 3, respectively. Crustal Q’s at 30 km depth for the three regions are about 51, 71, and 134. The lower crustal Q values contrast sharply with results from stable continental regions where shear-wave Q may reach one thousand or more. These low values may indicate that fluids reside in faults, cracks, and permeable rock at lower crustal, as well as upper crustal depths due to convergence and intense deformation at all depths in the Middle Eastern crust.  相似文献   

Lg Coda Q and its Relation to the Structure and Evolution of Continents: A Global Perspective     

B. J. Mitchell  Lianli Cong 《Pure and Applied Geophysics》1998,153(2-4):655-663

—Tomographic maps of Lg coda Q (Q ^c _Lg) variation are now available for nearly the entire African, Eurasian, South American, and Australian continents, as well as for the United States. Q ^c _Lg at 1 Hz (Q ₀) varies from less than 200 to more than 1000 and Q ^c _Lg frequency dependence (<eta>) varies between 0.0 and nearly 1.0. Q ₀ appears to increase in proportion to the length of time that has elapsed since the most recent major episode of tectonic or orogenic activity in any region. A plot of Q ₀ versus time since that activity indicates that a single Q ₀-time relation approximates most mean Q ₀ values. Those that deviate most from the trend lay in Australia, the Arabian Peninsula, and the East African rift. The increase in Q ₀ with time may be due to a continual increase in crustal shear wave Q (Q ) caused by the loss of crustal fluids and reduction of crustal permeability following tectonic or orogenic activity. Extrapolated values of Q ^c _Lg at 5 Hz (using Q ₀ and <eta> values measured at 1 Hz and assuming that <eta> is constant in all regions between 1 and 5 Hz) show a similar percentage-wise increase with times that has elapsed since the most recent activity. Other factors that can reduce Q ₀ in continental regions include thick accumulations of sediment (especially sandstone and shale of Mesozoic age and younger), severe velocity gradients at the crust-mantle transition and, possibly, lateral variations in the depth, thickness, and severity of those gradients. Severe and large increases of Q in the mid-crust of some regions can cause relatively large values of <eta>, even if the frequency dependence of Q is small.  相似文献   

11-deoxyheloside A的合成     

张雪微  王鹏  宋妮  张秀丽  王聪  李明 《中国海洋大学学报(自然科学版)》2015,(4):72-77

首次完成天然胆甾烷型皂苷11-deoxyheloside A的合成。在相转移催化的条件下,葡萄糖溴苷1与膦酸单乙酯2反应以69%的收率得到葡萄糖膦酸酯供体3;以胆甾烷苷元4为原料,经Luche还原和乙酰化反应以及三氟甲磺酸负载硅胶脱除TBDPS基团得到胆甾烷二醇10;在金催化剂的作用下,胆甾二醇10与葡萄糖膦酸酯供体3进行糖苷化反应,然后脱除酰基保护基以97%的产率完成11-deoxyheloside A的合成。  相似文献   

鄂尔多斯盆地西峰地区延长组烃源岩两环烷烃分布特征及其生源     

吉利明  梁晓飞  贺聪  吴远东 《地球科学与环境学报》2015,(1):76-84

鄂尔多斯盆地西南部西峰地区三叠系延长组烃源岩检出丰富的两环烷烃,主要为C12~C14和C15、C16两组两环烷烃。其相对丰度表现出3种源岩模式:1以低碳数两环烷烃为主,出现于长71和长81段非烃源岩;2两组两环烷烃都很丰富,出现于长73段富有机质烃源岩;3以高碳数两环烷烃为主,主要发现于长73段烃源岩,也见于长72和长81段。尽管长7段热演化程度基本一致,但补身烷异构化指数变化明显,表明补身烷重排不仅受热演化的影响,而且受有机质来源和沉积环境的控制。延长组烃源岩具有明显的高补身烷优势,反映了烃源岩的还原性沉积环境。烃源岩高丰度C15、C16两环烷烃的检出则指示该地区晚三叠世发育淡水湖泊。葡萄藻不仅是该地区中生界石油的重要母质来源,而且可能是这些两环类标志物的直接生源。  相似文献   

虚拟仿真技术在测绘工程实践教学中的应用     

岳祥楠  贺小星  马飞虎  曾聪 《测绘工程》2021,30(1):76-80

实践教学是测绘工程本科教学中不可缺少的关键环节,文中结合当前测绘专业实践教学需求及其存在的不足,构建多种实验组合的虚拟仿真实践教学平台,实现网上演示教学、训练、实践指导和考核反馈等功能,形成"产-学-研"合一的实践教学体系.该平台便于学生课外自主学习,丰富实践教学的项目,实现精细化教学质量控制,发展学生的创新思维和综合应用能力,可供其他对仪器操作技能要求较高的类似课程或专业开展网络教学和构建实践教学平台借鉴.  相似文献   

一种风暴轴逐日监测的方法及应用   总被引：1，自引：1，他引：0  

顾聪  朱伟军 《气象科学》2015,35(3):268-278

提出了一种风暴轴逐日监测的方法, 可以获得逐日的风暴轴变化情况。并且采用了动态阈值定义了新的风暴轴的强度和位置指数, 从而可以有效对比不同层次、不同区域、不同时间的风暴轴变化情况。利用NCEP/NCAR再分析资料进行了监测结果的诊断分析。结果表明:各气象要素滤波结果都能表现出两个风暴轴主体, 但有位置上的差别。同时可以利用逐日检测的结果求得逐候、逐月的风暴轴监测结果。在不同高度的风暴轴中, 250~300 hPa高度的风暴轴强度最大, 850 hPa有极小值出现, 各层风暴轴强度呈现准正压结构。采用500 hPa高度场风暴轴监测结果做代表, 讨论了两大洋上各自的风暴轴偏强/偏弱、偏东/偏西、偏北/偏南时同期大气环流的500 hPa高度场和300 hPa纬向风场差异。  相似文献   

黄山不同高度雨滴谱的演变特征   总被引：1，自引：0，他引：1       下载免费PDF全文

陈聪  银燕  陈宝君 《大气科学学报》2015,38(3):388-395

选取2011年6月黄山地区一次降水过程,利用测得的雨滴谱资料对不同高度上降水微物理量及雨滴谱分布特征进行分析,并讨论其中的差异。结果表明:此次降水较强,各直径微物理量在山腰最大、山底次之、山顶最小;山腰的雨强最大,而山顶数浓度最大。在雨滴谱分布中,小于1mm的雨滴数密度是山顶大于山腰大于山底,这与小雨滴的蒸发和碰并有关;大于1.5 mm的雨滴数密度则是山腰大于山顶和山底,这可能与地形抬升使得云系加强有关。由各微物理量的时间序列可将降水过程分为两个阶段,第一阶段各微物理量值明显大于第二阶段,其中第一阶段的降水量约为第二阶段的3倍。雨强与雷达反射率、数浓度、最大直径近似成幂函数关系,其中雨强与雷达反射率相关性最好。  相似文献   

登陆广东热带气旋特征及其与副热带高压的关系   总被引：4，自引：1，他引：3  

曾琮  易爱民  李晓娟  梁巧倩  汪瑛  谢健标 《气象科技》2007,35(1):36-39

2004年登陆广东的热带气旋只有2个,个数明显偏少,粤西无热带气旋登陆;登陆广东的初台偏迟,终台结束早,登陆时间集中于7月;热带气旋移速快,强度弱(为热带风暴),对广东影响利大于弊。对1951~2004年7~9月登陆广东的热带气旋进行统计分析,发现各月登陆广东的热带气旋次数差异较大,最多时一个月有5个,最少时没有。登陆广东的热带气旋个数与西北太平洋副热带高压位置、强度有密切关系,可以将有利于和不利于热带气旋登陆广东的副热带高压各分为3种环流形势。  相似文献   

苏北超高压变质带榴辉岩的对比性研究及成矿作用     

黄建平  马东升  刘聪  王辉 《高校地质学报》2010,16(3)

苏北超高压变质带是秦岭—大别造山带的东延部分,所产出的榴辉岩有三种类型,分别为产于片麻岩中的G类榴辉岩、产于大理岩中的M类榴辉岩和产于蛇纹岩中P类榴辉岩。地球化学研究表明,三类榴辉岩的原岩复杂多样,源岩为下地壳或上地幔的基性-超基性岩,兼具大陆和大洋玄武岩的特征,富含TiO2等有用组分,是金红石矿床的成矿母岩。金红石矿床的形成是华北、扬子两大板块俯冲碰撞的结果,金红石成矿作用的强弱与岩性、构造、变质变形作用等密切相关。榴辉岩中含有金红石、钛铁矿、磷灰石、石榴子石、绿辉石等多种有用矿物,具有较高的综合利用价值。  相似文献