祁连山东南段加里东造山期构造变形年代的精确限定及其意义   总被引：8，自引：0，他引：8  

樊光明  雷东宁 《地球科学》2007,32(1):39-44

祁连山东南段呈北西-南东向展布着加里东期中祁连造山带和拉脊山造山带, 其基底为前加里东变质岩系, 在该变质结晶基底岩系中发育着菱形网格状韧性剪切带, 共轭韧性剪切带面对缩短方向的夹角为104°~114°, 其最大主应力方位为SW210°左右.在中祁连地块金沙峡和化隆地块科却两处韧性剪切带中的糜棱岩化岩石, 获取变质矿物白云母40Ar-39Ar坪年龄分别为(405.1±2.4) Ma和(418.3±2.8) Ma.这一年代学结果不仅确定了加里东基底变质岩系中韧性剪切带是加里东造山作用过程中形成, 更重要的是通过对基底韧性剪切带中变质变形岩石的年代学研究, 精确地限定了祁连山东南段的早古生代火山盆地(或岛弧盆地)、拉脊山小洋盆关闭的构造年代.这为造山带构造演化过程中盆地关闭时间的确定开辟了新的途径.   相似文献   

利用克里金技术标定新疆及附近地区P/S震相幅值比及其在地震事件识别中的应用   总被引：1，自引：1，他引：0       下载免费PDF全文

潘常周  靳平  肖卫国 《地震学报》2007,29(6):625-634

针对中国的乌鲁木齐台（WMQ）和哈萨克斯坦的马坎奇台（MAK）,采用贝叶斯克里金技术建立了新疆及附近地区地震事件的震相幅值比的校正曲面,并分析了校正曲面与地震波传播路径的关系,以及校正曲面对于改善震相幅值比判据识别效果的有效性.分析结果表明,建立的校正曲面基本合理,结合传播路径差异和地震波传播规律,能够较好地解释校正曲面的起伏特征. 而且,在传播路径差异较大,使得震相幅值比经震中距校正后离散度仍然较高的情况下,利用校正曲面修正震相幅值比,可以进一步降低其离散度,从而改善判据的识别效果.经校正曲面修正后,对天然地震的误识率由16.3%下降为5.2％.   相似文献   

太平洋SSTA同中国东部夏季极端降水事件变化关系的研究   总被引：3，自引：0，他引：3  

杨金虎  江志红  王鹏祥  杨启国 《海洋学报》2010,32(1):23-33

基于中国东部1955—2004年233个台站逐日降水和NCEP/NCAR再分析高度场、风场、比湿、地面气压以及NOAA海表温度资料,运用SVD、合成分析等方法研究了太平洋SSTA同中国东部夏季极端降水事件之间的相互关系,结果表明:前期冬季太平洋SSTA同我国东部夏季极端降水事件的关系比较显著;前冬赤道中东太平洋是影响我国华北地区夏季极端降水事件的关键区,若前冬该海域海温发生异常,从冬到夏大气环流先后通过PNA(反PNA)和WP(反WP)遥相关型使得西太平洋副热带高压发生异常,进而使得华北夏季极端降水事件发生异常;前冬热带西太平洋是影响我国东北南部及江南地区夏季极端降水事件的关键区,若前冬该海域海温发生异常,从冬到夏105°~135°E的平均经向垂直环流圈发生异常,使得夏季东北南部与江南地区垂直运动发生异常,进而使得东北南部和江南夏季极端降水事件发生异常。  相似文献   

极端事件再现时间长程相关性与群发性研究     

王启光  侯威  郑志海  冯爱霞  邓北胜 《海洋学报》2010,32(10):7491-7497

利用百分位阈值方法定义极端事件,从极端事件再现时间的角度,研究了极端事件发生时间间隔的长程相关性.发现若原时间序列具有长程相关性,则它的极端事件再现时间序列也具有长程相关性;计算表明两者的标度指数α相当接近,这一特性与随机产生的再现时间序列有着本质的差别,再现时间序列的长程相关性是由原序列的长程相关性决定的.具有长程相关性的时间序列再现时间的概率分布明显不同于随机序列,其小值再现时间的概率较大,反映出极端事件的群发现象.本文根据这一特征定义了再现时间的群发性指数,发现时间序列的长程相关性是导  相似文献   

The impact of extreme turbidity events on the nursery function of a temperate European estuary with regulated freshwater inflow     

E. González-Ortegón  M.D. Subida  J.A. Cuesta  A.M. Arias  C. Fernández-Delgado  P. Drake 《Estuarine, Coastal and Shelf Science》2010

Estuaries are used as nursery grounds by numerous marine species despite being usually subject to strong anthropogenic disturbances. Abundances of marine recruits (fish and crustacean decapods) and their main prey (mysids) were monitored by monthly sampling, from June 1997 to February 2009, in the lower reaches of the Guadalquivir estuary (SW Spain). During that period, unusually high and persistent turbidity events (HPTEs) were observed twice. Both HPTEs started with strong and sudden freshwater discharges after relatively long periods of very low freshwater inflow. Data from this time-series were used to test the hypothesis that HPTEs may negatively impact the nursery function of estuaries either by decreasing prey availability or by decreasing survival/arrival of marine recruits. During HPTEs, the commonest mysid (Mesopodopsis slabberi), a key species in the estuarine food web, showed a significant decrease in abundance. Likewise, some marine recruits that prey on M. slabberi and whose peaks of abundance within the estuary occur in summer–autumn (Engraulis encrasicolus and Pomadasys incisus) were less abundant during HPTEs. It is also suggested that HPTEs might have triggered a shift in the distribution of the most euryhaline prey (Neomysis integer) and predator (Dicentrarchus punctatus and Crangon crangon) species, towards more saline waters. This could have contributed to an increase in the inter-specific competition (for food/habitat) within the estuarine nursery area. The results discussed in this study call attention to the need to reduce as much as possible the anthropogenic pressures that may stimulate the occurrence of high and persistent turbidity events (HPTEs) in order to preserve the nursery function of temperate estuaries.  相似文献   

Mesoproterozoic Earthquake Events and Breakup of the Sino-Korean Plate   总被引：3，自引：0，他引：3  

QIAO Xiufu GAO Linzhi PENG Yang 《《地质学报》英文版》2007,81(3):385-397

In the Mesoproterozoic time, the northern part of the Sino-Korean Plate experienced a period of intensive tectonic extension and breakup. 1. An abundance of sedimentary earthquake records is preserved in the Chuanlinggou, Tuanshanzi and Gaoyuzhuang formations in the Mesoproterozoic Changcheng System （1800-1400 Ma） and in the Mesoproterozoic Wumishan Formation of the Jixian System （1400-1000 Ma）. These earthquake records are characterized by various liquefied sand-veins, carbonate microspar and coarser spar veins, limestone dikes, liquefied breccia and various forms of liquefied contorted bedding. This deformation is always associated with synsedimentary faults and igneous activity. 2. Three liquefaction models for soft carbonate sediments are recognized, including liquefaction in laminated carbonate rocks, liquefaction in thin-bedded carbonates and large-scale liquefaction along huge carbonate dikes. 3. Based on the record of earthquake and volcanic activities, the Sino-Korean Plate experienced at least twice intraplate breakups. One occurred between 1800-1400 Ma, and the other occurred at about 1200 Ma. The last breakup resulted in formation of the Yan-Liao aulacogen, a tectonic zone characterized by deeper material vibrancy, active faults, major igneous activity and frequent earthquakes.  相似文献   

单一地震事件与多个地震事件的定位方法及应用     

赵金花  李波  陆汉鹏  吴丹桐 《地震地磁观测与研究》2007,28(4):15-19

主要介绍各种地震定位方法,概述各种地震定位方法的基本原理,重点介绍Geiger的经典方法以及在此基础上建立的各种线性方法:单一地震事件定位法与多个地震事件定位法以及对每一种地震定位方法的应用情况,尤其是国内的应用情况做了总结;同时指出各种方法的特点,并进行相应的比较.  相似文献   

关于复合型极端事件的新认识和启示          下载免费PDF全文

余荣  翟盘茂 《大气科学学报》2021,44(5):645-649

近年来,极端天气气候事件频繁发生,且常常表现为多种事件交织形成的复合型极端事件。为了更好地认识复合型极端事件,IPCC AR6基于现有的新证据评估了复合型极端事件的最新研究成果,并取得一些新认识：扩展了有关复合型极端事件的定义,重点围绕高温干旱复合型极端事件、复合洪水和野火,评估了复合型极端事件的变化特征,探讨了复合型极端事件多因子之间的依赖性,对人类活动的影响进行了归因分析并给出了未来可能的变化。这些评估结果丰富了对复合型极端事件的基本认识。但根据现有的评估可以发现,目前在复合型极端事件发生发展机理认识方面还存在不足;同时,未来仍需进一步完善跨学科跨部门跨区域研究,加强对复合型极端事件形成机理、预估及其对生态系统,经济社会影响风险的评估,提高对区域气候变化的适应能力。  相似文献   

Tectonics of the Scandian orogeny and the Western Gneiss Region in southern Norway     

F. H. Koenemann 《International Journal of Earth Sciences》1993,82(4):696-717

Two crust-forming events dominate the Precambrian history of the Western Gneiss Region (WGR) at about 1800–1600 Ma and 1550–1400 Ma. The influence of the Sveconorwegian orogeny (1200–900 Ma) is restricted to the region south of Moldefjord-Romsdalen. A series of anorthosites and related intrusives are present, possibly derived from the now-lost western margin of the Baltic craton that may have been emplaced in the WGR as an allochthonous unit before the Ordovician.The Caledonian development is split into two orogenic phases, the Finnmarkian (Cambrian — Early Ordovician) and the Scandian (Late Ordovician/Early Silurian — Devonian). The lower tectonic units west of the Trondheim Trough may be Finnmarkian nappes ; they were part of the lower plate during the Scandian continental collision. The Blåhö nappe is correlated with dismembered eclogite bodies along the coast. A regional change of nappe transport direction from 090 to 135 marks the initiation of an orogen-parallel sinistral shear component around 425 Ma. The change caused the development of a complex sinistral strike-slip system in the Trondheim region consisting of the Möre-Tröndelag Fault Zone and the Gränse contact. The latter cut the crust underneath the already emplaced Trondheim Nappe Complex, thus triggering the intrusion of the Fongen-Hyllingen igneous complex, and initiating subsidence of the Trondheim Trough, and was subsequently turned from a strike-slip zone into an extensional fault. Minor southward transport of the Trondheim Nappe Complex rejuvenated some thrusts between the Lower and the Middle Allochthon. A seismic reflector underneath the WGR is interpreted to be a blind thrust which subcrops into the Faltungsgraben. During Middle Devonian orogenic collapse, detachment faulting brought higher units, now eroded elsewhere, down to the present outcrop level, such as the Bergen and Dalsfjord nappe and the Old Red basins.  相似文献   

多层递推平稳模型     

汤兆焘  李法然  杨育强  黄玲琳  孙建明 《气象》1994,20(11):40-43

通过对小概率事件历史样本作多层递推迭代，逐次改变引入样本数求取权函数，建立一种平稳统计模式。模式信息容量大，收敛快，克服了常规统计模式的局限性，在灾害性天气客观预报模型应用中取得了明显效果。  相似文献