临猗5.0级地震前后品质因子值变化特征研究     

王卫东  张永志  杜长娥 《地球科学与环境学报》2005,27(1):70-71,79

利用西安数字地震遥测台网记录的数字地震资料，采用P波初动半周期残差法求得1998年7月临猗5．0级地震前后不同路径的Q(品质因子)值变化，发现在地震发生前Q值为87～203，震后Q值为67～164，震前震中区附近出现明显的高Q值异常。结果表明，地震前的高Q值异常可以作为地震预测的一种手段。  相似文献   

1979年夏季青藏高原大气热量水平输送的周期振荡事实     

陈万隆  刘玉英 《南京气象学院学报》1991,14(2):226-233

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岩体三维节点偶对分析及其应用          下载免费PDF全文

王思敬  张菊明 《地质科学》1991,(3):277-287

本文讨论了节点偶对分析的三维扩展。节点偶对分析是针对摩擦滑动节理单元的约束边界进行的序列矢量判定。在三维节理单元的分析中,几何约束和相应的力学判据极为复杂,采用节点偶对等效结合力方法才能迎刃而解。文中对三维转向节理模型的分析得到合理的结果,它表明本文所提出的方法可成功地应用于节理岩体的有限元分析。  相似文献   

Holocene activity of the Scilla Fault, Southern Calabria: Insights from coastal morphological and structural investigations     

L. Ferranti  C. Monaco  D. Morelli  F. Antonioli  L. Maschio 《Tectonophysics》2008,453(1-4):74

Integration of on-land and offshore geomorphological and structural investigations coupled to extensive radiometric dating of co-seismically uplifted Holocene beaches allows characterization of the geometry, kinematics and seismotectonics of the Scilla Fault, which borders the eastern side of the Messina Strait in Calabria, Southern Italy. This region has been struck by destructive historical earthquakes, but knowledge of geologically-based source parameters for active faults is relatively poor, particularly for those running mostly offshore, as the Scilla Fault does. The  30 km-long normal fault may be divided into three segments of  10 km individual length, with the central and southern segments split in at least two strands. The central and northern segments are submerged, and in this area marine geophysical data indicate a youthful morphology and locally evidence for active faulting. The on-land strand of the western segment displaces marine terraces of the last interglacial (124 to 83 ka), but seismic reflection profiles suggest a full Quaternary activity. Structural data collected on bedrock faults exposed along the on-land segment provide evidence for normal slip and  NW-SE extension, which is consistent with focal mechanisms of large earthquakes and GPS velocity fields in the region. Detailed mapping of raised Holocene marine deposits exposed at the coastline straddling of the northern and central segments supplies evidence for two co-seismic displacements at  1.9 and  3.5 ka, and a possible previous event at  5 ka. Co-seismic displacements show a consistent site value and pattern of along-strike variation, suggestive of characteristic-type behaviour for the fault. The  1.5–2.0 m average co-seismic slips during these events document M_e  6.9–7.0 earthquakes with  1.6–1.7 ka recurrence time. Because hanging-wall subsidence cannot be included into slip magnitude computation, these slips reflect footwall uplift, and represent minimum average estimates. The palaeoseismological record based on the palaeo-shorelines suggests that the last rupture on the Scilla Fault during the February 6, 1783 M_w = 5.9–6.3 earthquake was at the expected time but it may have not entirely released the loaded stress since the last great event at  1.9 ka. Comparison of the estimated co-seismic extension rate based on the Holocene shoreline record with available GPS velocities indicates that the Scilla Fault accounts for at least  15–20% of the contemporary geodetic extension across the Messina Strait.  相似文献   

Microbially mediated carbonates in the Holocene deposits from Sarliève, a small ancient lake of the French Massif Central, testify to the evolution of a restricted environment     

JEAN-GABRIEL BRÉHÉRET  AGATHE FOURMONT  JEAN-JACQUES MACAIRE  PHILIPPE NÉGREL† 《Sedimentology》2008,55(3):557-578

Both the mineralogy and facies of lacustrine bio‐induced carbonates are controlled largely by hydrological factors that are highly dependent upon climatic influence. As such they are useful tools in characterizing ancient lake environments. In this way, the study of the sedimentary record from the small ancient Sarliève Lake (Limagne, Massif Central, France) aims to reconstruct the hydrological evolution during the Holocene, using petrographical, mineralogical and geochemical analyses. The fine‐grained marls, mainly calcitic, display numerous layers rich in pristine Ca‐dolomite, with small amounts of aragonite, which are clearly autochthonous. As these minerals are rather unusual in the temperate climatic context of western Europe, the question arises about their forming conditions, and therefore that of the lacustrine environment. Ca‐dolomite prevails at the base of the sequence as a massive dolomicrite layer and, in the middle part, it builds up most of the numerous laminae closely associated with organic matter. Scanning electron microscope observations reveal the abundance of tiny crystals (tens to hundreds of nanometres) mainly organized as microspheres looking like cocci or bacilli. Such a facies is interpreted as resulting from the fossilization of benthic microbial communities by dolomite precipitation following organic matter consumption and extracellular polymeric substance degradation. These microbial dolomites were precipitated in a saline environment, as a consequence of excess evaporation from the system, as is also suggested by their positive ?¹⁸O values. The facies sequence expresses the following evolution: (i) saline pan, i.e. endorheic stage with a perennial lowstand in lake level (Boreal to early Atlantic periods); (ii) large fluctuations in lake level with sporadic freshening of the system (Atlantic); (iii) open lake stage (sub‐boreal); and (iv) anthropogenic drainage (sub‐Atlantic).  相似文献   

Distinct climate change synchronous with Heinrich event one, recorded by stable oxygen and carbon isotopic compositions in stalagmites from China   总被引：2，自引：0，他引：2  

Houyun Zhou  Jianxin Zhao  Michael K. Gagan  Jun Yan 《Quaternary Research》2008,69(2):306-315

Uranium-series dating of oxygen and carbon isotope records for stalagmite SJ3 collected in Songjia Cave, central China, shows significant variation in past climate and environment during the period 20-10 ka. Stalagmite SJ3 is located more than 1000 km inland of the coastal Hulu Cave in East China and more than 700 km north of the Dongge Cave in Southwest China and, despite minor differences, displays a clear first-order similarity with the Hulu and Dongge records. The coldest climatic phase since the Last Glacial Maximum, which is associated with the Heinrich Event 1 in the North Atlantic region, was clearly recorded in SJ3 between 17.6 and 14.5 ka, in good agreement in timing, duration and extent with the records from Hulu and Dongge caves and the Greenland ice core. The results indicate that there have been synchronous and significant climatic changes across monsoonal China and strong teleconnections between the North Atlantic and East Asia regions during the period 20-10 ka. This is much different from the Holocene Optimum which shows a time shift of more than several thousands years from southeast coastal to inland China. It is likely that temperature change at northern high latitudes during glacial periods exerts stronger influence on the Asian summer monsoon relative to insolation and appears to be capable of perturbing large-scale atmospheric/oceanic circulation patterns in the Northern Hemisphere and thus monsoonal rainfall and paleovegetation in East Asia. Climatic signals in the North Atlantic region propagate rapidly to East Asia during glacial periods by influencing the winter land-sea temperature contrast in the East Asian monsoon region.  相似文献   

Decoupling of stalagmite-derived Asian summer monsoon records from North Atlantic temperature change during marine oxygen isotope stage 5d   总被引：2，自引：0，他引：2  

Houyun Zhou  Jianxin Zhao  Chuan-Chou Shen  Yuexing Feng  Huazheng Guan  Chen-Feng You 《Quaternary Research》2008,70(2):315-321

The Asian monsoon is an important component of the global climate system. Seasonal variations in wind, rainfall, and temperature associated with the Asian monsoon systems affect a vast expanse of tropical and subtropical Asia. Speleothem-derived summer monsoon variation in East Asia was previously found to be closely associated with millennial-scale change in temperature in the North Atlantic region between 75 and 10 ka. New evidence recovered from East Asia, however, suggests that the teleconnection between summer monsoon in East Asia and temperature change in the North Atlantic region may have significantly reduced during 120 to ~ 110 ka, a period directly after the full last interglaciation and corresponding roughly to marine oxygen isotope stage 5d. This reduction may be due to the low ice volume in the North Hemisphere at that time, which makes the millennial-scale change in temperature in the North Atlantic region less effective in influencing the Asian summer monsoon. This is important for investigating the mechanisms controlling the Asian summer monsoon and the paleoclimatic teleconnection between East Asia and the North Atlantic region, and for predicting monsoon-associated precipitation in East Asia under a global-warming trend.  相似文献   

Morphological analysis of the drainage system in the Eastern Alps   总被引：2，自引：1，他引：1  

Jrg Robl  Stefan Hergarten  Kurt Stüwe 《Tectonophysics》2008,460(1-4):263-277

We study the morphology of the major rivers draining the Eastern Alps to test whether the active tectonics of this part of the orogen is reflected in the shape of channel profiles of the river network. In our approach we compare channel profiles measured from digital elevation models with numerically modelled channel profiles using a stream power approach. It is shown that regions of high stream power coincide largely with regions of highest topography and largest uplift rates, while the forelands and the Pannonian Basin are characterised by a significantly lower stream power. From stream power modelling we conclude that there is young uplift at the very east of the Eastern Alps, in the Bohemian Massif and in the Pohorje Range. The impact of the Pleistocene glaciations is explored by comparing properties of rivers that drain in proximal and distal positions relative to the ice sheet during the last glacial maximum. Our analysis shows that most knick points, wind gaps and other non-equilibrium features of catchments covered by ice during the last glaciations (Salzach, Enns) can be correlated with glacial processes. In contrast the ice free catchments of the Mur and Drava are characterized by channels in morphological equilibrium at the first approximation and are showing only weak evidence of the strong tectonic activity within these catchments. Finally, the channel profiles of the Adige and the divide between the upper Rhine and Danube catchments differ significantly from the other catchments. We relate this to the fact that the Adige and the Rhine respond to different base levels from the remainder of the Eastern Alps: The Adige may preserve a record from the Messininan base level change and the Rhine is subject to the base level lowering in the Rhine Graben.  相似文献   

太湖平原西北部全新世古河道沉积特征及环境演变   总被引：1，自引：0，他引：1  

舒军武  王伟铭  陈晔 《地层学杂志》2008,32(2):146-152

粒度、磁化率定量数据分析在判明第四系沉积物的来源、识别沉积分异作用、解译古沉积相和环境方面有着重要作用。对太湖平原西北部卜弋桥ZK01钻孔上部全新统如东组进行了粒度和磁化率测试分析,结合该孔孢粉成果,揭示研究区全新世古河道沉积环境和气候明显经历了3个阶段:1)11000—9500cal.aBP,沉积物主要由粉砂组成,粒度证据表明水动力条件较强,孢粉证据显示该阶段气候较温暖湿润;2)9500—3900cal.aBP,沉积物砂组分含量大幅增加,粒度资料显示古河道水动力明显增强,孢粉植被表明该时期处于全新世大暖期,气候暖湿稳定;3)3900cal.aBP以来,粉砂组分在沉积物中占优势,粒度结果表明该阶段水动力显著减弱,孢粉资料和磁化率证据表明研究区自该阶段特别是后期以来逐步出现了明显的人类活动迹象。  相似文献   

微型氢化物发生装置在冷原子吸收分光光度法测汞中的应用     

赵延庆 《岩矿测试》2008,27(1):69-70

采用微型氢化物发生装置-冷原子吸收分光光度法测定了焊锡料及纽扣电池中的汞。在酸性介质中,用硼氢化钾将汞离子还原为汞原子,用载气将汞蒸气导入石英管,原子吸收分光光度计在波长253.7 nm处进行测定。选择了实验条件,对共存离子的干扰等进行了考察。方法的检出限为0.34 ng/mL,11次测定的相对标准偏差(RSD)小于6%,加标回收率为94.4%~104.7%。  相似文献