巴林左旗-阿鲁科尔沁旗5.9级地震前地震活动异常特征     

曹井泉  刘芳  朱学健  腾喜林 《东北地震研究》2004,20(4):1-7

对2003年8月16日巴林左旗阿鲁科尔沁旗间5．9级地震前震源区附近地震活动图像和地震学参数研究结果表明，震前5～1年震源区附近地震活动异常平静，而外围(150km≤△≤300km)区地震活动显著增强；震前2年左右，震源区附近地震学参数异常比较明显，异常项数比40％；震前1．0～0．5年地震学参数异常明显减弱，异常项数比仅10％。可见，地震学短期异常不明显。  相似文献   

Frequency domain modal analysis of earthquake input energy to highly damped passive control structures     

Izuru Takewaki 《地震工程与结构动力学》2004,33(5):575-590

A new complex modal analysis‐based method is developed in the frequency domain for efficient computation of the earthquake input energy to a highly damped linear elastic passive control structure. The input energy to the structure during an earthquake is an important measure of seismic demand. Because of generality and applicability to non‐linear structures, the earthquake input energy has usually been computed in the time domain. It is shown here that the formulation of the earthquake input energy in the frequency domain is essential for deriving a bound on the earthquake input energy for a class of ground motions and for understanding the robustness of passively controlled structures to disturbances with various frequency contents. From the viewpoint of computational efficiency, a modal analysis‐based method is developed. The importance of overdamped modes in the energy computation of specific non‐proportionally damped models is demonstrated by comparing the energy transfer functions and the displacement transfer functions. Through numerical examinations for four recorded ground motions, it is shown that the modal analysis‐based method in the frequency domain is very efficient in the computation of the earthquake input energy. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

A Preliminary Analysis of Relations Between Tectonic Deformation of Sedimentary Cover and Basement in Kuqa Depression     

Liu Jie 《中国地震研究》2004,18(4):406-416

Study of seismic activity in the Kuqa area enables us to infer some possible active faults in basement from the epicentral distribution on different profiles. The relations between active faults in the basement and surface structures are analyzed and the difference between sedimentary cover and basement in their deformation characteristics and the genesis are discussed. The following conclusions have been drawn : ( 1 ) the epicentral distribution indicates that, the east Qiulitag and south and north Qiulitag deep faults in the basement correspond to the east and west Qiulitag anticlines, respectively. Moreover, deep faults also exist beneath the Yiqiklik and Yaken anticlines. It indicates that the formation of surface structures is controlled by deep structures; (2) A NE-trending strike-slip fault develops along the line from the western termination of Yiqiklik structure to Dongqiu Well 5 and a NW-trending active fault on the western side of Baicbeng. The two active faults across the tectonic strike are the main causes for tectonic segmentation of the Kuqa depression and possibly the cause for the middle segment (Kuqa-Baicheng) of the depression to be more shortened than both its eastern and western terminations; (3) The difference between the sedimentary cover and basement in their deformation characteristics depends mainly on the different properties of media between them.The lithospheric strength of the basement in the basin is fairly high, which determines the basement deformation to be mainly of brittle fracture seismic activity. While the strength of sedimentary cover is low, where there exist weak thin layers, such as coal and gyps. Under the effect of strong tectonic compression, the sedimentary rocks may undergo strong viscous or plastic flow deformation; meanwhile, an aseismic detachment may take place along the weak layers.  相似文献   

下辽河平原新近系地下水开采的动态变化特征     

王卫东  宋庆春 《华北地质》2004,27(3):144-148

新近系地下淡水是下辽河三角洲地区的盘锦市和辽河油田主要供水水源。地下水处于封闭到半封闭环境，包括明化镇组(Nm)和馆陶组(Ng)两个含水岩组。天然状态下，地下水位接近或高于地表；开采条件下，地下水位逐年下降，形成区域性降落漏斗，地下水流场均发生显著变化，形成汇向开采区的向心流场。开采明化镇组地下水为主的盘东水源地，开采初期水位下降速率为1.61～5．19m／a，至1996年降至0．63～1．03m／a；馆陶组地下水为主的各水源地，开采初期水位下降速率为2．10～4．21m／a，至1996年减至1．49～2．05m／a。这是由于地下水流场变化，导致明化镇成水体内侵和下移所致，该地地下水中Cl^-的不断增高也证明了这一点。至1998年。平面上，成水体每年增加3．18km^2，盘东水源南部，成水体内侵速率已达每年220m。垂向上成水体年下移速率一般每年0．5～1．67m。进行新近系地下水动态特征和演化趋势研究，将为合理开发利用宝贵的淡水资源提供科学依据。  相似文献   

Nation states, ideological power and globalisation: can geographers catch the boat?     

Martin Jones  Rhys Jones 《Geoforum》2004,35(4):409-424

After a period of considerable and sustained hegemony, many commentators have argued that contemporary processes of globalisation are acting as a challenge to nation state sovereignty. The paper argues that geographers need to focus on the ways in which the nation state continues to act, albeit in a modified manner, within the era of globalisation. This might help to position geography within globalisation debates, which--according to Dicken [Geographers and `globalization': (yet) another missed boat? forthcoming, Transactions of the Institute of British Geographers, 2004]--we have not been centrally involved in. Drawing on the work of Michael Mann, we focus on a neglected dimension of state power--namely, its ideological form--as a means of exploring how the nation state is being differentially re-engineered under globalisation. Using Mann's classification of forms of ideological organisation, we deploy three vignettes in order to demonstrate the evolving nature of ideological power within the contemporary UK State.  相似文献   

Triaxial stress state deep in orogenic belts: an example from Turkey     

T. Masuda  S. Nakayama  N. Kimura  K. Onodera  A. Okamoto 《Journal of Structural Geology》2004,26(12):2203-2209

A rare metachert pebble containing amphibole grains with microboudin structures in a wide range of orientations provides an opportunity to perform stress analysis in two orthogonal orientations on the foliation surface. The sample was analysed by the microboudin method to infer the triaxial stress state during microboudinage. Stress parameters proportional to the far-field differential stress were determined for sodic amphibole grains in the two orientations. The ratio of the stresses in the two orthogonal orientations (σ₁−σ₂)/(σ₁−σ₃) was calculated to be 0.64, indicating that σ₂ lies closer to the midpoint between σ₁ and σ₃ than to σ₃.  相似文献   

Thermo-mechanical structure beneath the young orogenic belt of Taiwan     

Kuo-Fong Ma  Teh-Ru Alex Song 《Tectonophysics》2004,388(1-4):21

We investigate the thermo-mechanical properties beneath the young orogenic belt of Taiwan by constructing a shear strength profile from a vertical stratified rheological structure. The stratified rheological structure is estimated based on the recently developed thermal structure and its likely composition. Subduction–collision in the young orogenic belts and the thick accretionary wedge make a significant contribution to the growth of sialic crust in the hinterland. The sialic bulk crust not only results in a low seismic velocity but also produces weak crust in the hinterland. The earthquake depth–frequency distribution in the foreland and hinterland correlates very well with the regimes of the brittle/ductile transition revealed in the strength profile. Our results show that the observed two-layer seismicity in the foreland is due to a moderate geotherm and an intermediate mafic bulk composition; while single-layer seismicity in the hinterland is due to its felsic bulk composition. In the foreland, the mechanically strong crust (MSC) and the mechanically strong lithosphere (MSL) coincide with frequent seismicity. The shallow MSC in the hinterland is consistent with the 20- to 25-km seismicity occurring there. The total lithospheric integrated strength (LIS) in the hinterland is only about half of that in the foreland, suggesting a weak lower crust and lithosphere mantle in the hinterland. The results confirm that the earthquake cutoff depth is a proxy for temperature. The calculated decrease of effective elastic thickness (EET) from the orogenic margin (foreland) to the center (hinterland) is consistent with the results of flexure modeling in most orogenic belts. Due to the weak LIS in the hinterland, crustal thinning and rifting may occur in the future. Our results, thus, suggest that the mechanical structure is also closely related to the composition and is not directly reflected in the thermal structure.  相似文献   

宁夏香山荒漠草原区植物群落多样性时空特征   总被引：10，自引：0，他引：10  

尚占环  妙爱兴  龙瑞军  辛明  郭旭生  马文志 《山地学报》2004,22(6):661-668

采用多个多样性指数对宁夏香山荒漠草原区植物群落多样性时间、空间动态进行分析。结果表明，该地区群落时、空动态特征不明显。长期过度放牧导致环境恶化，生境碎化，这些作用的长期性、循环性是造成物种、群落格局与原有时、空动态规律相悖的主要因素，这些因素消除了物种或群落在时间梯度上应有的变化规律。干旱山地物种在长期进化过程中成功的发展了对环境的适应机制，环境的波动性强烈导致了群落多样性在原来消长动态基础上的复杂化，也使多样性动态机制复杂化。应用多种指数数学模型对研究对象进行综合评价，能够真实地反映群落多样性动态。  相似文献   

Regions and sustainable development: regional planning matters   总被引：1，自引：0，他引：1  

Graham Haughton  Dave Counsell 《The Geographical journal》2004,170(2):135-145

This paper looks at how the term 'sustainable development' has been used in the process of regional plan making over the past decade. It emphasizes the differing geographies of these debates within England, in terms of how sustainable development has been used to justify different types of approach in different parts of the country. Both drawing on and challenging recent work on state theory, the paper argues the need to see regional planning as a part of a multi-scalar governance system, whose importance should not be underestimated.  相似文献   

Upper Pleistocene and Holocene paleosalinity and trophic state changes in relation to sea level variation in Rocha Lagoon, southern Uruguay     

F. García-Rodríguez  D. Metzeltin  P. Sprechmann  R. Trettin  G. Stams  L.F. Beltrán-Morales 《Journal of Paleolimnology》2004,32(2):117-135

Paleolimnological data are presented on trophic development in relation to sea level variation in Rocha Lagoon, a 72 km² coastal lagoon in southern Uruguay. Using sediment cores that extended to ∼20,000 yr BP, analyses of grain size, organic matter, carbonate, total carbon, nutrients, and diatoms allowed us to infer changes in trophic state and paleosalinities, which were closely related to Holocene relative sea level variation. Higher trophic states were observed during regressive events, most probably due to increases in runoff and erosion as regressions progressed. Diatom Association Zones (DAZ) were identified in both cores. Those DAZ corresponding to transgressive events were dominated by marine/brackish taxa and relatively low organic matter and nutrient values, while those DAZ corresponding to regressive events showed increases in brackish/freshwater diatoms and both organic matter and nutrients. Although the lagoon formed after the first Holocene marine transgression, our data indicate the existence of a marine/brackish aquatic system during upper Pleistocene (i.e., before 15,000 yr BP), but by ∼20,000 yr BP, the system was still likely to be a semi-arid terrestrial system.  相似文献