The geological and geodynamic evolution of the eastern Black Sea basin: insights from 2-D and 3-D tectonic modelling   总被引：1，自引：0，他引：1  

D. J. Meredith  S. S. Egan 《Tectonophysics》2002,350(2)

Subsidence mechanisms that may have controlled the evolution of the eastern Black Sea have been studied and simulated using a numerical model that integrates structural, thermal, isostatic and surface processes in both two- (2-D) and three-dimensions (3-D). The model enables the forward modelling of extensional basin evolution followed by deformation due to subsequent extensional and compressional events. Seismic data show that the eastern Black Sea has evolved via a sequence of interrelated tectonic events that began with early Tertiary rifting followed by several phases of compression, mainly confined to the edges of the basin. A large magnitude (approximately 12 km) of regional subsidence also occurred in the central basin throughout the Tertiary. Models that simulate the magnitude of observed fault controlled extension (β=1.13) do not reproduce the total depth of the basin. Similarly, the modelling of compressional deformation around the edges of the basin does little to enhance subsidence in the central basin. A modelling approach that quantifies lithosphere extension according to the amount of observed crustal thinning and thickening across the basin provides the closest match to overall subsidence. The modelling also shows that deep crustal and mantle–lithosphere processes can significantly influence the rate and magnitude of syn- to post-rift subsidence and shows that such mechanisms may have played an important role in forming the anomalously thin syn-rift and thick Miocene–Quaternary sequences observed in the basin. It is also suggested that extension of a 40–45 km thick pre-rift crust is required to generate the observed magnitude of total subsidence when considering a realistic bathymetry.  相似文献   

Post-mid-Cretaceous eastern North Sea evolution inferred from 3D thermo-mechanical modelling   总被引：1，自引：0，他引：1  

Lykke Gemmer  Sren B. Nielsen  Mads Huuse  Holger Lykke-Andersen 《Tectonophysics》2002,350(4):105-342

The Late Cretaceous–Cenozoic evolution of the eastern North Sea region is investigated by 3D thermo-mechanical modelling. The model quantifies the integrated effects on basin evolution of large-scale lithospheric processes, rheology, strength heterogeneities, tectonics, eustasy, sedimentation and erosion.

The evolution of the area is influenced by a number of factors: (1) thermal subsidence centred in the central North Sea providing accommodation space for thick sediment deposits; (2) 250-m eustatic fall from the Late Cretaceous to present, which causes exhumation of the North Sea Basin margins; (3) varying sediment supply; (4) isostatic adjustments following erosion and sedimentation; (5) Late Cretaceous–early Cenozoic Alpine compressional phases causing tectonic inversion of the Sorgenfrei–Tornquist Zone (STZ) and other weak zones.

The stress field and the lateral variations in lithospheric strength control lithospheric deformation under compression. The lithosphere is relatively weak in areas where Moho is deep and the upper mantle warm and weak. In these areas the lithosphere is thickened during compression producing surface uplift and erosion (e.g., at the Ringkøbing–Fyn High and in the southern part of Sweden). Observed late Cretaceous–early Cenozoic shallow water depths at the Ringkøbing–Fyn High as well as Cenozoic surface uplift in southern Sweden (the South Swedish Dome (SSD)) are explained by this mechanism.

The STZ is a prominent crustal structural weakness zone. Under compression, this zone is inverted and its surface uplifted and eroded. Contemporaneously, marginal depositional troughs develop. Post-compressional relaxation causes a regional uplift of this zone.

The model predicts sediment distributions and paleo-water depths in accordance with observations. Sediment truncation and exhumation at the North Sea Basin margins are explained by fall in global sea level, isostatic adjustments to exhumation, and uplift of the inverted STZ. This underlines the importance of the mechanisms dealt with in this paper for the evolution of intra-cratonic sedimentary basins.  相似文献   

REE Geochemistry of the Lead—Zinc Ores from the Jinding Lead—Zinc Deposit,Lanping,Yunnan   总被引：3，自引：1，他引：3  

牟传龙  余谦  张立生 《中国地球化学学报》2002,21(1):57-64

Nineteen volcanic and magmatic rock samples were collectecd from the Jinding leadzinc deposit and its surrounding areas in Yunnan.The ICP and AES analyses,feferred to the previous results,show that the metal minerals and altered rocks in the Jinding lead-zinc deposit display a decreasing trend of ∑REE from the early to late stages of mineralization,and similarities in REE distribution patterns,indicating that the ore fluids are characterized by high LREE enrichment,markedly negative δCe anomaly and slight δEu anomaly.These REE distribution paterns exhibit striking similarities to those of the Pliocene trachyte in the study area,both of which are similar in ∑REE,LREE/HREE ratio,δEu and δCe.The ore fluids besides the basin fluids in the deposit are also closely related to those associated with Pliocene trachyte magmas.  相似文献   

内蒙古色尔腾山山前断裂(乌句蒙口-东风村段)的断层活动与古地震事件   总被引：6，自引：0，他引：6  

杨晓平  冉勇康  胡博  郭文生 《中国地震》2002,18(2):127-140

通过对色尔腾山山前断裂乌句蒙口 -东风村段的遥感资料解释、野外地质地貌考察 ,并通过对重点地段的古地震探槽开挖 ,获得了该断裂段晚更新世晚期以来的垂直位移速率是 0 88～ 1 83mm a ,全新世中期以来的垂直位移速率是 0 89mm a。通过 2个大型探槽的开挖、古地震事件分析和相关堆积物的断代研究 ,以及用逐次限定方法分析整个断层段上的古地震事件 ,认定该断裂段上全新世以来发生了 5次古地震事件 :事件 1发生在距今 90 0 0± 130 0年 ,事件2发生在距今 6 5 0 0± 5 0 0年 ,事件 3发生在距今 5 5 70年左右 ,事件 4发生在距今 4 2 0 0± 30 0年 ,事件 5发生在距今 32 5 0± 2 5 0年。晚更新世晚期到距今 1万年之间 ,古地震事件很不完整。全新世以来的 5次古地震事件表现出一定的丛集特征。最早的一丛事件发生在距今 890 0年左右 ,第2丛发生在距今 6 5 0 0～ 5 70 0年之间 ,第 3丛事件发生在距今 32 5 0～ 4 2 0 0年之间。第 1丛与第 2丛古地震事件之间间隔为 2 4 0 0年左右 ,而第 2丛与第 3丛古地震事件之间仅间隔 15 70年左右。距今 32 5 0年以来 ,该断裂段上还没有发生过错断地表的地震事件 ,已经超出了古地震丛之间的重复间隔。因此 ,它是色尔腾山前活动断裂带上具备潜在危险的一个活动断裂段。  相似文献   

2000年4月29日内乡ML4.7级地震前潢川地电异常变化     

张俊山  胡卫建  王志敏  张佩  谢健健  刘丽君 《华南地震》2002,22(3):65-70

2000年4月29日11时54分，河南省南阳市内乡县马山口镇与镇平县寺山乡之间发生一次ML4.7级地震。地震前3天，潢山台视电阻率ρs异常较为明显。分析了此次异常与内乡ML4.7级地震的关系，认为此次异常很有可能是内乡ML4.7级地震的短临前兆异常。当观测台站与震源位于同一构造带时，即便离震中较远，地电阻率对地震异常反映仍较灵敏，且与构造带同一走向的测向尤为明显。  相似文献   

The use of modern statistical theories in the assessment of earthquake hazard, with application to quiet regions of eastern North America     

G. R. Dargahi-Noubary   《Soil Dynamics and Earthquake Engineering》2002,22(5)

It is generally accepted that both deterministic and statistical approaches are useful for the characterization of earthquake hazard. Although the most reliable estimates of seismic hazard can only be based on an improved understanding of the earthquake mechanism, efficient utilization of the appropriate methods provided by recent statistical theories is also important in seismic risk analysis. This is especially true in regions where the connection between seismicity and geologic structure is tenuous at best. We are particularly interested in developing better statistical treatments of data for regions with little known seismic activity. To this end, we have applied three statistical methods to the historical record of seismicity in relatively quiet regions of eastern North America. These are: (1) the threshold method for tail inference, a new theory for modeling earthquakes with sizes above a given threshold, (2) the ‘bootstrap’ technique in which the characteristics of an unknown population are simulated by replacing the true population by an estimated one, and (3) a technique to estimate the number of earthquakes below a given size, in order to compensate for the under-reporting of small earthquakes in most catalogs. A combination of these techniques has been used to estimate the probabilities of future large earthquakes for the regions studied. Because of limitations imposed by existing catalogs, the size estimate used has been maximum intensity.  相似文献   

ELF propagation parameters for uniform models of the Earth–ionosphere waveguide     

Vadim C. Mushtak  Earle R. Williams 《Journal of Atmospheric and Solar》2002,64(18)

Uniform models for the Earth–ionosphere cavity are considered with particular attention to the physical properties of the ionosphere for the extremely low frequency (ELF) range. Two consistent features have long been recognized for the range: the presence of two distinct altitude layers of maximum energy dissipation within the lower ionosphere, and a “knee”-like change in the vertical conductivity profile representing a transition in dominance from ion-dominated to electron-dominated conductivity. A simplified two-exponential version of the Greifinger and Greifinger (1978) technique widely used in ELF work identifies two slopes in the conductivity profile and, providing accurate results in the ELF communication band (45–75 Hz), simulates too flat a frequency dependence of the quality factor within the Schumann resonance frequency range (5–40 Hz). The problem is traced to the upward migration, with frequency increasing, of the lower dissipation layer through the “knee” region resulting in a pronounced decrease of the effective scale height for conductivity. To overcome this shortcoming of the two-exponential approximation and still retain valuable model analyticity, a more general approach (but still based on the Greifinger and Greifinger formalism) is presented in the form of a “knee” model whose predictions for the modal frequencies, the wave phase velocities and the quality factors reasonably represent observations in the Schumann resonance frequency range.  相似文献   

喀什"奇异震群"与构造地震的对比研究     

夏爱国  刘永廷  缑兰兰 《内陆地震》2002,16(3):193-204

20 0 1年 11月 14、 15日新疆喀什台记录到 86次振动事件 (“奇异震群”事件 )。为识别其性质 ,应用波谱分析、偏振分析等方法 ,对该事件和同范围构造地震的地震波特征进行了对比研究 ,发现 :(1)喀什“震群”的全波列衰减比构造地震的全波列衰减快很多 ;(2 )与构造地震的速度谱相比 ,“震群”的频谱相对较为“集中”,而构造地震的则较为“发散”;(3)“震群”位移谱的拐角频率和卓越频率均较构造地震的相应量高出一倍多 ,且离散较小。通过对喀什“奇异震群”这些特征进行分析研究 ,认为这一事件极有可能是人工事件  相似文献   

泾阳4.8级地震的构造背景   总被引：12，自引：1，他引：12       下载免费PDF全文

王卫东 《地震工程学报》2002,24(2):145-149

1998年1月5日烃阳Ms 4.8地震是陕西省近40年来发生的最大一次地震。研究了此次地震的构构背景和地球物理场特征。  相似文献   

甘青地区中晚全新世植被变化与人类活动   总被引：5，自引：5，他引：5  

安成邦  陈发虎  冯兆东 《干旱区地理》2002,25(2):160-164

史前时期人类对环境的影响是近几年来国际研究的热点。在甘青地区，全新世的孢粉资料比较多。但在中晚全新世，该区人类对环境的影响作用及其程度仍不清楚，许多孢粉分析资料中并没有充分考虑人类活动的影响。本文选取孢粉分辨率较高、代表性较好的青海湖、兰州、秦安大地湾三地的资料，着重研究了其中乔木成分的变化。分析发现，孢粉组合中乔木成分的变化与气候变化的趋势并不一致。通过对考古及历史资料的分析，笔者认为，该区的植被很早就受到人类活动的影响。自全新世中期，本区植被中的乔木成分波动下降。5000－3000a BP期间，史前农业对植被的影响较大。3000－2000a BP期间，植被略有恢复。2000a BP以后，人为影响加剧，植被中乔木成分迅速下降。研究者认为，依赖孢粉资料重建中晚全新世的气候变化历史应当慎重。  相似文献