Relationship between Crustal 3D Density Structure and the Earthquakes in the Longmenshan Range and Adjacent Areas     

ZHANG Jisheng GAO Rui  ZENG Lingsen  LI Qiusheng  GUAN Ye  HE Rizheng  WANG Haiyan  LU Zhanwu 《《地质学报》英文版》2009,83(4):740-745

Abstract: This paper presents the 3D density structure of crust in the Longmenshan range and adjacent areas, with constraints from seismic and density data. The density structure of crust shows that the immense boundary plane of density distribution in relation to the Longmeshan fault belt is extended downward to ~80 km deep. This density boundary plane dips towards the northwest and crosses the Moho. With the proximity to the Longmenshan fault belt, it has a larger magnitude of undulation in the upper and middle crust levels. Density changes abruptly across Longmeshan fault belt. Seismic data show that most of the earthquakes in the Longmenshan area after the 2008 Ms8.0 Wenchuan Earthquake occurred within the upper to middle crust. These earthquakes are clearly distributed in the uplifted region of the basement. A few of them occurs in the transitional zone between the uplifted and subsided areas. But most of the earthquakes distributes in transitional zone from subsided to uplifted areas in the upper and middle crust where relatively large density changes occurr The 3D density structure of crust in the Longmenshan and adjacent areas can thus help us to understand the pattern of overthrusting from the standpoint of deep crust and where the earthquakes occurred.  相似文献   

Abnormal Phenomena Recorded by Several Earthquake Precursor Observation Instruments Before the Ms 8.0 Wenchuan,Sichuan Earthquake   总被引：1，自引：0，他引：1  

OUYANG Zuxi  ZHANG Hongxun  FU Zizhong  GOU Bo  JIANG Wali 《《地质学报》英文版》2009,83(4):834-844

Abstract: The paper introduces the anomalies observed by digital tiltmeter, cross-fault deformation meter, 4-component borehole strainmeter and geothermometer before May 12, 2008, Ms8.0 Wenchuan earthquake, Sichuan. The digital tiltmeter installed in the epicentral region in Shifang County recorded the tilt anomalies 15 days before the earthquake with variation amplitude of 3.7 times larger than the annual deviation of 2007. The cross-fault deformation meter installed at Zimakua station on the Xianshuihe-Anninghe fault zone detected displacement anomaly occurring since 2006 with the variation amplitude exceeding the cumulative value of the last ten years. Five borehole strainmeter stations in the Chongqing section of Three Gorges Reservoir area observed unconventional strain changes occurring in the period from May 1 through 12, 2008. Among them, the strainmeter at Wanzhou station recorded the great compression strain rate on the EW component at 14:00 o'clock of May 10, and the anomaly amplitude was so large that the instrument output exceeded its dynamic range, corresponding to a level of ~104 nanostrains. The geothermometers installed in Xi’an, Chongqing and Xichang recorded the sudden temperature changes from November 2007 to January 2008 with the variation amplitudes several times larger than the ordinary deviation. The above phenomena and the criteria for distinguishing the anomalies from background fluctuations are discussed in this paper.  相似文献   

不规则网土壤测量在水系沉积物异常查证中的应用     

苑凤华  潘建  陈馥  曹立敏  梁春华  周亚杰 《吉林地质》2009,28(3):95-99

在大兴安岭森林沼泽景观区,植被茂盛、土壤表层腐殖质发育,且通视条件差,运用传统的规则网土壤测量方法进行1/5万水系沉积物异常查证,工作周期长、劳动强度大;采用不规则网土壤测量方法进行异常查证,取得了快速评价异常、追踪异常源,缩短找矿周期的效果。  相似文献   

Magmatic history and geophysical signature of a post-collisional intrusive center emplaced near a crustal-scale shear zone: the Plechý granite pluton (Moldanubian batholith,Bohemian Massif)     

Kryštof Verner  Jiří Žák  Jaroslava Pertoldová  Josef Šrámek  Jiří Sedlák  Jakub Trubač  Patricie Týcová 《International Journal of Earth Sciences》2009,98(3):517-532

The Plechy pluton, southwestern Bohemian Massif, represents a late-Variscan, complexly zoned intrusive center emplaced near the crustal-scale Pfahl shear zone; the pluton thus provides an opportunity to examine the interplay among successive emplacement of large magma batches, magmatic fabric acquisition, and the late-Variscan stress field associated with strike-slip shearing. The magmatic history of the pluton started with the emplacement of the porphyritic Plechy and Haidmühler granites. Based on gravity and structural data, we interpret that the Plechy and Haidmühler granites were emplaced as a deeply rooted, ∼NE–SW elongated body; its gross shape and internal fabric (steep ∼NE–SW magmatic foliation) may have been controlled by the late-Variscan stress field. The steep magmatic foliation changes into flat-lying foliation (particularly recorded by AMS) presumably as a result of divergent flow. Magnetic lineations correspond to a sub-horizontal ∼NE–SW finite stretch associated with the divergent flow. Subsequently, the Třístoličník granite, characterized by steep margin-parallel magmatic foliation, was emplaced as a crescent-shaped body in the central part of the pluton. The otherwise inward-younging intrusive sequence was completed by the emplacement of the outermost and the most evolved garnet-bearing granite (the Marginal granite) along the southeastern margin of the pluton. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.  相似文献   

Intrusion versus inversion—a 3D density model of the southern rim of the Northwest German Basin     

Filiz Bilgili  Hans-Jürgen Götze  Roman Pašteka  Sabine Schmidt  Ron Hackney 《International Journal of Earth Sciences》2009,98(3):571-583

An unsolved problem of regional importance for both the evolution and structure of the Northwest German Basin is the existence or non-existence of the so-called Bramsche Massif. Explaining the nature of this massif and the cause of a related strong, positive Bouguer anomaly (Bramsche Anomaly) is critical. In the study described here, we tested an existing “intrusion model” against a newer “inversion model” in the southern Northwest German Basin. In the intrusion model, the strongly-positive Bouguer anomaly represents the gravity effect of an intrusion at depths between 6 and 10 km. More recent interpretations invoke tectonic inversion rather than intrusion to explain increased burial and the low level of hydrocarbon maturity found in boreholes. We tested these different interpretations by constructing 3D forward density models to 15 km depth. The intrusion model was updated and adjusted to incorporate recent data and we also modelled pre-Zechstein structures using different scenarios. The final model has a very good fit between measured and modelled gravity fields. Based on currently available seismic and structural models, as well as borehole density measurements, we show that the positive Bouguer anomaly cannot be modeled without a high-density, intrusive-like body at depth. However, further in-sight into the crustal structures of the Bramsche region requires more detailed investigations. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.  相似文献   

煤层气组分浓度异常及其地球化学成因     

兰凤娟  ;秦勇  ;林玉成 《中国煤炭地质》2009,(4):27-30

煤层气组分浓度异常蕴含着丰富的地球化学成因信息,某些有害组分的异常浓度往往会对矿工人身健康造成影响。为此,基于相关文献和资料从重烃浓度异常、氧化物气体浓度异常、硫化氢浓度异常三个方面总结了国内外研究进展,分析了关于煤层气组分浓度异常地球化学成因的种种假说,认为目前对煤层气组分浓度异常的成因尚欠深入理解,有必要结合具体实例开展解剖研究,并从新的视角予以探讨。  相似文献   

河北张百湾中生代盖层下隐伏磁铁石英岩型铁矿床的勘查条件   总被引：2，自引：2，他引：0  

李健  贾大成  白雪山  李永占  裴尧  宋运红 《世界地质》2009,28(2):187-192

矿床勘查条件是寻找隐伏铁矿的基础。通过对河北张百湾隐伏铁矿勘查的, 归纳了寻找隐伏磁铁石英岩型铁矿的勘查条件。原始含矿建造是寻找隐伏铁矿的基础条件, 盖层的厚度和产状及岩性对寻找隐伏铁矿起限制作用, 断裂构造对隐伏铁矿起破坏作用, 但简单的差异性升降对隐伏铁矿勘查的影响程度不大。航磁异常是寻找隐伏铁矿的重要条件, 地面高精度磁异常是寻找隐伏铁矿的充分条件, 而对地面磁测数据的合理处理是了解深部磁性体产状变化和埋深的必要条件。  相似文献   

南巴伦支海磁场异常及其与海底地质结构的对比(英文)          下载免费PDF全文

A.M.Filin  Yu.D.Malyutin  A.N.Ivanenko  N.A.Shishkina 《地学前缘》2009,16(6)

对1986—2001年间巴伦支海南部海洋磁力测量的数据处理结果进行了研究。南巴伦支海底的地磁测量揭示出其复杂多期的地质构造结构,其中以两期分离型的构造为主导:(1)具NW走向的里菲-文德期继承性裂谷构造;(2)NE向转换叠加断层正交系统。晚泥盆世碱性侵入体及其相关的金属矿化作用恰位于这些构造系统的交点上。  相似文献   

位场反演计算的场比值法及在宽城地区磁异常解释中的应用   总被引：1，自引：1，他引：0  

张季生  高锐  管烨  李秋生  李朋武  王海燕  卢占武 《地球学报》2009,30(6):868-872

在磁异常的反演计算中, 为了避免由于选错了磁性体的形状而产生很大的误差, 前人已研究了多种所谓自动反演的计算方法。与传统的方法不同, 用这些方法, 可以同时确定磁性体的几何形状和埋藏深度等参数。但是前人研究的方法需要计算磁异常的三阶导数, 因此所受高频噪声干扰十分严重, 以至于影响到计算结果的可靠性。因此很难用到实际资料处理中。 本文提出的场比值法可以同时确定磁性体的形状和埋藏深度。场比值法通过场比值field-ratio来确定磁性体的形状, field-ratio的物理含义与Euler反褶积公式中的形状因子类似。场比值法的优点是在反演计算中只需要计算磁异常的一、二阶导数, 因此比前人的方法受高频随机干扰小, 可以用于实际资料的处理中。模型实验证明了场比值法的正确性, 在河北省宽城地区用场比值法对磁异常反演计算, 展示了方法的实用性。 关键词: 磁异常; 自动反演; 磁性体形状的判别  相似文献   

ASTER遥感数据蚀变遥感异常提取研究   总被引：14，自引：0，他引：14  

吕凤军  郝跃生  石静  王娟 《地球学报》2009,30(2):271-276

基于ETM+/TM数据提取矿化蚀变遥感异常已趋于成熟, 而利用ASTER(先进星载热发射和反射辐射仪)遥感数据提取矿化蚀变遥感异常鲜有报道。本研究利用USGS波谱数据库中典型蚀变矿物反射率数据, 重建其在ASTER数据中波谱曲线研究表明, ASTER遥感数据可以提取Mg-OH、Al-OH、CO32?和Fe3+离子(基团)信息。热液矿床的蚀变围岩通常含有上述4种离子(基团), 它们的波谱特征是蚀变遥感异常提取的理论依据。本研究利用改进“去干扰异常主分量门限技术流程”, 以河北省承德地区和太行山区为例, 上述离子(基团)信息提取结果与野外实际分布相一致, 表明利用ASTER遥感数据提取上述4种离子(基团)信息是可靠的。  相似文献