板内大震原地准周期复发间隔的概率分布

以中国大陆大震原地复发资料为基础,采用比较合理的方法确定了板内大震在其活跃期内原地准确周期复发的概率密度函数,所得结果表明,板内大震在重复行为上具有板间特征地震相类似的分布特征,两者的差异在于,板内大震复发间隔的变分系数ＣＯＶ为０．２６,而板间特征地震的该值为０．２１５,即板内大震的重复间隔相对稍显离散。     

内蒙古赵井沟钽铌矿床成矿作用探讨——来自天河石化、钠长石化花岗岩年代学、岩石地球化学的证据

内蒙古武川县赵井沟钽铌多金属矿床是近年来华北板块北缘新发现的大型稀有金属矿床,然而前人对该矿床的形成时代以及构造背景存在较大争议.本文以与成矿关系密切的天河石化花岗岩和钠长石化花岗岩为研究对象,开展了岩相学、岩石地球化学、岩浆和热液锆石LA-ICP-MS U-Pb年代学及Lu-Hf同位素的研究,探讨了岩浆源区性质和成岩...     

Detrital-zircon geochronology of the Jurassic coal-bearing strata in the western Ordos Basin,North China: Evidences for multi-cycle sedimentation

The western Ordos Basin(WOB), situated in a tectonic transition zone in the North China Craton, acts as an excellent example for studying the Mesozoic intraplate sedimentation and deformation in Asia. In this study, U-Pb ages for 1203 detrital zircons of 14 sandstone samples collected from 11 sections are presented to unravel the sediment source locations and paleogeographic environments of the Early-Middle Jurassic coal-bearing Yan'an Formation in the WOB. Data show that there are five prominent age groups in the detrital zircons of the Yan'an Formation, peaking at ca. 282 Ma, 426 Ma, 924 Ma, 1847 Ma, and2468 Ma. Samples from the northern, middle, and southern parts of the WOB contain these five age categories in various proportions. In the northern region, the Yan'an Formation exclusively contains Early Permian detrital zircons with a single age group peaking at 282 Ma, matching well with the crystallizing ages of the widespread Early Permian granites in the Yinshan Belt to the north and the Alxa Block to the northwest. While in the southern region, the Yan'an Formation mainly contains three groups of detrital zircons, with age peaks at 213 Ma, 426 Ma, and 924 Ma. These zircon ages resemble those of the igneous rocks in the Qilian-Qinling Orogenic Belt to the south-southwest. Samples in the middle region, characterized by a mixture age spectrum with peaks at 282 Ma, 426 Ma, 924 Ma, 1847 Ma and 2468 Ma, are previously thought to have mixed derivations from surrounding ranges. However, by referring to the detrital-zircon age compositions of the pre-Jurassic sedimentary successions and combining with paleontological and petrographic analysis, we firstly propose that the sediments of the Yan'an Formation in the middle region were partly recycled from the Triassic and Paleozoic sedimentary strata in the WOB.The occurrence of recycled sedimentation suggests that the Late Triassic-Early Jurassic intraplate compressional deformation was very intense in the WOB, especially for regions in front of the Qilian Orogenic Belt.     

Intraplate seismicity of the Pacific Basin, 1913–1988

We establish here a comprehensive database of intraplate seismicity in the Pacific Basin. Relocation and analysis of 894 earthquakes yield 403 reliable intraplate earthquakes during 1913–1988. These numbers do not include earthquake swarms, which account for another 838 events. Most of the remainder (304 events) are actually plate boundary earthquakes that have been erroneously located in intraplate regions. A significant number occur in recent years when location capabilities should have guarded against this situation. Relocations involve a careful linear inversion ofP andS arrivals, accompanied by a Monte Carlo statistical analysis. We have also attentively removed the high number of clerical errors and nuclear tests that exist in epicenter bulletins.A geographical examination of the relocated epicenters reveals several striking features. There are three NW-SE lineaments north of the Fiji Plateau and in Micronesia; diffuse seismicity and incompatible focal mechanisms argue against the southernmost, discussed byOkal et al. (1986) andKroenke andWalker (1986), as the simple relocation of the Solomon trench to the North. Besides another striking lineament, along the 130°W meridian, there is also a strong correlation between seismicity and bathymetry in certain parts of the Basin. In the Eastcentral Pacific and Nazca plates there are many epicenters on fracture zones and fossil spreading ridges, and hot spot traces like the Louisville, Nazca and Cocos Ridges also display seismicity.     

The relationship betweenin situ strain relaxation and outcrop fractures in the Potsdam Sandstone,Alexandria Bay,New York

Summary In situ strain was measured by overcoring foil-resistance strain gauge rosettes bonded to five outcrops of Potsdam Sandstone near Alexandria Bay, New York. Strain relaxation magnitude and orientation correlated with the area of the intact outcrop outlined by intersecting vertical fractures. The maximum expansion occurred at the outcrop with the largest area between intersecting fractures. Outcrops with more than one set of longer, open fractures or more complicated fracture patterns have lower recoverable strains. Strain relaxation was lowest next to a postglacial pop-up. The orientation of the pop-up indicated relief of an ENE directed compression, the direction also observed as the maximum expansion at the outcrop yielding the largest strain relaxation.Lamont-Doherty Geological Observatory Contribution No. 2456.     

从大陆磁异常特征论板块内部地震成因

首先通过对海洋磁异常与大陆磁异常的对比,说明了大陆磁异常的特征及大陆内部结构和构造的复杂性。进而以华北地区为例,对航磁异常进行带通滤波和视磁化强度反演等数据处理,揭示了大陆地壳内部垂向分层、横向分块的结构特征。结合地震地质、人工地震测深及深部流体等方面的研究,论述了板内地震的生成是由于陆内不同构造块体间相对运动、碰撞、摩擦、应力积累,能量释放的推论。     

Using high resolution data to reveal depth-dependent mechanisms that drive land subsidence: The Venice coast, Italy

Recent research has provided a high-resolution map that depicts the effect of land subsidence on the Venice coastal plain of Italy. The map, which covers the decade of 1992 to 2002, was obtained by an innovative “Subsidence Integrated Monitoring System” (SIMS), which efficiently merges the different displacement measurements obtained by high precision-leveling, differential and continuous Global Positing System data (GPS), and Synthetic Aperture Radar (SAR)-based interferometry. The displacement rates exhibit significant spatial variability, ranging from a slight 1 to 2 mm/yr uplift, to a serious subsidence of more than 10 mm/yr. This paper aims to describe the many natural and anthropogenic mechanisms that drive the pattern of the ground displacement. The movement sources are presented based on their depth of occurrence. Deep causes act at depths generally greater than 400 m below m.s.l. (mean sea level), and are recognizable in the movement of the pre-Quaternary basement. Medium causes act at depths between 400 and 50 m below m.s.l., and include geological features, such as a major presence of compressible clay layers in the southern and northern portions of the study area and groundwater withdrawals, mainly in the north-eastern coastland and western mainland. Shallow causes, i.e. those occurring from a depth of 50 m up to the ground surface, are related to the architecture and geomechanical properties of the Pleistocene and Holocene deposits, which are more thick and compressible approaching the littoral belt; geochemical compaction, due to the increasing salt concentration in the clayey sediments; and oxidation of the outcropping organic soils drained by land reclamation. These two latter factors primarily involve the southern portion of the Venice coast. The building loads in newly developed areas also cause local compaction of shallow deposits. We conclude that the consolidation of Holocene deposits and anthropogenic activities (groundwater withdrawal, land reclamation, and urban land use) are the major factors that contribute to the present land subsidence in the Venice coastland.     

长白山火山的起源和太平洋俯冲板块之间的关系

近年来，尽管不同学科通过不同手段对长白山火山进行过广泛研究，然而，目前人们对它的起源仍不清楚。利用全球地震层析成像和区域层析成像结果，综合分析了长白山火山的起源。结果表明，它的起源既不同于夏威夷等板内热点火山，也不同于日本等岛弧火山，而是一种与太平洋俯冲板块在地幔转换带内的滞留和深部脱水等过程密切相 关的弧后板内火山。     

A Probabilistic Approach for Identifying Independent Remote Compressions in an Intraplate Region: The?Iberian Chain (Spain)

The discrimination between distinct remote compressions and multiple local stress deviations within a single compressive stress field has been carried out in the central-eastern Iberian Chain, by using structural criteria, computing palaeostress directions, identifying and ‘filtering’ stress deviations, and analysing time relationships. A probabilistic analysis based on a systematic comparison of real and expected frequencies of coexistence of two compressions is applied by means of the χ ² Test. This allows us to identify those tectonic compressions that behave as independent events from the probabilistic point of view. The results suggest that among five initially defined compression directions only three can be considered as representative of distinct (although partially superposed) externally applied intraplate stress fields: Iberian s.l. (NE-SW), Betic s.l. (NW-SE), and Pyrenean (N-S to NNE-SSW).     

由空间大地测量得到的太平洋板块现今构造运动与板内形变应变场

推导了板块的弹性运动方程.根据太平洋板块(PCFC)上空间大地测量的观测结果,建立了PCFC的弹性运动模型,该模型与板块实际运动状态的符合程度明显地优于刚体运动模型.研究表明：PCFC现今旋转的角速度比过去3Ma的平均值大0.037°/Ma;在PCFC内部存在明显的水平形变,在15°S以北和204.5°E以西地区存在一致的向西形变,北西与南西方向的形变速率分别为0.8～3.5 mm/a与1.0～3.4 mm/a;在板块的东南区存在一致的向东形变,北东与南东方向的形变速率分别为1.5～1.8 mm/a与2.8～9.1 mm/a.PCFC内部水平应变场的空间变化是有规律的,在PCFC的西北部,主压应变轴为NW-SE方向,主压应变率大于主张应变率;在PCFC的东南部,主压应变轴为NE-SW方向,主张应变率大于主压应变率;PCFC的东南边界是扩张边界,边界附近的主张应变率最大（平均为1.51×10-9/a）,主张应变轴基本上与洋中脊的扩张方向一致;PCFC的西北边界是俯冲边界,边界附近的主压应变率最大（平均为0.75×10-9/a）,主压应变轴基本上与太平洋板块的俯冲方向一致.