2014年2月12日新疆于田MW7.0地震源区静态库仑应力变化和地震活动率

2014年2月12日新疆于田M_W7.0地震源区位于巴颜喀拉块体与西昆仑块体的连接部位,东西向拉张构造发育,距离2008年3月21日于田M_W7.1地震震中位置约100 km.根据有限断层地震破裂过程模型,计算了2008年新疆于田地震产生的静态库仑应力变化.此次地震的断层面呈北偏东方向,在断层两端出现3个应力加载区,2014年于田主震位于破裂前端的库仑应力加载区.这一结果表明,2008年于田地震可能对2014年地震事件起到了触发作用.2008和2014年新疆于田地震产生的静态库仑应力变化与余震事件的空间分布具有明显的相关性,大多数余震位于应力加载区,发生在卸载区的余震较少.静态库仑应力变化与余震序列吻合较好.2014年3月21日新疆于田地震之后40天,在北西方向发生M_W5.2强余震,其震中位置的应力增量达到0.63×10⁵Pa.通过比较,发现静态库仑应力变化和地震活动率之间具有较好的相关性.地震活动率较高的区域与静态库仑应力加载区相对应,如康西瓦断裂东段、贡嘎错断裂中段和东北段等区域.     

近断层应力变化快速计算方法及对强余震空间分布的指示意义:以M_w7.9汶川地震为例

构造地震一般由断层摩擦失稳所致.断层内部及周边所累积的剪切形变则通过同震滑动位移得到局部释放.因此,震后断层内部及近断层周边的静态剪切应力变化量的空间分布可通过断层面上的滑动位移分布计算得到.本文采用傅氏变换方法(FTM)计算单一有限断层同震滑移场所形成的静态剪切应力变化分布,近断层两侧的应力变化计算可由波数域内应力近似算法获得.结果表明,FTM快速有效、易于实现,有效地避免了常规应力计算中奇异值的出现.以2008年Mw7.9中国汶川大地震为例,采用前人所得有限断层滑动位移模型,得到了断层面和近断层周边准3D剪切应力分布解,并同主震后中强余震的空间分布特征作了比较.结果表明,大部分的中强余震震源位置处于剪切应力变化值为正的区域,由同震位移所产生的局部应力降峰值和均值大小同应力变化的正值大致相当,从而表明了快速且有效地计算断层内部及近断层附近的应力变化分布可以为主震后强余震发生的潜在区域提供指示意义.需要强调的是,应力变化空间分布特征的获取强烈地依赖于有限断层滑移模型解.有关滑动位移反演解的多解性对应力变化计算结果的影响,本文作了必要的讨论.     

鲁甸6.5级地震发震断层判定及其构造属性讨论

鲁甸6.5级地震是川滇菱形块体南南东向运动在青藏高原东缘与华南地块相互作用边界变形带上发生的一次中等强度地震.尽管野外应急科学考察没有发现明显的地震地表破裂带,但云南昭通防震减灾局局域地震台网记录到的余震条带状分布、震后科学考察获得的地震烈度长轴方位和极震区地震裂缝等显示出发震断层为NW向包谷垴-小河断裂,左旋走滑性质,属大凉山断裂南端部组成部分;库仑应力计算表明,鲁甸地震可对周边活动断层系历史地震空段产生应力加载作用,其地震危险性不容忽视.     

Multiridge Euler deconvolution

Potential field interpretation can be carried out using multiscale methods. This class of methods analyses a multiscale data set, which is built by upward continuation of the original data to a number of altitudes conveniently chosen. Euler deconvolution can be cast into this multiscale environment by analysing data along ridges of potential fields, e.g., at those points along lines across scales where the field or its horizontal or vertical derivative respectively is zero. Previous work has shown that Euler equations are notably simplified along any of these ridges. Since a given anomaly may generate one or more ridges we describe in this paper how Euler deconvolution may be used to jointly invert data along all of them, so performing a multiridge Euler deconvolution. The method enjoys the stable and high‐resolution properties of multiscale methods, due to the composite upward continuation/vertical differentiation filter used. Such a physically‐based field transformation can have a positive effect on reducing both high‐wavenumber noise and interference or regional field effects. Multiridge Euler deconvolution can also be applied to the modulus of an analytic signal, gravity/magnetic gradient tensor components or Hilbert transform components. The advantages of using multiridge Euler deconvolution compared to single ridge Euler deconvolution include improved solution clustering, increased number of solutions, improvement of accuracy of the results obtainable from some types of ridges and greater ease in the selection of ridges to invert. The multiscale approach is particularly well suited to deal with non‐ideal sources. In these cases, our strategy is to find the optimal combination of upward continuation altitude range and data differentiation order, such that the field could be sensed as approximately homogeneous and then characterized by a structural index close to an integer value. This allows us to estimate depths related to the top or the centre of the structure.     

Matching disc and curtain flows in magnetically disrupted accretion discs

An accretion curtain forms when a strongly magnetic star disrupts the inner region of its surrounding disc. It was previously shown that the disc expands vertically due to rapidly growing thermal pressure caused by magnetic heating over a narrow radial transition region inside the corotation radius. This allows material to flow from the disc into a magnetically channelled curtain through which it is transferred to the star. The curtain flow is trans-sonic and sub-Alfvénic, with small distortions of the stellar magnetic field. In the present paper, the disc and curtain flows are matched across the upper boundary of the disc transition region, and this is shown to determine the width of this region as a function of the stellar rotation rate. The sonic point position can adjust to allow steady mass transfer from the disc to the curtain flow. An upper limit can be defined for the rotation period of the star below which a strong magnetic channelling regime applies, with the outer edge of the disruption region lying inside a spherical Alfvén radius. The picture of a thin, magnetically channelled curtain flow fed from a thermally disrupted disc is self-consistent in this regime. A lower limit arises for the stellar angular velocity below which the sonic point merges with the curtain base, resulting in excessive mass loss from the disc which would be inconsistent with a steady solution. This corresponds to a lower limit on the disruption radius as a fraction of the corotation radius. It is noted that the spin-up timescale of the accreting star is significantly less than the lifetime of the system so that typical observed systems should lie in the strong magnetic regime.     

The statistics of a passive scalar in field-guided magnetohydrodynamic turbulence

A variety of studies of magnetised plasma turbulence invoke theories for the advection of a passive scalar by turbulent fluctuations. Examples include modelling the electron density fluctuations in the interstellar medium, understanding the chemical composition of galaxy clusters and the intergalactic medium, and testing the prevailing phenomenological theories of magnetohydrodynamic turbulence. While passive scalar turbulence has been extensively studied in the hydrodynamic case, its counterpart in MHD turbulence is significantly less well understood. Herein we conduct a series of high-resolution direct numerical simulations of incompressible, field-guided, MHD turbulence in order to establish the fundamental properties of passive scalar evolution. We study the scalar anisotropy, establish the scaling relation analogous to Yaglom’s law, and measure the intermittency of the passive scalar statistics. We also assess to what extent the pseudo Alfvén fluctuations in strong MHD turbulence can be modelled as a passive scalar. The results suggest that the dynamics of a passive scalar in MHD turbulence is considerably more complicated than in the hydrodynamic case.     

叠加褶皱研究进展综述

叠加褶皱作为地壳构造变形中一种常见的地质现象, 对于确定多期变形和构造运动期次, 探讨构造演化历史以及内外生矿床的空间分布、形成与变形特征均有重要研究意义。在回顾叠加褶皱研究历史与近年来取得的主要进展基础上, 系统地总结了叠加褶皱几何学与运动学特征, 指出叠加褶皱主要有纵弯褶皱作用、横弯褶皱作用及剪切褶皱作用3种成因机制。在此基础上, 选取典型的叠加褶皱, 剖析了其构造样式及形成机制, 并探讨了叠加褶皱研究的难点与可行研究方法。      

静力触探在工程地质勘察中的应用

本文依据多年来工程地质勘察成果,详细介绍了静力触探应用于地层划分;确定地基土容许承载力;预估单桩竖向承载力;判别在地震动力作用下砂土液化势;地基土空洞探测;确定湿陷性黄土浸水湿陷事故范围;活动断层的工程软弱带的分布与走向。     

油气资源预测统计模型及其应用

松辽盆地北部的油气勘探程度虽然较高,但仍然有一些尚未发现的油气资源。本文在对预测油气资源的分形分布模型和截断帕雷托(TSP)分布模型两种统计模型进行系统研究的基础上,结合油气藏地质规律,通过预测该区未发现的油(气)田数量及其储量规模分布,认为方法可行,结果供参考,并待实践进一步验证。得出主要结论是:分形分布模型是一种预测油气田数量和储量(资源量)的可靠方法,在勘探程度较高的盆地或区带应用效果较好,而在勘探新区应用则有一定难度;截断帕雷托分布模型相对于分形分布模型不很完善,但应用该模型进行油气资源分布预测受具体盆地地质条件的影响较小,具有应用价值。     

Scaling law of the reduced magnetic helicity in fast streams

The reduced magnetic helicity is a quantity related to the handedness of the magnetic field fluctuations. In the present paper we study the scaling law of the reduced magnetic helicity in fast streams in the solar wind by using high-resolution magnetic field data by the Ulysses spacecraft. We show that at high frequencies both the left-hand and the right-hand helicity survives, implying that there is no predominance of a single sign. In addition, the scaling law of the magnetic helicity exhibits a strong dependence on the data set analyzed and we do not observe any universal behavior.