水库地震主震发生时间的预测

水利工程对水库地震的抗震设防要求事先对水为地震进行预测。预测内容包括蓄水后诱发地震的危险性（可能性、）最大震级、最大震的地占紧及不库地震对场址地震动参数的影响。除主震时间的预测外，本文第一作者都曾提出过初步的预测方法。本文认为，水库地震前震波速比异常、非线性灰色模型以及前震系列回归等方法，是预测主震时间的有前途的方法。     

云南地区双震型地震序列中第二主震的前震识别

本文通过对双震型地震序列的地震波动力学特征的研究，提出了识别双震中第二主震前震的可能性。结果表明、在双震第一主震发生后，序列地震的Ｐ波垂直分量初动一致时，可依据波形来识别第二主震的前震；而初动不一致时有三种情况：１、两组初动中有一组Ｐ、Ｓ波振幅比仍保持为过原点的直线而另一组离散，２、两组初动的振幅比分别为过原点的直线；３、两组初动的振幅比共同组成过原点的直线，对前两种情况可识别第二主震的前震，最后一种情况难以识别。总体达６０－７０％的可识别率。     

用地震活动性指数A（b）等资料判断图像以后有无主震及震级大小

用 A(b)指数判断图象以后有无主震,其效果颇好。A(b)指数能将有主震 M_L≥5.0与有主震 M_L≤4.7(或无主震)区别开来。再加地震活动的范围、强度资料的配合,能判断主震的大小。此方法的资料自检准确率陆地达96%,震例检验的准确率也高。这样的判断,对用图象作地震预报有重要的作用。     

1995年择捉岛近海地震：前震,主震和余震的联合重新定位及对地震成？…

千岛群岛１９９５年１２月３日择捉岛近海Ｍｗ７．９地震有明显的前震活动。用修改的联合震源定位法,我们同时重新定位了前震、主震和余震,从大地震成核过程的观点详细地研究了前震活动。重新定位的地震分布和它们的震源机制说明,１９９５年择捉岛近海地震是北美和太平洋板块间的板间地震。它的震源区与１９５８年择捉岛近海地震（Ｍｗ８．３）和１９６３年乌鲁普岛近海地震（Ｍｗ８．５）的震源区重叠。主震发生前９天,第１个震     

地震波动力学特征在宁蒗─盐源地区地震序列早期判断中的应用

通过对宁蒗─盐源地区各类地震序列在３天和７天内地震波动力学特征的研究，表明该地区前震序列的地震在垂直分量上Ｐ波初动一致，且Ｐ、Ｓ波最大振幅比值稳定，呈过原点的直线，其振幅比值较低，而早期前震序列振幅比值较高。双震型地震序列出现两组初动，第一主震的余震振幅比不稳定，但第二主震的前震振幅比仍保持呈过原点的直线，利用地震特特征可望区分第一主震的余震和第二主震的前震。主余震地震序列的地震振幅比不稳定。应用地震波动力学特征作为地震序列的早期判断方法，可在３天和７天内对宁蒗─盐源地区的前震、双震型地震序列作出判断，在３天内对主余震序列作出判断。     

云南地区3次6级间歇性双震第二主震的前震特征分析

分析大姚6．2，6．1级间歇性双震地震序列的地震波、地震活动变化，以类比方法分析了同震型的1976年盐源-宁蒗6．7，6．4级地震序列，1971年普洱6．7，6．2级地震序列，寻求第二主震的前震活动特征，结果表明：大姚6．2级与盐源-宁蒗6．7级序列中均出现一组P，S波振幅比为直线的前震；双震序列在第一主震后20～60d内，出现3，4级地震频度增高与b值、h值偏离余震衰减准同步异常的现象，第二主震临震前数天出现3，4级地震平静，与第二主震时间间隔仅2～9h，相距震中8km内发生3级显著地震。为预测预报间歇性双震序列的第二主震提供了一定判据。     

长期加速的前震活动可预示西希腊弧强震发生的时间

西希腊弧（WHA）1899年（Ms＝6．6）和1947年（Ms＝7．0）两次主震发生之前数十年，震中周围半径100km范围内的前震（Ms≥5．2）发生率，一般可以说是处在加速过程中的。经历较长期水平非常低的前震活动（阶段I）之后，主震前数月前震活动过程以最终的快速加速而达到高潮（阶段Ⅱ），最后的两个月则处于平静（阶段Ⅲ）。这三个阶段与地壳形变和用膨胀模式预测的主震前一些前兆的三个阶段非常吻合。资料与幂次律方程拟合得很好，这与一般的短期前震和建造人工湖出现的情况相似。以前的WHA的强震破裂带位置意味着该弧段的东部是最可能发生下次强震的地方。从1966年以来此处就已进行着地震活动的加速过程，这也与1899和1947年地震之前的情况类似。对比早先地震与目前预料发生的地震在幂次律曲线上的变化，表明后者的发生已推迟了3－8个月。假设长期加速的前震活动是WHA地段地震构造的一个特色，我认为WHA下次破裂的孕育已进入高度成熟阶段，在今后的几个月里，该区很可能发生一次地震。     

主震100年后可发生余震

一位地震学家说,余震通常在主震后数月内发生在同一断层段上,但是,主震100年后,在附近的断层上也可能发生余震。美国地质调查局的地震学家琼斯(LucileJones)说:“根据定义把地震排成序列,我们将最大的地震称之为主震。任何发生在最大地震之前的地震都是前震,任何发生在最大地震之后的地震都是余震。”     

根据地震频度衰减预报地震的工作细则

近几年来,我们曾经研究了根据地震频度衰减预报地震的方法。这一方法的基本概念是这样的:假定有一地震序列,我们也已经有了这个系列的资料(包括各次地震的时间、震级及震中位置)。问题是现在的地震系列是前震系列还是主震、余震系列呢?如果是前震系列,我们便预报今后还有主震发生,有的情况下还可以大略估算出主震的震级;如果地震系列经判断是主震-余震系列,则可以计算最大余震震级,供预报时参考。     

前震发生的模型

我们建立了一个前震和前震序列发生的模型。假设前震及主震都是由于早已存在的裂纹的突然合并而发生的。如果裂纹端部的应力强度因子超过某临界值时就会发生合并。在亚临界状态下，每条裂纹都由于应力的侵蚀准静态经历着加速延伸，一直到临界状态时止，裂纹增长就是在此时刻变成灾变性的。当主震临近时，前震的发生率增加，可用时间的幂次律函数对它描述。幂次律中的指数与裂纹尺度、间距和破裂强度的分布无关。这种普遍意味着前震图象应当是预测大震发生时间的有用标志。可是我们发现能量释放图象之间有很大的差异。尽管如此，如果人们有描述障碍体强度和几何分布的先验资料，则根据前震序列中地震的震级来预测大震的震级还是有些希望的。     

用集集主震记录研究近断层强震记录的基线校正方法

从集集主震记录中选取有代表性的246个台站的记录作为数据集。在总结国内外基线校正方法的基础上,提出以下校正步骤:(1)初步判定记录中是否包含永久位移信息以便选用不同的校正方法。(2)以积分位移时程的末端平稳为标准,来确定积分速度时程末端拟合出的最优直线斜率作为校正量,去校正原始加速度时程,从而保留永久位移信息。永久位移等值线结果与GPS测量结果大体相符。根据校正结果推测认为:瞬变后保持或扩张或部分回弹,可能是决定永久位移形态的主要物理机制。     

Preliminary estimation for the focal mechanisms of 1996 Lijiang main shock in Yunnan Province and studies of related problems

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Zone of main contribution to the measured signal for a circular current loop source and receiver on the surface of a conductive half‐space

The electric and magnetic fields generated by an individual horizontal current ring induced inside a homogeneous conductive half‐space, originating from an external large circular loop source of current in the presence of a flat half‐space, are deduced. A check of self‐consistency for these expressions led to the known general functions for these fields due to the same external source in the presence of that medium. The current rings’ mutual coupling related to the magnetic field's radial component is thoroughly analysed and its specific members are presented. The existence of a relatively small zone inside the half‐space responsible for the main contribution for the signal measured at the observation point, with the source and receiver on the ground surface, is made evident. For increasing values of frequency, at a given transmitter‐receiver (T–R) configuration, this zone shrinks and its central point moves away from a maximum depth of about 30% and horizontal distance of nearly 85%, of the T–R separation, to a point very close to the receiver position. The coordinates of the central point of this zone of main contribution are provided as approximated functions in terms of the induction number .     

Dependence of the aftershock flow on the main shock magnitude

Previously, we predicted and then observed in practice the property of aftershocks which consists in the statistically regular clustering of events in time during the first hours after the main shock. The characteristic quasi-period of clustering is three hours. This property is associated with the cumulative action of the surface waves converging to the epicenter, whereas the quasi-period is mainly determined by the time delay of the round-the-world seismic echo. The quasi-period varies from case to case. In the attempt to find the cause of this variability, we have statistically explored the probable dependence of quasi-period on the magnitude of the main shock. In this paper, we present the corresponding result of analyzing global seismicity from the USGS/NEIC earthquake catalog. We succeeded in finding a significant reduction in the quasiperiod of the strong earthquakes clustering with growth in the magnitude of the main shock. We suggest the interpretation of this regularity from the standpoint of the phenomenological theory of explosive instability. It is noted that the phenomenon of explosive instability is fairly common in the geophysical media. The examples of explosive instability in the radiation belt and magnetospheric tail are presented. The search for the parallels in the evolution of explosive instability in the lithosphere and magnetosphere of the Earth will enrich both the physics of the earthquakes and physics of the magnetospheric pulsations.     

电离层电导对地球磁层顶和舷激波尺度的影响

本文在如下假定下分析电离层电导对地球磁层顶和舷激波尺度的影响：（1）对电离层采用球壳近似,Pedersen电导Σ_P均匀,Hall电导为零;（2）地磁偶极矩处于正南方向,行星际磁场（IMF）只有南向分量（B_z<0）.磁层顶和舷激波的尺度分别由它们与GSE坐标系三个轴的交点,即日下点、晨昏侧翼点和南北顶点的地心距离表征.对给定的太阳风条件、B_z和Σ_P,通过三维全球MHD模拟获得系统的准定态.结果表明,在大约1～5 S范围内,Σ_P值显著影响磁层顶和舷激波的尺度,而在该范围之外则几乎没有影响.随着Σ_P的增加,磁层顶和舷激波整体向外扩张,前者的扩张程度低于后者,以至磁鞘区的范围扩大.磁层顶的侧翼点的位置随Σ_P的变化与B_z的幅度有关：在弱南向IMF情况下磁层顶的侧翼点随Σ_P的增加向内移动,而在强南向IMF情况下则向外移动.上述结果表明,在构建磁层顶和舷激波的经验模型时,有必要计入电离层电导的影响.     

一个关于临界地城的临界区域判别的方法

由临界地震的概念和外推Ｂｏｗｍａｎ等人关于孕育未来的地震半径的思想,发展出一个临界圆重叠方法来地寻找未来强震的临界区域位置,模拟实验的对比检验表明这种方法是有效的,使用主震前一定时间内地震目录,这个方法能找出临界区域,而未来震中位置将位于临界区域内或其边缘。使用新西兰和中国新疆南部的中强震目录检验,该方法可以在震前较准确地定位出强城的临界区域位置,使用中国１９９５年至１９９９年８月的小震目录,给出     

Effects of the interplanetary magnetic field clock angle on the shape of bow shock

Using the global magnetohydrodynamics(MHD) simulation model, we investigated the effects of the interplanetary magnetic field(IMF) clock angle on the shape of bow shock, including its rotational asymmetry and subsolar point. For general northward IMF( z component Bz 0), the rotational symmetry of the bow shock is broken by the effects of fast magnetosonic Mach number(Mms), and the cross-sectional line of the bow shock is an ellipse with the semi-major axis along the direction perpendicular to the IMF. The ratio or D-value between semi-major and semi-minor axis can be used to illustrate the extent of asymmetry of the bow shock. On the basis of the multiple parameters fitting, we obtain the changing relationship of both semi-axes with the clock angle and the distance away from the Earth. For general southward IMF(Bz 0), the cross sectional line of the bow shock is highly asymmetrical under the multiple effects of magnetopause and Mms. The effects of IMF clock angle on subsolar point depend mainly on the changing subsolar point of magnetopause as an obstacle. The distance of subsolar point of bow shock from the Earth increases with the increasing IMF clock angle for Bz 0, and decreases with the increasing IMF clock angle for Bz 0.     

云南省地震观测数据库软件的开发与实现

根据云南省地震信息“十五”项目的规范和要求,设计并开发了云南省地震观测数据库系统软件。软件包括前兆模拟观测数据库管理软件（由数据源绘图检查、数据入库与管理、数据库绘图检查组成）、前兆模拟观测数据库文件上报软件和地震速报目录数据库管理软件。数据库管理系统的建立,解决了地震观测数据入库问题和数据库完整性问题,可为分析预报人员和地震科研人员提供及时、准确的数据。     

地震频度曲线非线性特征与主震后有后续地震的预测

本文对川滇地区1988年以来MS>5.0级地震前后ML≥3.0级地震活动的强度和频度变化进行了分析。结果认为,主震前ML≥3.0级地震活动的强度和频度曲线有一个非线性趋势增强的变化过程,主震后ML≥3.0级地震活动的强度和频度曲线仍然保持上升的非线性增强,曲线上升的非线性增强对整个区域一定时间段内有后续地震的判断给出了短期异常信息。     

Silting patterns in the reservoirs of small- and medium-sized earthen check dams in humid subtropical monsoon regions

Silting of reservoirs is a ubiquitous process whenever water is impounded. Despite substantial work on the rates of silting, the spatial pattern of silting in reservoirs is not clearly understood. While it is anticipated that the variability of silting increases with decreasing reservoir size, not much is known about siltation in subtropical humid regions affected by monsoon rainfall. This paper presents the initial results of geomorphic analysis of six earthen check dams in the Shiwalik foothills of the Himalayas (India) in areas that are inhabited by high proportions of disempowered populations. These check dams include three small-sized dams (Dhamala-II, Rel Majra and Sukhomajri-II) and three medium-sized dams (Bunga-I, Parachh-II and Siswan). Field data were collected from each reservoir. The methods used included spatial interpolations of bed depth and silt thickness in each reservoir, Structure from Motion photogrammetry to extract multiple channel cross-sections from photographic scans along tributary mouths, texture analysis of bed and bank materials, and visual observations of hill slopes around the check dams. Based on this study, silt tended to concentrate either in the middle portion of the reservoir or near the dam; however, silt accumulation did not always occur along the dam or in the deepest portion of the reservoirs. Areas located downstream from these check dams are heavily used for various human activities and the channel network has almost been eliminated. While these earthen check dams may be cost-effective tools for water conservation in economically marginalized areas, if abandoned, these structures may pose a physical hazard to downstream communities. © 2019 John Wiley & Sons, Ltd. © 2019 John Wiley & Sons, Ltd.