大尺度花岗闪长岩试件缓慢破裂过程的倾斜变化

本文叙述了1986年夏季在四川省西昌地震中心站进行的岩石膨胀破裂试验及伴随试件缓慢破裂过程的倾变观测结果。岩石主破裂前的异常倾变及破裂时的倾斜阶跃,较好地印证了实际地壳倾斜观测中记录到的一些现象(地震前兆、同震阶跃等)。文章还对“尺度效应”等问题进行了讨论。     

倾斜扰动--一种可能的有效地震前兆

依据小地震时的倾斜记录和岩石破裂时的应变扰动记录提出，岩石破裂和微小地震可能引起倾斜扰动，这种扰动将可能是大地震的有效前兆。然而，如何区分干扰和前兆扰动还需仔细研究。     

岩石失稳破裂前激发极化效应的初步研究

本文介绍了在压应力作用下观测岩石失稳破裂前激发极化效应的实验方法和主要结果。重点研究了沉积砂岩、矿化灰岩和部分橄榄岩的激发极化特征及其变化规律,讨论了岩石的脆柔性质与破裂前兆的关系。实验结果表明:(1)在压应力作用下,岩石的激发极化效应十分明显,规律性强,变化幅度大;(2)随着压应力的增大,极化率出现以下降为主的有规律性的变化,其幅度可达百分之几到百分之几十;(3)普遍记录到了岩石失稳破裂前的极化率前兆特征——加速下降和急剧上升,其变化形态与岩石的脆柔性质有关。最后,本文对岩石激发极化压应力效应的机理及其在地震预报研究中的应用作了初步探讨。     

岩石破裂中的电子发射

利用G-M计数器和塑料闪烁体探测器在花岗岩单轴压缩破裂实验中首次记录到电子发射,电子能量分别为0.05McV和0.35MeV量级。根据这一结果提出了岩石破裂中出现可见光及其它电磁辐射的理论解释。     

强地震前兆低频波的实验研究

声波透射实验表明，对于板状材料，声音的一部分能量可以透射到空气中。另一部分能量在板中产生简正波，使板产生较大的振幅，在空气中产生能被话筒接收到的声音信号，而信号的简正频率与板的尺寸有关。另外，破裂过程中的声发射实验证实：随着微破裂的集结和裂纹的扩展，所辐射波的频谱会逐渐向低频移动，而且当频率很低时，可以透射出岩石，被话筒接收到。根据尺度相似性原理，推广到野外，强地展前破裂集结可能会辐射出超低频波，这种超低频波不能被常规的地震仪记录到，但可以被超低频传感器或次声接收器记录到。在地震前，产生前兆的源非常复杂，大多数情况下可能并非脆性破裂，而是塑性蠕滑或者有流体的参与。而后两种情况产生的波的周期会更长，而且缺乏脆性破裂所固有的高频成分，这可能就是多数地震前缺乏前震的原因。     

用电子-空穴理论推算汶川MS8.0地震 电磁异常的 “能量源”大小

基于汶川M_S8.0地震前3天记录到的强空间电磁异常的观测事实, 引用岩石压电效应模型和岩石受压产生的电子-空穴理论, 尝试推算和解释汶川地震前产生的显著空间电磁异常现象的“能量源”问题. 结果显示: 在设定汶川M_S8.0地震发震主断层所受最大水平主应力和断层表面积的情况下, 根据理论模型模拟计算得出, 当发震主断层在强压力作用下形成微破裂至宏观破裂发育产生主破裂前, 断层表面积累的电荷带电量为106—107 C, 产生的垂直地-气界面附加电场为107—108 V/m; 主破裂发生时, 断层表面电量可达108 C, 电场强度高达109 V/m, 断层输出电流量级达105 A. 震源区地-气界面电磁场的增强, 一方面引起地面附近大范围电磁观测参数的大幅度突变异常, 另一方面加速震源区上空的气体分子电离, 空气电离增强空气的电导率, 促使电荷快速扩散至电离层高度, 直接引起高空电离层参数的短时突变异常并经空间地震监测卫星记录到.      

伴随岩石破裂的VLF，MF，HF和VHF电磁辐射特性的实验研究

许多国内外学者观测到伴随岩石破裂的电磁辐射现象，但实验结果不能解释实际观测记录的不同步现象，即有的台有异常，有的台没有异常；同一个观测台不同频段的信号也不同时出现．给地震预报工作带来不少困难．本实验结果可以解释不同步现象．实验采用单轴加压岩样直至破裂．不同频段的天线安置在远离岩样２ｍ的不同方位上．采用１４道磁带机同步记录岩样破裂全过程的电磁信号．实验结果表明：①岩样在主破裂过程中，４种频段都记录到了信号，但不同频率出现的时间有时不同步；②主破裂发生时刻电磁辐射强度最大，但不同方位信号的强度不同     

破裂的定标律

早期的一些论文在很宽的尺度范围内讨论了破裂的标度问题。种种统计幂函数关系常常可以成功地用来描述碎块的大小分布及其形状，表明破裂具有一种标度不变的过程。但是，这是建立破裂形状对碎块大小分布的分数维没有任意影响的条件之下。对于岩石破碎破裂能量的新定标律，可由分形几何学概念及Ｇｒｉｆｆｉｔｈ能量平衡准则导出。     

伴随岩石破裂的VLF，MF，HF和VHF电磁辐射特性的实验研究.

许多国内外学者观测到伴随岩石破裂的电磁辐射现象，但实验结果不能解释实际观测记录的不同步现象，即有的台有异常，有的台没有异常；同一个观测台不同频段的信号也不同时出现．给地震预报工作带来不少困难．本实验结果可以解释不同步现象．实验采用单轴加压岩样直至破裂．不同频段的天线安置在远离岩样2 m的不同方位上．采用14道磁带机同步记录岩样破裂全过程的电磁信号． 实验结果表明:① 岩样在主破裂过程中，4种频段都记录到了信号，但不同频率出现的时间有时不同步；② 主破裂发生时刻电磁辐射强度最大，但不同方位信号的强度不同.      

岩石破裂时光辐射的实验研究

岩石破裂时光辐射现象是近来不少学者感兴趣的问题,它具有多方面的理论及实际意义。孙正江等用胶片直接感光方法证明了光辐射的存在,B.T.Brady和A.Rowell等用光学摄谱法得到了岩石破裂时辐射的光谱特性和照片。我们用粒子探测方法,研究了岩石破裂时光辐射特性及其与其它物理效应的相关问题。这种方法是利用光电倍增管接收光子,通过光电效应转换成电脉冲信号,经放大后输入多道脉冲分析器进行脉冲幅度分析。它的优点是对瞬间微弱闪光非常灵敏,不仅可以记录可见光而且可记录非可见     

岩石破裂时电磁辐射的机理研究

本文提出了岩石破裂时的电磁辐射是裂纹尖端电荷随着裂纹加速扩展运动所产生的假说.应用断裂力学方法推导了岩石破裂时初始裂纹长度与裂纹扩展加速度的关系,并计算了其速度和加速度值.根据破裂岩石的电子发射理论,解释了裂纹尖端带电荷的现象.利用岩石在单轴压缩致裂过程中记录到的近场电磁辐射的实验结果,计算了裂纹扩展时裂纹尖端的电荷量和远场电磁辐射强度.通过对电磁辐射波谱分析的研究,得到岩石破裂时电磁辐射频率上限的估计值.最后对岩石破裂时出现的声光电磁现象在理论上作了统一的定性的解释.     

高压直流输电对大柏舍台地电场观测干扰的分析

在分析高压直流输电对地电场观测产生干扰原因的基础上, 应用大柏舍台近年来受高压直流输电干扰的地电场数据分析受高压直流干扰时的地电场变化、 入地电流、 换流站接地极与台址关系, 计算了高压直流输电干扰时台址岩体裂隙优势方位。 结果表明: 地电场变化形态仅在高压输电入地电流开始注入和停止注入时产生大幅度的跃变; 高压直流输电干扰时电场强度与入地电流大小成正比, 与台址到换流站接地极的距离的平方成反比; 应用地电场潮汐变化前10阶谐波振幅计算台址岩体裂隙优势方位的方法有甄别高压直流输电干扰的效果。     

Experimental study of the features of VLF, MF, HF and VHF electromagnetic radiation accompanying rock fracture

In order to investigate the physical mechanism of seismo-electromagnetic signals, many scholars from China and other countries have carried out laboratory and field experiments of rock samples by loading them up to fracture in recent ten-odd years. In each of these experiments, the phenomenon of electromagnetic radiation was observed during the process of rock sample fracture. However, the experimental results can not explain the non-synchronous electromagnetic radiation in actual observation records. In these records, some stations displayed anomalies but some others did not, and the signals of different frequency bands observed by the same station did not occur simultaneously. This has brought about many difficulties to the application of electromagnetic radiation in earthquake prediction. The experimental result of this paper can explain the phenomenon of non-synchronous electromagnetic radiation. In the experiment of this paper, rock samples are uniaxially compressed up to fracture. The antennas of different frequency bands are installed two meters away from the rock sample in different directions. The electromagnetic signals during the whole process of rock sample fracture are recorded synchronously by a 14-channel tape recorder. The experimental results are as follows: (1) signals of the four frequency bands: VLF, MF, HF and VHF, are all recorded during the main fracturing process of rock samples, but signals of different frequencies may somtimes occur non-synchronously; (2) the intensity of electromagnetic radiation is the highest at the moment when the main fracture occurs, but signals in different directions are of different intensities. The above results are consistent with the non-synchronous electromagnetic radiation observed in real earthquakes. It seems possible to predict the orientation of future seismic source by the electromagnetic method of the LF or VLF frequency bands. Contribution No. 95A0075, Institute of Geophysics, SSB, China. The paper is translated by Prof.Jie-Fan HUANG, Peking University from the Chinese into English version.     

Experimental study on the mechanism of non-synchronism of seismo-electromagnetic radiation precursors

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基于人工源的甚低频电磁波空间传播特征统计分析

利用2005年1月至2010年11月DEMETER卫星记录的NWC发射站的VLF电场功率谱数据,采用指数拟合的方法,分析了VLF电磁波在卫星高度激发的电场空间分布和衰减特征.研究结果表明:(1)VLF电场在发射站上空及其磁共轭区有着很强的对应关系,存在南、北2个强电场中心涡;(2)相对于发射站的位置,VLF电场中心点具有经度和纬度偏移,日侧地磁经度偏移均值大于夜侧,而地磁纬度偏移均值则小于夜侧;(3)日侧VLF电场强度呈现出周期性的年变化;(4)在VLF电场中心10°范围内,电场强度随距离快速衰减,衰减常数b在长达6年的时间内保持稳定.在以上研究结果基础上初步构建的卫星高度人工源电磁波空间分布特征,将为研究地表-电离层电磁波传播机理提供基础技术支撑.     

远场地震电磁辐射强度与孕震震级关系

基于垂直电偶极子激发源模型,首先研究了远场地震电磁场辐射场及其分布特征,其次分析了远场地震电磁辐射强度与孕震震级之间的关系.结果表明垂直电偶极子激发源可以解释孕震区激发电磁辐射现象,是激发地震电磁辐射最有可能的激发源之一;远场地震电磁辐射强度的对数与地震震级呈线性关系,直线的斜率与孕震区裂隙特性分布及其电磁特性有关.研究结果对进一步认识地震电磁辐射现象和拓宽地震监测预报思路均有积极意义.     

DC-induced acoustic emission in saturated sand models of sedimentary rock

The results of laboratory experimental studies of the DC-induced acoustic emission (AE) in saturated sand models of sedimentary rock are presented. It is shown that direct current acting on a geological medium generates acoustic vibrations in it. The experimental methodology is based on recording acoustic pulses generated by the rock model (sample) when the electric field is applied. The amplitude-frequency parameters of the AE signals depend on petrophysical properties of the solid phase, on the salinity of porous medium, and the electric field (current intensity and voltage). The above research is the first step towards the full identification of the characteristics of the AE signals generated by rocks in a DC electric field.     

Observations on the leader-return stroke of cloud-to-ground lightning with the broadband interferometer

Radio frequency observations of cloud-to-ground lightning (CG) were made in 1999 in Guangdong Province with the broadband lightning interferometer. In this paper, radiation source locations and electric field waveforms are analyzed for different types of breakdown events, including the preliminary breakdown of in-cloud activities, the stepped leaders of initial strokes to ground and activities during and following return strokes. It is shown that the structure and development of lightning discharges and associated breakdown processes can be reconstructed by using this new type of lightning radiation source location system. The detectable radiation of lightning was primarily produced by the negative breakdown process. The channel was concentrated with few branches during the preliminary breakdown stage of CG lightning flashes. The radiation sources appeared generally at the tip of the channel. During the late period of the stepped leader, the radiation sources were dispersed with branches extended away from the main channel. The radiation sources were in a certain length segment of the channel and the altitude of the segment descended along with the propagation of the leader to the ground. During the preliminary breakdown and the stepped leader of initial strokes to the ground, a sequence of fast negative streamers were observed to start continually from or farther away the lightning-initiated region and propagate along the developed leader channel, which may supply negative charge that assisted the leader’s development. The progression speed of fast negative streamers was about ten times faster than the average speed of lightning channel.     

Experimental study of ultralong wave band for electro－magnetic signals and acoustic emission during rock fracture

Ｅｘｐｅｒｉｍｅｎｔａｌ　ｓｔｕｄｙ　ｏｆ　ｕｌｔｒａｌｏｎｇ　ｗａｖｅ　ｂａｎｄ　ｆｏｒ　ｅｌｅｃｔｒｏ－ｍａｇｎｅｔｉｃ　ｓｉｇｎａｌｓ　ａｎｄ　ａｃｏｕｓｔｉｃ　ｅｍｉｓｓｉｏｎ　ｄｕｒｉｎｇ　ｒｏｃｋ　ｆｒａｃｔｕｒｅ（曹惠馨）（钱书清）（吕...