断层失稳前的扩展及电阻率前兆

本文根据断裂力学,研究了体应变e的特征,导出了传播范围的近似公式;探讨了与应变有关的地震前兆的一般规律,以唐山地震电阻率前兆为实例检验了上述结果,并由电阻率前兆初步反演了相应的震源过程及某些震源参数。     

THEORETICAL PROBLEMS OF DISCRETE GAUSSIAN ANALYSIS OF GEOMAGNETIC FIELD

Starting from the fact that Gaussian (spherical harmonic) analysis of geomagnetic field is a 'three-dimensional problem', some theoretical problems of Gaussian analysis arising from the discretization observational points are studied in this paper. Firstly, the orthogonality of discrete harmonic functions is discussed. Secondly, the basic relationship for estimating the errors of Gaussian coefficients to be determined in Gaussian analysis of discrete observational points is obtained by using perturbation method, and from this relationship the various factors influencing the errors of Gaussian coefficients to be determined and their relationship are studied. Finally, the investigation of the independence of Gaussian coefficients in discrete Gaussian analysis points out that if the distribution of observational points and the choice of weights make the orthogonality relations not satisfied, 'three-dimensional significance' of Gaussian analysis will be impaired.     

RESISTIVITY PRECURSORS AND SPREADING OF FAULT PRIOR TO ITS INSTABILITY

Based on fracture mechanics it has been found that earthquake precursors related to volumetric strain e are characterized by quadrants, blind zone and uneven propagation, and the approximate formulae for spreading range of precursor have been obtained. These results are coincident with the information of resistivity ρ_x observed before the Tangshan earthquake, and then mechanical explanations have been made for some precursors of ρ_x, such as precursors appearing concentratedly within the period of 1—2 years before the instability of the fault (i.e. subcritical period in which the fault spreads acceleratingly). Before instability of the spreading of fault, the range of e=10~(-6) reaches about 150 km, its propagating velocity is about 100 km/yr, the amplification coefficient of ρ_x is about 10~4, etc. The half length of fault before instability is about 35km. It seems that in propagating process the spreading of the fault is delayed by barrier.     

ANOMALIES OF SHORT-PERIOD GEOMAGNETIC VARIATIONS AND DISTRlBUTION OF HIGH CONDUCTIVITY LAYER IN THE BOHAI SEA AREA

In this paper, analyses of short-period geomagnetic events such as sudden commencementand geomagnetic bay, together with some quiet day, disturbed day and geoinagnetic stormvariations, recorded at 25 repeat stations in the Bohai Sea area during the years 1973--1979are presented. It is found that there are anomalies of short-period variations in this areaincluding the Tangshan earthquake region, and that local anomalies with periods rangingfrom 5 minutes to 2 hours along the Changli- Tangshan-Ninghe-Baodi belt (positive △Z ) andat Yantai (negative △Z) are most obvious. By applying the numerical theory of three-dimensional electromagnetic induction, an attempt is made to fit these anomalies to the struc-ture of high electrical conductivity in the upper mantle. The result brings to light an upliftof high conductivity layer, at the northern margin of which the Tangshan earthquake islocated. The additional thermal stress due to such an uplift calculated to amount to a thou-sand of bars may be an important possible source of generating force for the Tangshan earth-quake.     

渤海地区地磁短周期变化异常、上地幔高导层的分布及其与唐山地震的关系

本文分析了渤海周围25个地磁台站1973—1979年急始、湾扰等短周期事件,以及静日、抗日和磁暴的频谱成分,发现包括唐山震区在内的渤海地区存在地磁短周期变化异常。北部的昌黎、宁河、宝坻一带异常最强,垂直分量的变化△Z为正,南部的烟台附近异常最强,△Z为负,周期为5分钟至2小时的异常变化最为明显。应用三维电磁感应的数值理论,拟合了与这种短周期地磁异常变化相应的上地幔高导层电性结构,发现渤海地区有一上地幔高导层的局部隆起,唐山地震位于隆起部位的北侧边缘。与隆起构造相应的附加热应力,其量级高达千巴,很可能是唐山地震的重要动力来源。     

地球磁场的离散高斯分析理论

本文从地磁场的高斯(球谐)分析是“三维问题”出发,研究了高斯分析由于测点离散化而产生的一系列理论问题。包括:1.离散球谐函数的正交性;2.高斯分析在测点离散条件下的误差分析,给出了估计高斯系数误差的基本关系式,并由此分析了影响待求高斯系数误差的各种因素;3.测点离散条件下高斯系数的独立性,指出测点的分布和权重选取不满足离散球谐函数正交关系将影响高斯分析的“三维意义”。