Abstract:This paper deals with the physical bases of eleven kinds of earthquake precursors.1.Seismic activity pattern;2.Source parameter of small earthquakes;3.The anomaly in seismic wave velocities;4.Change in electric resistivity;5.Gravity changer;6.Geomagnetic change;7.Measurement of crust stress by means of hydro-pressure fracture;8.Seismic prospect;9.Crust deformation;10.Underground water;11.Macro-phenomena.

Abstract:In solid physics, the image force is a force with which the free surface attracts the crack to wards itself. In reality the earth surface is a typical free surface. Besides, we regards the adjustmentary elements in combination model of source preparation, such as creep fault, plastic region, cracks region and the like, as free surfaces to some extent. According to the above-mentioned view point, we discuss some questions as follows:
1. When the creep slip just before earthquake in stress accumulation element is propagating and near to the free surface, and the free surface Will attract the creep slipping to wards itself.
2. When one of adjustmentary elements located at the end of earthguake source begins to extend, other adjustmentary elements will attract it promote its propagation.
3. When the appearance of some short-term and immediate precursors on the earth surface or adjustmentary elements is synchronized with the image force,it means that the-image force has already influenced the source and the earthguake will soon occur possibly.

Abstract:A set of P and S travel time tables from Chinese earthquakes was independently constructed in 1979. As for the effects of the new tables in practical experiments, this paper describes some tests on a number of earthquakes. Compared these tables with Jeffreys-Bullen tables and others, the practical experiences have shown that the new tables are relatively accurate and more applicable in the Chinese region in determining focal parameters than J-B tables.

Abstract:A number of earthquakes are associated with active faults. In the absence of measuring data, we intend to deduce which have faults are apt to be active. Based on the experimental and measured results, it is shown that direction and magnitude of external stress field as well as thickness and strength of faults are main factors which have affected the reactivation of faults.

Abstract:After the Tangshan earthquake(M_s=7.8, July 28, 1976) a series of earthquakes occured in the Ninghe region. It is called the Ninghe earthquake swarm. In the Ninghe earthquake swarm are found seven earthquakes whose waveforms are different from others in the region, but similar to each other. These earthquakes with similar waveforms are characterized significantly by the foreshock. Such earthquakes are regularly followed by moderate-strong earthquakes with magnitude Ms ≥ 5.5 about the same period in the Ninghe region. Based on the such foreshocks with similar the main waveforms, the main fracture plane in the Ninghe region has been investigated, and it may be the left-lateral nodal plane orientated NW.

Abstract:Based on the data of fourteen earthquakes mechanism solutions(M_s ≥ 3.5), the average orientation of principal compression stress axis (NE74°) and its dip (18°) in Xiji-Haiyuan-Guyuan region have been obtained. In connection with the data of crustal deformation measurements and the deep structure, the relations between tectonic stress field and seismicity have been discussed.

Abstract:In this paper, based on the theory of finite elastic deformation, we have obtained the stress components of the crust of the Earth under uniform angular velocity. After this, infinitesimal elastic deformation theory is appied to get the additional stress due to the change of angular velocity.

Abstract:This paper, based on the basic conclusions of the rupture mechanics, on a geological understanding of the rupture formation process as well as on some factual accounts of earthquakes,discusses the role of the stretching stress during the process of seismic rupture formation. It holds that an active,role is played by the stretching stress in the earthquake process.This serves as a necessary supplement to the present point of view that earthquakes result from shearing break.

Abstract:Does any relation between microtremors and ground motion induced by the earthquake exist? And what is the relation like? There are different answers by different researches. The Songpan earthquake in 1976 supplied, the chance to discuss this problem. From the investigation we come to the following conclusions:(1)Both the acceleration and the maximum amplitude of Fourier spectrum of ground surface motion induced dy earthquake increase with the earthquake magnitude increasing; and both the amplitude of microtremors and its Fourier spectra increase with the altitude of observation site and the thickness of alluvial stratum increasing. (2) The amplitude of microtremors and the surface motion induced by different series of earthquake in the same site appears to have certain direction. (3)The characteristics of the Fourier spectra of the same series of earthquake are exactly alike. (4)The old style wooden house of one storey does not affect the spectrum of microtremors, but the site condition obviously affects the Fourier spectrum of the microtremors of the wooden house.
By these analyses it is concluded that there is no obvious relation between spectra of ground microtremors and ground surface motion induced by the earthquake.

Abstract:In the recent studies of seismology and geology, satellite photographic analyses and drilling and geophysical prospection, the author has found that beneath the Guanzhong plain, there are some indications of extensively developed NNE structure. So far as this area is concerned, there are four structural zones with firstclass structural features. They should be the component parts of the Neocathaysian structural system of North China. It is a very active structural system at present, which reforms the antecedent structural plane, affects and controls the development of mophostructure and water system and controls the distribution of seismic actiyities and geothermal anomalous area. The small earthquake activities of this area correspond with the strong earthquake activities occurred in North China in recent years. They may be regarded as the indications of future strong earthquake in North China.

Abstract:In this paper, the favourable conditions of the earthquake activities in the Danjiangkou reservoir area, stress field since Hercynian period, characteristics of Seismicity, cause of its formation and its developing trend are discussed. Our tentative consideration is that, the occurrence of the earthquake activities is due to its different situations and different conditions, i. e. 1.It lies on the intersecting line of two groups of different structure, on the contact border of uplift and subsiding rift blocks and in the section of strong differential movement, which is the contact position of rock in different types; and 2. It occurs under special hydrogeological environment and the action of compressive stress in a direction of NEE and slips owing to its water permeating into two groups of shear surface. The major reason of the earthquake activities in the Danjiangkou reservoir area is its favourable geological conditions. The water in the reservoir gives rise to vertical and pore pressures is the secondary reason. As to the developing trend, the earthquake of Ms=4.7 occurring in November 29, 1973 may be the highest magnitude induced by a water level line to 157 meters high. An earthquake of Ms=5 will possibly occur when finishing the project in the second period. This point of view will be worth certain reference to fully utilize and bring into play the effect of the Danjiangkou reservoir and is favourable for constructing the project of the second period.

Abstract:在室内的岩石破裂实验中,曾多次观测到波速的各向异性。托切尔(D,Tocher)的结果表明,平行压力方向波速的增加比垂直压力方向快得多。在某些情形下,差别大约超过10%^[1]。1973年古普塔(I.N.Gupta)的实验认为P波速度下降的最大值发生在最小压力轴方向上^[2]。

Abstract:地电是地震前兆测量中一个重要的手段。在地震预报中起着一定的作用,受到国内外地震工作者的重视。但也存在着一些困难和问题。目前,国内外地震工作者(包括物探工作者)都在探索解决这些困难和问题的途径。

Abstract:我校有一口机井,1974年开始观测,每五日测一次。1976年7月28日唐山地震后改为每日测1-3次。该井处于贯穿天津市区的天津北断裂上。岩性以粘土质较多。反映了沼泽相的沉积特点。该井深216.88米。

Abstract:1906年12月23日北京时间2时21分在新疆玛纳斯西南发生的八级地震,历史资料虽有记载,但有关地面破坏的详细情况则无反映。自1972年以来,我局所属地质人员曾多次深入震区调查访问,已作了几个专门总结。