Abstract:In this paper, using the division of plate tectonics for reference, we have discussed that the Orduoce Block may be an independent block based on some facts of geology and seismology. And by the stress field from the solution of earthquake source mechanism and distribution of water-system etc. we have shown counterclockwise torsion in this block, which is used to discuss the regional seismicity. When comparing the movement of the block with the torsion of the cylinder of elliptic section, we found theoretical pattern of symmetric rise-sinking will show no difference from the pattern of tectonic motion of the block in Quaternary period. We have analysed symmetric echo of seismic activity of block boundary, mechanical character of the area of occurring great earthquake, the distribution of great earthquake along block boundary, the collusion of boundary fault from the earthquake and mechanical preperties of the fault etc. by the result obtained from the study of cylinder torsion of elliptic section. On this basis, we put forward five respects which are needful to estimate the trend of earthquake of block region. Then, shortrange trend is estimated.
After the preliminary analysis of force source we consider that Pacific plate play a main part in the movement of the Orduoce block, but the reflection of Indian Ocean plate can't overlooked too in it.

Abstract:This paper includes three parts. At first, some characteristics of tide of underground water have generally been introduced; then, the relation between tide of underground water and earthquake caused by pumping water and the mechanism of induced earthquake have been proved from space-time behavior; finally, the three existing problems in the investigation on tide of underground water have been discussed.

Abstract:The main parameters and microscopic phenomena of the four particular earthquakes occurred in the area of the Sanxia area have been introduced in this paper. These earthquakes seem to have two macroscopic epicenters of which the cause of the formation must be much complicated. The area of the Three Gorges is located in the gravity gradient zone in the east of China and the Moho here is rather declivitous. Thus, the single abnormal region of seismic intensity at a distance from the epicenters may occur because seismic reflection waves are focused and reflected by the Moho discontinuity.

Abstract:Since 1976, by using the non-damping horizontal pendulum tiltmeter at the range of 1.7"-5" period. we have recorded one wave anomaly signal before a series of strong earthquakes respectively. And by means of it we Predicted some strong earthquakes, such as Song pan earth quake (8.16.1976, Ms=7.2) and Yanyuan earthquake (11.7.1976, Ms=6.9). The practice of seismic prediction has proved that the wave anomaly is a possible earthquake precursor.
This paper is a conclusion of our detection during 1976-1982, and a preliminary discussion on the genetic mechanism of the wave anomaly.

Abstract:In this paper the aftershock activity of shallow strong shocks(M≥5) in China continent is analysed, it shows that the duration of aftershock sequence has some regularity. There are four periods of aftershock activity which consist of initial stage, middle stage, late stage and extremely late stage.
According to certain characteristic of seismic activity of the north China, we suggest some estimated method of strong aftershocks and late strong aftershocks. Some corresponding relation exists between the adscissa intercept in b value of the earthquake sequence and the maxium magnitude of aftershock as well as between the divergeney point of b value curve and the frequency of the strong aftershocks. The possible places of strong aftershocks are the extend rupture direction of strong earthquake, the seismic gap in aftershock sequence and the edge of the aftershock region. However, there are some corresponding relations between frequency change of earthquake sequence in aftershock region and the duration of strong aftershocks.
In this paper mechanism of strong aftershocks is discussed in theory. The strong aftershocks of initial and middle stage associate with the surplus strain energy and the stress distribution in seismic region. The late and extremely late strong aftershocks associate with the region stress increased and its propagating process in seismic zone.

Abstract:In this paper, we recollected all data of the M≥7(1)/(2) earthquakes occurred in China during the years 7 B.C.-1976. The new catalogue of earthquakes have new improvement mainly in the region of west China. we discovered two predominant distributions, before or after each earthquake (M≥8) and another earthquake(M≥7.5). There's hardly any difference between the work of professor Xu Shaoxie et al. and the two predominant distributions, one at a shorter distance of 500-600km, the other at a longer distance of 1150-1300km. In addition, we found that the dispersion would be best if less than 30 years of time difference between two earthquakes, We also found the similar result of strong earthquakes occurred in U.S.A.

Abstract:Applying Changli, Baodi, and Beijing geomagnetic vertical component data, the correlitivity with Hongshan was described. The results show that at all of three stations occurred abnormal variation before Tangshan earthquake. Abnormal variation at Changli was the most obvious, abnormal period lasted for a couple of months, abnormal amplitud was about-10 nt. Based on the results of the references(1,2) and this paper, the mechanism of the geomagnetic abnormal variations was discussed. The process, preseismic instability of inclusion-porous fluid diffusion-dilatation and hardening of inclusion, probably was the reason for the above geomagnetic abnormal variation.

Abstract:In this paper, the reflection and refraction phases of the earth crust and uppermost mantle in Jiangsu-Zhejiang region are proved by using the explosive data of this region recorded by some seismic stations in Jiangsu, Zhejiang, Anhui provinces etc. And its main earth crustal structure has been obtained by the generalized linear inversion method.
Finally, the results indicated that this region is multi-layer crustal structvre and its average thickness about 33km.

Abstract:The linear fractures so called by this paper are a series of images of straight lines on the LANDSAT's photoes, and most of them are caused by tectonic activities, such as fault-controlled river systems, offset streams and ridges, subsidence lake basins and grabens, deviational alluvial fans, straight seashore lines and somemicrofractures which may result from the recent crustal movement. Therefore, the word "fracture" can not be limited to geological faults.
We inlay and interpret 123 photoes from LANDSAT-1, 2, 3, in the region between E 104°-122°and N 34°-41°, which covered 1.36 million km². The photoes used by us are coarse and black-white, so there are errors of 6-7mm in our inlay. The density slicing had been done in part of the typical photoes. In order to check our interpretation, some field examinations have been carried out. We discover that the activities of all kinds of the fractures in the latest geological time were shown into two aspects:
1. Continuity. Most of the fractures activities occur along the old faults of pre-mesozoic era.
2. Originality. Part of the fractures originated in the Neogene period, especially in the Quarternary era.
All the characteristics as mentioned above are eyecatching on LANDSAT photo images.
In the course of our analysis, we find that in the whole region of North China, various typies of fractures are shear, particularly in recent tectonic stress field. In spite of their criss-cross each other, they are in order and fall into three groups of conjugate systems, e. g. EW/NS, NNE/NW-NWW, NNW/NE-NEE. Finally, the authors have tried to find out the relationship between the seismicity and the linear fractures.

Abstract:Model DSL-1 Portable Seismograph is a system of microseismic detection designed for various purposes by which the natural earthquakes, man-made explosions, ground-micro-tremors and other engineering vibrations here been recorded in the recent years.
In order to interpret quantitatively seismograms, We have deduced the analytic expressions of dynamic response of the system, and calibrated its frequency-response characteristics as well. It is shown from the given expressions that the computed curves of dynamic characteristics are consistent with the results of calibration.

Abstract:In the time near to earthquake occurrence, a source region and its neighbor region are in unstable state. In this case, some weak external factors, such as tidal forces, atmospheric pressure or magnetic storms, may modulate the processes in these regions and the precursors produced by these processes. If we find some precursors synchronized with some external factors, we should pay a special attention to possibility of earthquake occurrence. In previous paper, we stated many of examples of our country to demonstrate the modulation model. In this paper, we present some examples quoted from foreign countries to demonstrate the model. It should be pointed out that the external factors may possibly cause, aseismic slip and false precursors.

Abstract:In this paper the variation of anomalous amplitude of seismic wave observed before stronger earthquakes and the results of simulated experiment and theoretical analyses have been closely combined and a comparison between them has been made. With the aid of variation of crustal medium, the explanation of the premonitory anomalous characteristics of amplitude ratio have been given. Since the variation of medium reflects that of tectonic stress, the physical explanation may possess the view of cause of formation.