Abstract:The statistical method of power spectral analysis has been used to analyze three indexes of (1897-1977)global seismicity:annual seismic energy release(ΣE), annual number of large earthquakes(ΣN)and annual mean of large earthquake magnitude(M). Then, the finite impulse response(FIR) method is applied to construct the desired filter (F1, F2, F3, F4, F5, F6).
The power spectrum of ΣE and ΣN represents five peaks:8, 6.7, 4.4, 3.6, and 2.0years(Fig. 1), their cross-spectra and coherence coefficients are shown in Fig.2.The variation of ΣE after filtering may approximately be the inverse propertion to the long-term changes of sun-spot activities. The power spectrum of 6.7, 3.6, and 2.9 years of ΣN and ΣE is very similar to those of earth rotation(6.9, 3.7, and 2.9 years). In brief, it is suggested that the general tendency of global seismicity during the 1897-1977 period may be closely related to sun-spot activities and the earth rotation.

Abstract:In this paper we investigate the method of finding seismic gap and determining earthquake preparation area and discuss the physical mechanism of forming big seismic gap from dynamic view point.
1. Determination of earthquake preparation area
The occurrence of a great earthquake has a dynamic action on the neighbouring crustal medium. This action is different for various media with different strength. In the regions with low rock strength, moderate or small earthquakes occur, but seismicity is low in the regions with high strength. Therefore we regard the dynamic effect of great earthquake occurrence as a detective measure for finding the seismic gap and deciding the earthquake preparing region located in some distance from the former earth-quake. According to the above-mentioned method and the combination model of source formation (i. e. the earthquake source consists of the stress accumulating element and two stress adjustment elements located at both ends of the stress accumulating element), we ha used the dynamic detective effect to check the seismic gap and the earthquake preparing region of four great earthquakes located in sourth western China. The estimated intensities are nearly the same as the actual earthquake intensities.
2. Physical mechanism of the formation of big seismic gap
In general, there are two kinds of seismic gap. The first is a smaller gap with its areas approaching the dimension of the source volume. Such gaps can be explained with the combination model. The second is a big gap with its dimension much bigger than that of the source volume. A new explanation for the formation of big gap is proposed. A big gap may be formed when the vertical movement of the upper manlet acts on the overlaying crust in a very big area, in which the preparing source is involved. As the vertical movement can affect the medium strength and stress distribution, the gap, as mentioned in the combination model, will be enlarged. In this paper physical discussion and theoretical calculation for the formation of the big gap are given.

Abstract:This paper discusses the historical large earthquake reappearance pattern in its focal reigon of China. It has been Found that a number of the historical large earthquakel reappearances were distributed on the active tectonic zone in the western geosyncline of China. Most of the spatial locations earthquake in the focal region are repeated within the intensity Ⅷ area on the stretch reorientation of a main repture plane where the historical largest earthquake occurred. The empirical relationship between the magnitude of such earthquake reappearance in the magistoseismic area and the magnitude of the historical large shock is rectilinear as shown by the formulas (1) in the text. These can be used to determine the magnitude of the reappearance earthquake occurred in the magisto-seismic area.
Most of the interval reappeared earthquakes are within……100 years. The relationship between the earthquake reappearance time and the regional active tectonic dimension and extent:is as follows the larger and more intensive the active tectonic dimension is the longer the interval reappeared historical large earthquake in the magistoseimic area will be.
At last the characteristics mentioned above are physically explained and give a supplementary explanation of how to make use of them.

Abstract:In this paper the function of four-phase method to amplify the anomaly of seismic velocities ratio is discussed in greater detail than usual method. It reveals that this method is worth researching further and being proved by more seismic examples.

Abstract:Based on the strain energy density theory on the unstable growth of mixed mode cracks, this paper discusses some problems on fracture law and activity characteristics of strong aftershocks occured at the end of main fracture of large earthquakes. Combining some relative examples, it suggested: 1. the angle between fracture planes of this strong aftershock and its main earthquake should be much more than zero degree; 2. this strong aftershock should generally locate at the corner of attenuation curve of aftershock frequence; 3. the relationship between fracture length and magnitude of strong earthquakes is quite close to the result obtained by Guo Zeng-jian and others. 4. the growth length is about 0.16 time that of main fracture.

Abstract:The Dengjiaqiao reservoir is located in Yidu county of Hubei province, and produces a storage capacity of about 4X10⁵M³. since June 1980 rainstorms continuously taken place in the west part of Hubei province. Reservoir was first fully impounded on 31 July of 1980, thus earthquake (M_L=1.9) was induced the next day.
Secimicity of the Dengjiaqiao reservoir is an event of tectonic-earthquakes type, Due to stormily increasing of rainfall and ground water flowing into underground streams, and permeating into fractures, and so pore pressure increased in some faults, and effective normal stress was decreased, In addition, full impounded lodging also made normal stress increase about 1 bar. This resulted in forming a fracture slip of the fault in NE direction.

Abstract:At present, the sudden change of radon content in ground water is regarded as a better index of immediately prior to the occurrence of earthquake. In this paper, our discussion will centre on the interferences presented in the sudden change of radon and their causes.
Based on the experimental results obtained from the field test station of radon measurement, we point out that many factors, such as methorological (rainfall), geological (landslip), hydrogeological (change of the hydrokinetical condition), environment of spring site(outcrop condition) and other accidental factors can lead to the mutation of radon content. For this reason we must take suitable measures to learn springs(wells) conditions so as to carry out the observation. only when the interferences are removed the precusor anomalies become may outstanding.
In this paper, we have also made discussion on the methods of distinguishing and eliminating the interferences. It is fully proved that to set up the hydrochemical station in the tectomic region and carry out comprehensive hydrochemical observation and research (including rodon dissolved gas and other chemical components)at more stations is an effectual way to identify interferences and define out the way forward for developing earthquake prediction by hydrochemical method.

Abstract:The effects of the sampling and the interpolation of strong motion data on the corrected accelerograms and integrated displacements are investigated in both frequency and time domains, It is found that the sampling of a record can be consideied as a low-pass filter which eliminates the high frequency contents in the record, but the interpolation of data does play a role of high frequency noise source which introduces high frequency noise into digital records. In is also founa that an unequally spaced sampling model will give a more accurate information than an equally spaced sampling model at the same sampling rate. But the latter will result in a wider range of flat frequency response than the former, than the former would. In comparison with the results given by the linear interpolation method, the parabolic one can generally provide with much better results, especially when a lower sampling rate is used.

Abstract:Since 1976 the ground fissures both in the city and suburbs of Xian have been strongly,developed and a lot of buildings located near by them damaged. For the last years these fissures Have brought to the attentions of many scientists and architectural departments,who have done much work and a number of papers dealing with the ground lissures have been publisted.

Abstract:The finite element method for analysing the effects of irregular topography on earthquake ground motion is presented in this paper. The emphases is laid on the discussion about the differences of the effects of irregular topography induced by the different soil conditions. The computer program also dealt with here.

Abstract:In this paper the cuthors introduce several formulae for interpolating the interrupted observation data in gravity station on the basis of the coordinates combinations theory, the authors also check the calculation dccuracy reached possibly, of these formulae by applying the practical observation data and indicate some principal problems which must be considered when we apply above formulae.

Abstract:In this paper the earthquake parameters of Ms≥4(3)/(4) during 1914 to 1965 in China have been revised using electionic computer. The applied method and results have been introduced simply. The results show that the accuracy of revised parameters(o.λ.φ.h)are all improved obviously.

Abstract:Based on the characteristics of hearing of catfish and their active habitude at night, we studied and made an automatic observation system with ultrasonic wave for recording activities of catfish prior to earthquakes. Observable results show that this system not only can sensitively record activities of catfish, but also has no effect on their normal activities, and surrounding sounds has no disturbance on it. At the same time, it can be applied to automatic observation of activities of other animals in water.
Preliminary observation data show that automatic recording activities of catfish presented an outstanding rinse in 48 hours before two strong aftershocks(M_L5.2 and M_L5.5) occurring in Tangshan region during our observation from Jan. to June. 1982.

Abstract:On the basis of observational data obtained in Gansu Province and its neighbour region, the district features of seismic velocity anomalies were investigated briefly. The results obtained may be useful for researches on the earthquake prediction in a given concrete seismically active region.