It can be concluded: 1) isolated earthquake features simple earthquake dislocation mode, high or very high stress drop, low or very low apparent stress and low heterogeneous level of medium in earthquake source region;

2) multiple earthquake (strike-slip) features complex earthquake dislocation mode, low or very low stress drop, high or very high apparent stress and high heterogeneous level of medium in earthquake source region.

6. Revealment of differences of deformation field of earthquake source region and its vicinity, and variations of pattern dynamic parameters of crustal deformation field by application of pattern dynamic method.

Based on the concept of information field of earthquake precursors, using the method of the spatial linearity to calculate the geomagnetism data of Z direction we can find the precursory characteristic value-spatial linearity short-term abnormal characteristic value (α), which describes the earthquake source region in the process of earthquake preparation.

The results indicate that the value of tectonic ambient shear stress and apparent stress not only reflects strong or weak stress background in earthquake source region but also the information of stress background around earthquake generating area in special tectonic position,namely the small earthquake in seismic window of "seismic activity point" farther from the future strong earthquake epicenter. The difference of the stress state is distinct before and after moderately strong earthquake in East China region.

This low-frequency earthquake source region, in which no high-frequency events occurred, may be the steam zone within the actual vent of Ruapehu Volcano.

Therigidity describes how hard it is to bendthe rocks in the earthquake source region with a shearing motion.

It is further observed that in all the sections the velocity variation shows almost a layered structure, away from the earthquake source region.

The numerical theory of the three-dimensional electromagnetic induction is a powerful tool in studying the seismo-magnetic induction effect, as well as the lateral inhomogeneity of the electrical structure in the earth's crust and upper mantle. The complete numerical equations were established in our preceding paper[1]. In this paper we first show both theoretically and numerically the uniqueness, convergency and stability of the solution of these equations under definite conditions. Secondly, some model calculations...

The numerical theory of the three-dimensional electromagnetic induction is a powerful tool in studying the seismo-magnetic induction effect, as well as the lateral inhomogeneity of the electrical structure in the earth's crust and upper mantle. The complete numerical equations were established in our preceding paper[1]. In this paper we first show both theoretically and numerically the uniqueness, convergency and stability of the solution of these equations under definite conditions. Secondly, some model calculations are carried out for various periods of source field and burying depths of local anomalous bodies to study the space-distribution and frequency characteristics of the seismomagnetic induction effect. Under the assumptions that the dimension of the anomalous body corresponds approximately to the source dimension of an earthquake of magnitude 5-7, and that its conductivity is ten times as large as the normal value, the results for source period of a few seconds to a few minutes show that the largest anomaly, relative variation about 30%, of the horizontal component takes place in the central part above the anomalous body, and that the largest anomaly, relative variation 50%, of the vertical component takes place at the two sides perpendicular to the direction of the source field. Therefore, observing the anomalies of short period variations of the field might be a promising approach to monitoring conductivity variations associated with earthquake process. The anomalous intensity of the seismo-magnetic effect, however, decreases quite rapidly with distance, so that the observing sites have to be near the earthquake source region; and this brings about the difficulty for their arrangement in advance.

After the Tangshan Earthquake of 1976, strain adjustment took place in the earthquake source region by the occurrence of a series of aftershocks. The relative strain changes in the earthquake source region may be calculated from the energies of the aftershocks by the Benioff's formula. On the whole, these changes are consistent with those obtained from the vertical deformation observed at a geodetic levelling point within the earthquake region. The correlation between the variations of...

After the Tangshan Earthquake of 1976, strain adjustment took place in the earthquake source region by the occurrence of a series of aftershocks. The relative strain changes in the earthquake source region may be calculated from the energies of the aftershocks by the Benioff's formula. On the whole, these changes are consistent with those obtained from the vertical deformation observed at a geodetic levelling point within the earthquake region. The correlation between the variations of the radon content in water and the changes of relative strain is rather good. Further discussion based on such observations suggests that the increase in radon content in water after the main shock may be related to the strain adjustment in the earthquake source region and the cumulative increase of macroscopic fractures of the water bearing rock formations.

In recent years, in the region around the cities of Beijing and Tianjin, work of seismic deep sounding has been carried out. The purpose is principally for studying the structure of the crust and upper mantle which involves the earthquake source regions of this seismically active portion of the North China Plain. By observing wide angle reflected waves, the reflection PM from the Mohorovicic Discontinuity and PM from the intermediate layer within the crust are recorded. Eefracted waves from the Mohorovicic...

In recent years, in the region around the cities of Beijing and Tianjin, work of seismic deep sounding has been carried out. The purpose is principally for studying the structure of the crust and upper mantle which involves the earthquake source regions of this seismically active portion of the North China Plain. By observing wide angle reflected waves, the reflection PM from the Mohorovicic Discontinuity and PM from the intermediate layer within the crust are recorded. Eefracted waves from the Mohorovicic Discontinuity have been observed. Assuming a horizontally homogeneous layered structural model, computations of the velocity structure by the damped least square method of inversion were done. Eesults show that apparently, in this entire region velocity varies with depth, as a layered earth. On the other hand, horizontal inhomogenuity actually exists.