The average seismic apparent stress and its distribution in Chinese mainland are presented by use of data of medium-strong earthquake from 1900 to 2005.

Based on different types of data of these events including earthquake sequences, stress drop and seismic moment, we discussed the intensity of apparent stresses of different earthquakes classified into two classes according to earthquake fault characteristics and earthquake types.

The authors calculate the apparent stresses of several strong earthquakes, relate the intensity of apparent stresses of the strong earthquakes with the magnitude of the successive earthquakes following the strong earthquakes to seek for the relationship between them, and point out the possibility of applying apparent stresses to seismic tendency prediction after strong earthquakes.

Seismic porosity and seismic stress of rocks can be inverted with seismic and geological data based on the theory of two phase medium.

The paper suggested that the generation of seismic stress is accompanied by the formation of “biaxial strain structure”.

In this paper, according to the data on the middle and strong earthquakes in China, we have preliminarily studied the relation between the characteristic of space time evolution of the seismic apparent strain field and the regions of 31 macroseism events since 1955.

The study results show that the orientation of compressive principal stress is NE and the modern tectonic stress field is in keeping with neotectonic stress field and seismic stress field.