中国大陆微破裂过程和应力图案的变化

本文通过对我国大陆东经97°以东地区,1972—1978年发生的17,000多次M≥2.0地震的活动率(d值)和震级-频度关系(b值)的时空扫描,研究了我国大陆的微破裂过程及其与大地震的关系,并认为区域性的b值扫描图在很大程度上反映了区域应力图案的变化

ON THE MICROFRACTURE PROCESS AND CHANGES OF THE STRESS PATTERN IN THE CHINA CONTINENT

when studing time-space scanning of the seismic frequency ratio ( d value) and of the frequency-magnitude relation (b value) for about 17, ooo M≥2.0 shocks occurring in the China continent east of longitude 97?E during 1972-1978, we obtained the mic-rofracture process of continent crust and changes of following stress pattern; a set of inclined-conjugated and instable shear network at an interval of 5° probably formed within the crust with the effect of the bulk earth revolving, with the increase of regional stresses, average stress of the crust and mumber of times for appearing microfracture in the whole region, the area of microfracture expanded progressively along the instable shear network to made the network grow complete. The order of b value for an area of concentrating stresses is directly concerned in both the velocity of spreading microfracture and the increased area in seismic activity. The result is basically consistent with the Scholz's (1968).After occurrence of major earthquake, the area of growing microfracture was decreasing and coming back to a more uniform network with the decrease of the average stress on the whole region. The regional distribution of b values is related with the microfracture process in the whole continent of China. In addition, the experiment shows that b values is a function of the applied stresses and the regional change in the values may represent changes of the stress state and the scanning map of the b values can give to a great extent the stress patterns to the region