从断层中心论向块体中心论转变--论活动块体在地震活动中的作用

讨论活动块体在地震活动中的作用。板缘地震在空间上呈线性分布，而中国大陆地震在空间上呈片状分布。大陆强震往往涉及两个以上方向断层的活动，且强震往往沿块体边界迁移或在其两侧断层上对迁。一些强震前后由中小地震震源机制解反映的Ｐ轴方向往往发生近９０°的转向，这种现象难以用区域应力方向变化来解释，但可从块体活动角度出发，用块体两个边界断层的先后错动来解释。地震前异常的远程效应、震后烈度异常分布图像以及地震序列特点等也显示了活动块体的作用。不同地区由地震活动性推测的块体活动方式有所差别，其原因可能和区域主压应力轴与块体两个边界断层走向的夹角不同有关。据此认为，在分析中国地震活动时要把视角从以活动断层为中心转变为以活动块体为中心

Changing viewpoint from fault to block-a discussion about the role of active block in seismicity

The role of active block in seismicity is discussed in this paper. Intraplate earthquakes almost distribute along a line in space generally, while the intraplate earthquakes in China scatter in a large region. Faults with more than two directions are often involved in a strong intraplate earthquake, and strong earthquakes usually migrate along one margin fault of a block or jump across the block. The P axis of focal mechanism of medium and small earthquakes often rotates about 90° around some strong earthquakes. This phenomenon is difficult to be explained by using the change of orientation in regional stress, but it can be explained by the alternate slip along two margin faults of a block. No matter what the long distant effects of earthquake on anomalies, the unusual distribution of earthquake intensity as well as the characteristics of earthquake sequences may also indicate the role played by active block. The movement mode of block inferred by seismicity may vary from each other in different region, which may be caused by the angle difference between the stress axis and the striking direction of two faults. Based on the facts mentioned above, it is suggested that the viewpoint should be changed from active fault to active block when analyzing the seismicity in China.