地震矩张量元素M_(rr)的空间分布与中国大陆岩石层地块

用哈佛CMT目录和中国地震震源机制目录给出了地震矩张量元素Mrr的符号的空间分布。这种空间分布图像相当于Tanimoto等 ( 2 0 0 0 )的“地壳势能变化”的空间分布图像的一种简化形式 ,Mrr的符号代表了地震震源处的应力状态。之所以进行这种简化是因为在相当多的情况下 ,地震的震源或矩心深度难以测准 ,并且震源机制目录的完整性得不到保证。将Mrr的分布图像与中国大陆岩石层地块的分布图像进行对照 ,可以发现由Mrr标志的地块内部的应力状态具有相当的一致性。地块边缘处的应力状态与地块内部的应力状态不同 ,似乎表明地块本身具有一定的整体性 ,同时地块之间存在相对运动

SEISMIC MOMENT TENSOR ELEMENT M_(rr) AS A SIMPLIFIED REPRESENTATION OF CRUSTAL POTENTIAL ENERGY CHANGE: ITS SPATIAL DISTRIBUTION PATTERN AND RELATION TO THE CONTINENTAL TECTONIC BLOCKS IN CHINA

Spatial distribution of the signs of the seismic moment tensor element M rr is mapped by using the Harvard CMT catalogue and the catalogue of earthquake focal mechanisms in China. This distribution pattern corresponds to a simplified version of the change of crustal potential energy calculated by Tanimoto and Okamoto (2000), in which the sign of M rr indicates the state of stress at the seismic source. When M rr is positive, it represents a compressional state; when M rr is negative, it represents a tensional state. We define the 'mixed state' for the case that positive and negative M rr are mixed together, which corresponds to a complex stress state with a significant shear component. This simplification is taken because for many earthquakes the focal depths cannot be precisely determined so that the calculation of crustal potential energy cannot get reliable results; moreover, for most of the regional/local catalogues of focal mechanisms, their completeness cannot be ensured. Comparison between the spatial distribution of M rr and the dynamic pattern of continental blocks in China shows that the stress state within each tectonic block has significant consistency, while the stress state at the boundary is different from that within the block, implying the existence of the blocks and their relative motions to each other.