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用分布在 8 km范围和主震前5 0 0小时内的前震时空图像 ,研究了 1 993～ 1 996年期间的 5次科依纳主震 (M 4.3～ 5 .4)的破裂成核过程。成核过程发生在两个阶段 ,即主震动态破裂前的准静态和准动态破裂过程。主震发生前 ,观测到成核区以 0 .5～ 1 0 cm/ s的速度扩展 ,直到其直径达到约 1 0 km为止。还发现破裂成核开始于浅部 (<1 km) ,然后逐渐向深部发展 ,在孕震层底部 (大约在 8～ 1 1 km深处 )引起主震。地震在浅部成核可归因于科依纳和瓦纳 (Warna)水库在亚静水压条件下引起的孔隙压力增加的结果 ,而破裂向孕震层底部的传播可能受沿断层带的局部应力集中和较深处的孔隙压力扩散的控制。
The time-space images of foreshocks distributed over a distance of 8 km and 500 h before the main shock have been used to study the nucleation and fracture processes of the five Main Generators (M 4.3-5.4) during the period from 1993 to 1996 . The nucleation process takes place in two stages, that is, the quasi-static and quasi-dynamic rupture before the main shock dynamic rupture. Before the occurrence of the main shock, the nucleation zone was observed to expand at a rate of 0.5-1.0 cm / s until its diameter reached about 10 km. It was also found that nucleation of fractures started in the shallow part (<1 km) and then gradually progressed to the deep part, causing the main shock to occur at the bottom of the seismogenic layer (about 8-1 1 km deep). The shallow nucleation of earthquakes can be attributed to the increased pore pressure induced by sub-hydrostatic conditions in the Kojuna and Warna reservoirs, and the propagation of fractures to the bottom of the seismogenic layer may be affected by Local stress concentration and deeper pore pressure diffusion control.