21世纪全球三次M_W9.0左右地震的孕育过程研究

Investigation into the seismogenic process of three earthquakes with about MW9.0 in the globle in 21 century

系统分析了21世纪以来全球范围内发生的三次M_W9.0左右地震的孕育过程.验证了实际地震孕育过程与岩石力学实验揭示的应力积累过程和后续的临界状态(或亚失稳阶段)特征具有一致性.研究中利用视应力和b值分析构造应力动态变化,以描述地震活动与地球自转之间的相关性的统计检验参量P值评价震中及其附近地区地壳介质的临界状态.得到的结果显示,三次M_W9.0左右地震前震中及附近地区构造应力都表现出明显而连续的增加过程,持续6~10年左右.通过对应力增长期间震中附近较大区域内的b值下降幅度空间扫描,发现震前在破裂区及其附近存在一个b值下降幅度高值区,其相对下降幅度比其他地区都大,反映的是这个地区的应力增加幅度比其他地区都大.低P值(<5%)表示地震活动与地球自转之间的相关性显著,即,与地球自转相关的地震活动所在区域地壳介质处于临界状态.P值随时间变化表明,一般低P值在震前约4年内出现.在P值达到最低值期间,低P值(<2%)在空间上的分布与未来强震震中关联性较好.低P值区是极不稳定区,初始破裂一般在其内及附近发生,这是完全可以理解的.文中也给出了其他一些类似的震例结果.本研究所得结果不仅对利用岩石力学实验研究地震孕育过程,利用实验结果指导地震预测研究具有现实意义,同时对实际地震震情判定也具有重要意义.

In this article, the seismogenic process for three massive earthquakes (MW≈9.0) that occurred in the world in this century was systematically investigated. The increasing stress stage and the subsequent critical state revealed by the rock mechanics experiment were confirmed in the actual seismogenic process. In this analysis, the tectonic stress was detected by jointly using apparent stress and the b-value. Furthermore, the P-value, a statistical test parameter that depicts the correlation between seismicity and Earth's rotation, can be used to estimate the critical state that the stressed medium in and around the epicenter may approach. The obtained results are shown as follows: Before the three enormous earthquakes, the tectonic stress showed a continuous increasing process, lasting about 6~10 years. We mapped the spatial distribution of the relative changes in b value and found an area with higher relative decreases in b value in and around the rupture zone before the earthquake occurred, reflecting larger values of stress increase in this area. Lower P-values (< 5%) indicate a significant correlation between seismicity and the Earth's rotation namely, the related seismic area could reach a critical state. The analysis of P-value vs. time showed that lower P-values usually occurred within ~4 years before the occurrence of the mainshock. Lower P-values (< 2%) correlated well with the epicenter when the P-value reached the lowest. The area with lower P-values is extremely unstable, therefore the rupture initiates around it is reasonable. Similar results obtained from other case studies are also provided in this text. The findings of this study are highly significant for earthquake prediction in real-time as well as for the practical study of the seismogenic process by rock mechanics experiment and the guidance of earthquake prediction by experimental results.