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在地震周期中,应力场的局部旋转也许可以作为表征各个断层段物理性质的一个指标。本文我们主要研究1999年土耳其西北部伊兹米特MW7.4地震的震前、两个月的余震期和震后阶段。使用震源机制数据的汇编资料,我们研究了应力场取向的时空变化特征,发现沿各个断层段存在明显变化。尽管伊兹米特主震前及其后两个月的余震序列反映出稳定的走滑状态,然而在阿克亚泽盆地之下余震期的早期主要为东西向扩张。在两个月的余震期中,我们发现主震期间有从走滑性质转换到正断层作用的明显变化,之后发生系统的回转,回到主震前的应力状态。这一应力回转首先开始于阿克亚泽盆地,产生了≤3m的同震滑动缺失,然后向东传播到87天后发生迪兹杰MW7.1地震的卡拉代雷和迪兹杰断层。我们的研究结果证实,地震周期中的应力场旋转时空变化是地震构造背景变化的一个有用指标。
During the earthquake cycle, the local rotation of the stress field may be used as an indicator of the physical properties of each fault segment. In this paper, we mainly study the aftershock and post-earthquake phases of the Izmit MW7.4 earthquake in northwestern Turkey in 1999, two months before and after the earthquake. Using the compilation data of focal mechanism data, we study the spatiotemporal variation of stress field orientation and find that there are significant changes along each fault segment. Although the aftershock sequence before and after Izmit’s mainshock reflected a stable strike-slip state, the early Aftershock periods under the Akhzentan basin were dominated by east-west expansion. During the two-month aftershock period, we found significant changes from strike-slip properties to normal faulting during the main shock, followed by a systematic turn back to the stress state before the mainshock. This stress swing first began in the Akoya basin, producing a coseismic slip of ≤3 m and then propagated eastward to 87 days after the occurrence of the Caladere and Dizije faults of the Dzięch MW 7.1 earthquake. Our results confirm that the spatiotemporal variation of the stress field rotation in the seismic cycle is a useful indicator of the change in the tectonic setting.