基于震源机制解分析邢台地震的发震构造

Determination of the Xingtai earthquake seismogenic structure based on the focal mechanism solution

摘要:

活动断层几何形状的确定为评估一个地区的地震危险性提供重要的理论依据,邢台老震区内构造背景复杂,前人对邢台地震的发震构造展开大量研究,取得丰富成果。通过震源机制节面聚类得到邢台地震发震断层的走向、倾角及其标准差,综合前人研究结果求取发震断层面的平均解；结合区域地壳应力张量,估计该断层的滑动方向及其误差,分析该区域的地震活动危险性。结果表明:邢台地震发震断层的走向为32.45°,倾角为79.44°,滑动角-153.96°,标准差为4.55°。该断层为走向NNE、倾向NWW的高倾角走滑型断层,而非正断性质的新河断裂。区域地壳应力场在断层面上产生的相对剪应力为0.83,相对正应力为0.59。该断层不是最大剪应力的断层面形状,但剪应力强度仍较大,表明该断层在地震能量积累和释放过程中仍起到必不可少的作用。

Abstract:

The determination of the geometry of an active fault provides an important theoretical basis for assessing the seismic risk of a region. The structural background of the Xingtai earthquake zone is complicated. Many previous studies on the seismogenic structure of the Xingtai earthquake have been conducted, and plenty of results have been reported. In this paper, we evaluate the strike and dip angles of the seismogenic fault of the Xingtai earthquake as well as their standard deviation by clustering nodal planes of focal mechanisms. Then, the average solution of the seismogenic fault plane is obtained by synthesizing the previous results. Finally, using the crustal stress tensor in the region under investigation, we estimate the sliding direction and its standard deviation and analyze the seismic activity risk. The calculated values of the strike, dip, and rake angles of the seismogenic fault are 32.45°, 79.44°, and -153.96°, respectively, with a standard deviation of 4.55°. These values indicate that the fault under investigation is a high\|dip angle strike\|slip fault extending from NNE to NWW rather than a normal Xinhe fault. The estimated relative shear and normal stresses applied to the fault are 0.83 and 0.59, respectively. These values are based on the regional stress field. The shear stress applied to the fault is high, indicating that the fault is essential in the accumulation and release of seismic energy.