青藏高原东北隅弧形构造区现代中小地震密集区与历史强震的关系探讨

青藏高原东北隅地区位于青藏高原、鄂尔多斯和阿拉善三大块体交汇部位,发育一组以逆走滑活动为主的弧形断裂系,其新活动性强,历史及现代强震频发,是探讨现代中小地震密集区与历史强震关联性的理想地区,也是检验和发展小震密集区值方法及其适用条件的有利地区。本文采用甘肃省地震局对该区1970年以来1～5级地震仪器监测目录,利用网格点密集值方法进行计算分析,共划分出21个地震密集区。通过分析每个地震密集区内小震活动的时间分布特征及前人对历史地震和活动构造的研究结果,综合判断地震密集区与历史强震之间的对应关系,归纳总结不同震级历史强震密集区的持续时间,给出运用网格点密集值方法校核青藏高原东北隅历史地震的限定条件。研究结果表明:青藏高原东北隅弧形构造区大约66.7%的密集区对应历史强震,两者之间有较密切的关联性;且地震震级越大密集区持续时间越长,两者之间的拟合关系为:T=4.38×10~(-7)×M~(10.91)。

Discussion on the Relationship between Modern Medium-Small Earthquake-intensive Areas and Historical Strong Earthquakes in Arcuate Tectonic Region of the Northeastern Tibetan Plateau

Along the northeastern margin of the Tibetan Plateau, which is located at the intersection of the Tibetan Plateau, the Ordos, and the Alxa Block, a group of arc-shaped faults characterized by reverse strike-slip and strong new activity are developed. With frequent historical and modern strong earthquakes, the northeastern margin of the Tibetan Plateau is an ideal area for discussing the relationship between modern small earthquake-intensive areas and historical strong earthquakes. In this paper, based on the seismic instrument monitoring catalog of the study area since 1970, 21 earthquake intensive areas are divided by using the calculation method of density at grid nodes. Through the analysis of time distribution characteristics of small earthquake activities in each earthquake intensive area and previous research results of historical earthquakes and active faults, the corresponding relationship between earthquake intensive area and historical strong earthquake is comprehensively judged, and the duration of historical strong earthquake intensive area with different magnitudes are summarized. Meanwhile, this paper also presents the limited conditions for using the calculation method of density at grid nodes to check the historical earthquakes in the northeastern Tibetan Plateau. The results show that about 66.7% of the earthquake-intensive areas in the study area correspond to historical strong earthquakes, and there is a close correlation between them; The larger the magnitude of the earthquake, the longer the duration of the concentrated area. The fitting relationship between them is: T=4.38×10^-7×M^10.91.