杨晨艺,石富强,季灵运,杨宜海,苏利娜,杨敏,郑怡. 2024. 2013年岷县漳县MS6.6地震和2017年九寨沟MS7.0地震震前地球物理观测异常空间分布机理分析. 地震学报,46(2):307−326. doi: 10.11939/jass.20230118
引用本文: 杨晨艺,石富强,季灵运,杨宜海,苏利娜,杨敏,郑怡. 2024. 2013年岷县漳县MS6.6地震和2017年九寨沟MS7.0地震震前地球物理观测异常空间分布机理分析. 地震学报,46(2):307−326. doi: 10.11939/jass.20230118
Yang C Y,Shi F Q,Ji L Y,Yang Y H,Su L N,Yang M,Zheng Y. 2024. Mechanism analysis of spatial distribution of the geophysical observation anomalies before the 2013 Minxian-Zhangxian MS6.6 earthquake and the 2017 Jiuzhaigou MS7.0 earthquake. Acta Seismologica Sinica46(2):307−326. doi: 10.11939/jass.20230118
Citation: Yang C Y,Shi F Q,Ji L Y,Yang Y H,Su L N,Yang M,Zheng Y. 2024. Mechanism analysis of spatial distribution of the geophysical observation anomalies before the 2013 Minxian-Zhangxian MS6.6 earthquake and the 2017 Jiuzhaigou MS7.0 earthquake. Acta Seismologica Sinica46(2):307−326. doi: 10.11939/jass.20230118

2013年岷县漳县MS6.6地震和2017年九寨沟MS7.0地震震前地球物理观测异常空间分布机理分析

Mechanism analysis of spatial distribution of the geophysical observation anomalies before the 2013 Minxian-Zhangxian MS6.6 earthquake and the 2017 Jiuzhaigou MS7.0 earthquake

  • 摘要: 对甘东南地区2013年岷县漳县MS6.6地震和2017年九寨沟MS7.0地震震前地球物理观测异常特征进行总结梳理。根据活动构造单元对地球物理观测台站进行区域划分,统计了相关构造单元上异常的数量和百分比,以及不同学科震前异常数量、百分比、异常持续时间等特征,并对异常的空间分布和机理进行分析,讨论了活动构造对异常分布的影响、异常强度与震源机制及断层应力之间的关系。结果表明:① 2013年岷县漳县MS6.6地震比2017年九寨沟MS7.0地震震前地球物理观测异常百分比高,两次地震的震前电磁异常和跨断层水准测量异常均较为显著,而流体异常不明显;② 震前地球物理观测异常分布与活动构造相关,2013年岷县漳县MS6.6地震震前异常主要集中在东昆仑—西秦岭断裂带和六盘山—海原断裂带,2017年九寨沟MS7.0地震震前异常则主要集中在龙门山断裂带和东昆仑—西秦岭断裂带;③ 两次地震震前地球物理观测异常分布均与GNSS速度场分布特征有较好的对应关系;④ 安德森断层应力模式解释了2013年岷县漳县MS6.6地震(逆冲型)比2017年九寨沟MS7.0地震(走滑型)的形成需要更多的应力积累,因此2013年岷县漳县MS6.6地震虽然震级较小但震前异常更显著。

     

    Abstract:
    The 2013 Minxian-Zhangxian MS6.6 earthquake and the 2017 Jiuzhaigou MS7.0 earthquake are typical moderate-strong earthquakes developed in the southeast of Gansu Province in recent years. In order to further discuss the common characteristics of geophysical anomalies before earthquakes in this area, the two earthquakes are taken as the research objects in this paper. Based on the published data, it is concluded that there are obvious geophysical anomalies before the 2013 Minxian-Zhangxian MS6.6 earthquake and the 2017 Jiuzhaigou MS7.0 earthquake, including crustal deformation (fixed-station and cross-fault leveling), electromagnetism and underground fluid. Among them, there are 49 precursory anomalies of the 2013 Minxian-Zhangxian MS6.6 earthquake and 34 precursory anomalies of the 2017 Jiuzhaigou MS7.0 earthquake. Meanwhile, the number of precursory anomalies in different disciplines are calculated and the regulations of precursory anomalies in different disciplines are summarized. Besides, the geophysical observation stations are divided according to active fault zones, and the number and percentage of precursory anomalies on relevant fault zones are counted to analyze the precursory anomalies controlled by active tectonics, which has been compared with GNSS velocity field. We also adopt Anderson fault stress model to discuss the different spatial distribution and intensity of precursory anomalies between these two earthquakes, as well as the focal mechanism effect on precursory anomalies in depth. According to the above, the following understandings are obtained:
    1) Through the comparison of the two earthquakes, the precursory anomalies of cross-fault leveling and electro-magnetism of the 2013 Minxian-Zhangxian MS6.6 earthquake are more obvious, with the respective anomaly percentages 35% and 28%, followed by fixed-station deformation and underground fluid anomalies, the anomaly percentages are 21% and 15%, respectively. While the electromagnetic anomalies of the 2017 Jiuzhaigou MS7.0 earthquake are significant, with an anomaly percentage of 45%, followed by the cross-fault leveling and fixed-station deformation, with an anomaly percentage of 26%. While the underground fluid anomalies are the least, with an anomaly percentage of only 5%. Summarized from the above data, the geophysical anomalies before the 2013 Minxian-Zhangxian MS6.6 earthquake are more significant than these of the 2017 Jiuzhaigou MS7.0 earthquake. And precursory anomalies of the two earthquakes both reflect that the electromagnetic and cross-fault leveling anomalies are more obvious, while the underground fluid precursory anomalies are rare.
    2) The distribution of geophysical anomalies before the earthquake is related to the active tectonics. Specifically, the precursory anomalies before the 2013 Minxian-Zhangxian MS6.6 earthquake are mainly concentrated in the east Kunlun-west Qinling fault zone and the Liupanshan-Haiyuan fault zone, while the precursory anomalies before the 2017 Jiuzhaigou MS7.0 earthquake are mainly concentrated in the Longmenshan fault zone and the east Kunlun-west Qinling fault zone. The east Kunlun-west Qinling fault zone, which is located in the boundary structure of the Bayan Har block, the Longxi block and the Qaidam basin, has significant precursory anomalies before these two earthquakes, indicating that as an active structure of the central orogenic belt, it plays an important role in the stress conduction of the present extension of the Qinghai-Xizang Plateau.
    3) There is a good correspondence between the distribution of precursory anomalies before the two earthquakes and the GNSS velocity field. The GNSS velocity field is the direct manifestation of the current crustal movement and fault activity. The corresponding relationship between the GNSS velocity field and the precursory anomalies distribution further proves the difference in seismogenic tectonic setting between these two earthquakes, and helps to analyze the stress accumulation before the earthquakes, as well as the energy conduction in seismogenic process.
    4) The stress mechanism of the 2013 Minxian-Zhangxian MS6.6 earthquake and the 2017 Jiuzhaigou MS7.0 earthquake are analyzed based on the Anderson fault stress model, which indicates that shear stress (corresponding to strike-slip fault) is more likely to form fault rupture than normal stress (corresponding to reverse fault), and this viewpoint is supported by rock test laboratory results: an increase in shear stress at the fault plane along the direction of fault slip makes the fault more likely to rupture, while an increase in normal stress (pressure) at the vertical fault plane increases the friction strength of the fault and inhibits rupture. Therefore, although the magnitude of the 2013 Minxian-Zhangxian MS6.6 earthquake (thrust type) is slightly smaller than the 2017 Jiuzhaigou MS7.0 earthquake (strike-slip type), it needs to accumulate more stress to rupture, showing a higher intensity of precursory anomalies.
    This study summarizes the precursory anomalies regulation of two typical earthquakes in the southeast of Gansu Province, which attributes to accumulate earthquake cases data for the establishment of prediction practice in this area.

     

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