• ISSN 2097-1893
  • CN 10-1855/P

2020年尼玛MW6.3地震同震及震后断层滑动特征

Coseismic and postseismic fault slip characteristics of the 2020 MW6.3 Nima earthquake

  • 摘要: 2020年尼玛MW6.3地震发生在青藏高原羌塘块体依布茶卡地堑北部. 震中区域地质构造、地形地貌复杂,近场地面观测台站、数据较少. 合成孔径雷达干涉测量(Interferometric Synthetic Aperture Radar, InSAR)技术具有全天侯、大范围、高空间分辨率等监测优势,能够弥补近场地面形变观测的不足. 然而,已有研究对该次地震发震断层、同震及震后断层滑动特征的观点存在差异,且仅采用运动学模型提取震后断层余滑特征. 本文利用哨兵1号(Sentinel-1)卫星升、降轨合成孔径雷达(Synthetic Aperture Radar, SAR)影像和差分干涉测量技术提取该次地震不同视角的同震形变场,基于弹性半空间位错模型反演地震同震断层几何及滑动分布,采用应力驱动的震后余滑模型对震后断层滑动进行建模分析,并且探讨了地震发震断层及断裂带摩擦属性特征. 结果表明,升、降轨InSAR同震形变场在震中区域连续光滑、整体呈NNE-SSW走向,断层南东侧区域形变均较为显著且沿视线向以下降为主. 同震断层破裂以正断为主,兼有左旋走滑分量,走向角为31.43º,倾角为45.79º,同震断层滑动主要位于地下3.58~10.75 km,最大滑动量为1.33 m,矩震级为MW6.33. 应力驱动的震后余滑模型能够较好地解释尼玛MW6.3地震近6个月的InSAR震后形变场,震后余滑主要发生在同震断层显著滑动区域南西段的上侧、下侧及南西侧,最大值为47.2 cm. 尼玛MW6.3地震发震断层可能为位于依布茶卡—日干配错断裂中部、倾向SEE的正断层,发震断裂带摩擦属性可能非均匀.

     

    Abstract: The 2020 MW6.3 Nima earthquake occurred in the northern Yibug Caka graben on the Qiangtang Block of the Tibetan Plateau. The epicentral area has complex geological structures, topography, and geomorphology, and there are few near-field ground observation stations and data. Interferometric Synthetic Aperture Radar (InSAR) has all-weather, wide ranging and high spatial resolution monitoring advantages, which can make up for the shortage of near-field ground deformation observations. However, previous studies have obtained different viewpoints regarding the seismogenic fault and coseismic and postseismic fault slip characteristics of this event. In addition, only the kinematic model has been used to extract the postseismic fault afterslip characteristics. In this study, we used ascending and descending Sentinel-1 Synthetic Aperture Radar (SAR) images and differential interferometry technology to extract the coseismic deformation fields at different viewing angles. The coseismic fault geometry and slip distribution were then inverted based on an elastic half-space dislocation model. The stress-driven postseismic afterslip model was used to model and analyze the postseismic fault slip. Finally, the earthquake seismogenic fault and the friction property characteristics of seismogenic fault zone were discussed. The ascending and descending InSAR coseismic deformation fields were continuous and smooth around the epicenter, trending NNE-SSW overall. The deformation on the southeastern side of the fault was relatively significant, and mainly decreased along the line-of-sight direction. The coseismic fault rupture was mainly normal, with a sinistral strike-slip component. The strike angle was 31.43°, and the dip angle was 45.79°. The coseismic fault slip was mainly located at 3.58-10.75 km underground, with a maximum slip of 1.33 m, and the moment magnitude was MW6.33. The stress-driven postseismic afterslip model could better explain the almost six-month InSAR postseismic deformation field of this event. The postseismic afterslip mainly occurred on the upper, lower and southwestern sides of the southwestern segment of the significant slip area of coseismic fault, with a maximum afterslip of 47.2 cm. The seismogenic fault of this event might be a normal fault located in the middle of the Yibug Caka-Riganpei Co fault and dipping SEE, and the friction property of the seismogenic fault zone might be uneven.

     

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