Characteristics of normal-fault earthquake deformation in the Qinghai-Tibet Plateau revealed by InSAR
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摘要: 正断层在青藏高原的隆升扩展演化中发挥了重要作用. 本文使用InSAR技术处理Sentinel-1 SAR影像数据获得了2020至2021年发生在青藏高原内部3次正断型地震的同震形变场. 基于Okada弹性位错模型和形变场信息反演了断层几何参数和断层面滑动分布,精确地确定了发震断层位置. 研究结果显示高原内部的这些正断型地震均以正断层活动方式为主,但还兼有一定的走滑运动;发震断层主要为倾角<60°的次级隐伏断层,且均为浅源地震,滑动分布主要集中在12 km以上. 结合地球物理资料,我们分析认为正断型地震广泛分布在青藏高原中部和南部弥散型地块内,不局限于半地堑构造相关地区,并且正断型地震的发生更依赖于伸展环境中的重力势能. 伴随正断层活动的走滑运动也反映了青藏高原内部物质向东运移的运动学和动力学特征.Abstract:
The north-south convergence and east-west extension of the Tibet Plateau are accommodated by a series of active strike-slip and normal faults, and normal-fault earthquakes are very active in the plateau. During 2020 to 2021, there were three normal-fault earthquakes, namely, the Dingri MS5.9 (2020-03-20), Biru MS6.1 (2021-03-19), and Shuanghu MS5.81 (2021-03-30) earthquakes. These three earthquakes were evenly distributed in the middle and southern parts of the plateau, which provides a favorable case for us to study the seismic deformation characteristics using interferometric synthetic aperture radar (InSAR) technology. We used InSAR technology and Sentinel-1 SAR image data to generate the coseismic deformation field of the three normal-fault earthquakes in the Tibetan Plateau. The results showed that the normal-fault earthquakes in the plateau were not pure normal-fault types, and the coseismic deformation field showed both subsidence deformation and strike-slip deformation. Based on the Okada elastic dislocation model and the coseismic deformation fields, we constrained and inverted the geometric parameters and the slip distribution of the fault plane to accurately determine the locations of the seismogenic faults. The seismogenic faults were mainly secondary concealed faults with dip angles < 60°, all of which were shallow earthquakes. The slip distribution was mainly concentrated within 12 km. Combined with geophysical recognition, we inferred that normal-fault earthquakes are widely distributed in the Qinghai-Tibet Plateau, and not limited to areas related to half-graben structure, and that the occurrence of normal-fault earthquakes largely depends on the gravitational potential energy in the extensional environment. -
Key words:
- Qinghai-Tibet /
- normal-fault earthquake /
- InSAR /
- deformation characteristics
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图 3 定日地震InSAR形变场和模拟结果. 第一行为升轨A12的结果,第二行为降轨D121的结果. (a, e)分别为未解缠的原始干涉图;(b, f)分别为转为地表位移的同震形变图;(c, g)分别为模拟的形变场;(d, h)分别为观测值与模拟值的残差. 正值表示远离卫星的运动,负值表示靠近卫星的运动,红线表示模拟断层的地表迹线,灰线表示已知的断层迹线
Figure 3. Interferometric synthetic aperture radar (InSAR) coseismic deformation fields and fitting results of the Dingri earthquake in ascending and descending orbits
图 6 比如地震InSAR形变场和模拟结果. 第一行为升轨A143的结果,第二行为降轨D77的结果. (a, e)分别为未解缠的原始干涉图;(b, f)分别为转为地表位移的同震形变图;(c, g)分别为模拟的形变场;(d, h)分别为观测值与模拟值的残差. 正值表示远离卫星的运动,负值表示靠近卫星的运动,红线表示模拟断层的地表迹线,灰线表示已知的断层迹线
Figure 6. InSAR coseismic deformation fields and fitting results of the Biru earthquake in ascending and descending orbits
图 9 双湖地震InSAR形变场和模拟结果. 第一行为升轨A114的结果,第二行为降轨D121的结果. (a, e)分别为未解缠的原始干涉图;(b, f)分别为转为地表位移的同震形变图;(c, g)分别为模拟的形变场;(d, h)分别为观测值与模拟值的残差. 正值表示远离卫星的运动,负值表示靠近卫星的运动,红线表示模拟断层的地表迹线,灰线表示已知的断层迹线
Figure 9. InSAR coseismic deformation fields and fitting results of the Shuanghu earthquake in ascending and descending orbits
表 1 2020年3月20日定日地震震源参数
Table 1. Focal parameters of the 2020-03-20 Dingri earthquake
机构 震级 震源位置 断层面解1 断层面解2 经度/(°) 纬度/(°) 深度/km 走向/倾向/滑动角/(°) 走向/倾向/滑动角/(°) CENS MS5.9 87.42 28.63 10 160/47/-97 — USGS MW5.5 87.308 28.590 10 180/ 42/ -77 343 /49/ -101 GCMT MW5.7 87.42 28.51 12 184/ 47 /-77 345/45/-103 IPGP MW5.6 87.321 28.601 7 207/ 59/-75 360/34/-114 本文 MW5.1~5.3 87.40 28.68 3 — 319/44/-76 表 2 覆盖2020年3月20日定日地震的Sentinel-1影像信息
Table 2. Sentinel-1 image information covering the 2020-03-20 Dingri earthquake
飞行方向 轨道号 主影像日期 辅影像日期 空间基线/m 时间基线/天 升轨 12 2020-03-08 2020-03-20 −19.28 12 降轨 121 2020-03-16 2020-03-28 26.86 12 表 3 2021年3月19日比如地震震源参数
Table 3. Focal parameters of the 2021-03-19 Biru earthquake
机构 震级 震源位置 断层面解1 断层面解2 经度/(°) 纬度/(°) 深度/km 走向/倾向/滑动角/(°) 走向/倾向/滑动角/(°) CENS MS6.1 92.74 31.94 10 12/42/-121 — USGS MW5.7 92.915 31.925 8 17/ 37/ -113 225 /56/ -74 GCMT MW5.8 92.92 31.84 19.4 7/43/-103 232/ 56 /-61 IPGP MW5.7 92.899 31.906 10 353/50/-144 238/ 63 /-47 本文 MW5.6~5.7 92.88 31.95 6 — 229/54/-99 表 4 覆盖2021年3月19日比如地震的Sentinel-1影像信息
Table 4. Sentinel-1 image information covering the 2021-03-19 Biru earthquake
飞行方向 轨道号 主影像日期 辅影像日期 空间基线/m 时间基线/天 升轨 143 2021-03-12 2021-03-24 −24.59 12 降轨 77 2021-03-07 2021-03-19 −42.37 12 表 5 2021年3月30日双湖地震震源参数
Table 5. Focal parameters of the 2021-03-30 Shuanghu earthquake
机构 震级 震源位置 断层面解1 断层面解2 经度/(°) 纬度/(°) 深度/km 走向/倾向/滑动角/(°) 走向/倾向/滑动角/(°) CENS MS5.8 87.68 34.38 10 203/39/-72 USGS MW5.5 87.692 34.355 8 48/51/-48 173/55/-129 GCMT MW5.7 87.70 34.32 16.7 34/42/-62 178/54/-113 IPGP MW5.65 87.719 34.352 8 360/34/-114 207/59/-75 本文 MW5.5~5.6 87.68 34.36 4 47/54/-56 表 6 覆盖2021年3月30日双湖地震的Sentinel-1影像信息
Table 6. Sentinel-1 image information covering the 2021-03-30 Shuanghu earthquake
飞行方向 轨道号 主影像日期 辅影像日期 空间基线/m 时间基线/天 升轨 114 2021-03-22 2021-04-03 13.12 12 降轨 121 2021-03-23 2021-04-04 −21.39 12 -
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