Afterslip distribution of 2017 Iran MW7.3 earthquake and its triggering effects on the 2018 MW6.0 earthquake
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摘要: 收集了覆盖监测区域的Sentinel-1卫星雷达影像，利用短基线集干涉测量技术提取了2017年伊朗萨波尔扎哈布MW7.3地震后283天的地表时序形变，通过二步法反演得到其震后余滑分布，之后采用差分干涉技术获取了2018年发生于同一地区的贾万鲁德MW6.0地震的同震形变场，并将反演所得的发震断层参数作为应力计算的接收断层参数，来分析2017年MW7.3强震及其震后活动对2018年贾万鲁德MW6.0地震的触发影响。结果表明：萨波尔扎哈布地震的震后形变主要由孕震断层面的余滑运动所致，震后283天余滑模型的累积滑移量达到0.7 m；2018年贾万鲁德地震的发震断层走向为355.6°，倾角为89.4°，同震断层破裂以右旋走滑为主，兼具部分正断层运动。本文所得的贾万鲁德地震断层平面上的库仑应力变化表明，2017年MW7.3主震及其震后余滑对2018年MW6.0地震的发生具有一定的触发效应，MW6.0地震的发生可能与区域板块的活动性相关。Abstract: In this study, a set of radar images acquired by the Sentinel-1 satellite that covers the interested seismically-effected area were collected. The time-series surface deformation of the 283-day time span after the 2017 Sarpol Zahab, Iran, MW7.3 earthquake was extracted by using small baseline subset technique, then the two-step procedure inversion is carried out to obtain the afterslip distribution. In order to analyze the triggering effects of the 2017 strong earthquake and its post-seismic faulting on the 2018 Javanrud MW6.0 earthquake, the coseismic deformation field covering the whole MW6.0 earthquake region was obtained by using differential interferometry technique, and the inversion results of seismogenic fault parameters were used as receiving fault parameters for stress calculation. The results show that the post-seismic deformation of the Sarpol Zahab earthquake is mainly dominated by the afterslip effect. 283 days after the earthquake, the accumulative slip of the after-slip model reaches up to 0.7 m. The coseismic source model of the Javanrud MW6.0 earthquake indicates that the seismogenic fault strike is 355.6°, the dip angle is 89.4°, and the rupture of coseismic fault is characterized by the right-lateral strike-slip together with some normal dip-slip component. Moreover, the calculated Coulomb stress change suggests that the MW7.3 earthquake and its afterslip have triggering effect on the subsequent Javanrud MW6.0 earthquake, and the occurrence of Javanrud earthquake could also be contributed by the regional plate activity.
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图 1 2017 年和 2018 年两次伊朗地震震源区的构造背景及余震分布
Figure 1. Tectonic settings of the source regions of the two Iran earthquakes in 2017 and 2018 and aftershock distribution
图 2 2017年萨波尔扎哈布MW7.3地震的震后形变场
（a） 升轨视线向形变量；（b） 降轨视线向形变量
Figure 2. Post-seismic deformation field of the Sarpol Zahab MW7.3 earthquake in 2017
（a） Ascending LOS deformation；（b） Descending LOS deformation
图 3 点形变序列（a）及震后余滑的地震矩张量M0和矩震级MW随时间的变化（b）
Figure 3. Point deformation sequences （a） and variation of the seismic moment tensor M0 and the moment magnitude MW of the afterslip with post-seismic time （b）
图 4 2017年萨波尔扎哈布MW7.3地震的震后余滑分布
Figure 4. The afterslip distribution of Sarpol Zahab MW7.3 earthquake in 2017
图 5 2017年萨波尔扎哈布MW7.3地震震后余滑的模拟形变场和残差。（b） 降轨形变场
Figure 5. The simulated post-seismic deformation fields and the residuals based on the afterslip of the Sarpol Zahab MW7.3 earthquake in 2017。（b） The descending deformation field
图 6 2018年贾万鲁德MW6.0地震升轨（上）、降轨（下）的同震形变场及其模拟残差
（a） 观测形变场；（b） 模拟形变场；（c） 残差
Figure 6. Coseismic deformation fields and simulation residuals in ascending （upper） and descending （lower） orbits of the Javanrud MW6.0 earthquake in 2018
（a） Observed InSAR deformation field；（b） Simulated deformation field；（c） Residual
图 7 InSAR反演所得的贾万鲁德MW6.0地震的断层滑动模型
（a） 断层滑动空间分布；（b） 断层平面上的滑动分布，黄色星形代表2018年贾万鲁德MW6.0地震震源在断层面上的投影位置
Figure 7. Fault slip model of the Javanrud MW6.0 earthquake constrained by InSAR observations
（a） 3D view of the fault slip；（b） Slip distribution on the fault plane，where the yellow star represents the projected location of the hypocenter of the 2018 MW6.0 Javanrud earthquake
图 8 2017年萨波尔扎哈布MW7.3地震及其震后余滑在2018年贾万鲁德MW6.0地震发震断层上触发的库仑应力变化∆CFS
（a，b） MW7.3地震对 MW6.0地震触发的库仑应力变化∆CFS；（c，d） MW7.3地震的震后余滑对MW6.0地震触发的库仑应力变化∆CFS；（e，f） 本文计算使用的2017年MW7.3地震同震断层模型（Yang et al，2018b）。图中黄色和红色星形分别代表2018年MW6.0和2017年MW7.3地震震源在各自断层面上的投影位置
Figure 8. The Coulomb failure stress change ∆CFS on the fault plane of 2018 MW6.0 earthquake triggered by the 2017 MW7.3 earthquake and its afterslip
（a，b） ∆CFS on the seismogenic fault plane of the MW6.0 earthquake triggered by the MW7.3 earthquake；（c，d） ∆CFS on the fault plane of the MW6.0 earthquake triggered by the MW7.3 earthquake afterslip；（e，f） The coseismic fault of the 2017 MW7.3 earthquake used in the calculation of ∆CFS （Yang et al，2018b）。 The yellow and red stars represent the projected location of the hypocenter of the 2018 MW6.0 and the 2017 MW7.3 events on their fault planes
图 9 2017年MW7.3 地震的同震及震后断层滑动分布
Figure 9. The co- and post-seismic fault slip distribution of the 2017 MW7.3 earthquake
表 1 Sentinel-1A卫星的SAR影像参数
Table 1. SAR image parameters of Sentinel-1A satellite
轨道方向 监测时段 影像数量 波长/cm 飞行角/° 入射角/° 分辨率/m 升轨 2017-11-23—2018-08-14 12 5.6 −9.7 39.2 5×20 降轨 2017-11-19—2018-08-22 13 5.6 −167.0 43.9 5×20 
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表 2 Sentinel-1B卫星SAR影像参数
Table 2. SAR image parameters of the Sentinel-1B satellite
卫星类型 轨道方向 获取时间 飞行角/° 入射角/° 垂直基线/m 震前日期 震后日期 Sentinel-1B 升轨 2018-08-15 2018-08-27 −12.9 33.8 50.6 Sentinel-1B 降轨 2018-08-16 2018-08-28 −166.9 39.2 −22.6
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