InSAR数据约束下的2023年赫拉特地震序列发震断层探讨及其建筑物损毁评估

Seismogenic Fault and Building Damage of the 2023 Herat Earthquake Sequence Revelated by Radar Interferometry

2023年10月7日阿富汗西部赫拉特省在不足1 h内接连发生4次Mw 5.5+的地震,称之为“2023年赫拉特地震序列”,此次地震序列是阿富汗境内过去20多年来遭遇伤亡最严重的地震事件,研究该地震序列的发震断层几何和快速分析损坏建筑物的分布状况对理解Herat断裂系统的构造机制、保障高效救援以及灾后规划重建等工作具有重要科学意义。基于欧洲空间局Sentinel-1升降轨合成孔径雷达影像,利用InSAR技术(interferometric synthetic aperture radar)获取2023年赫拉特地震序列的同震形变场,以升降轨InSAR观测为约束,反演确定发震断层几何和断层滑动分布,并对发震构造进行分析;基于多时相InSAR相干性变化探测方法分析并提取本次震后建筑物损毁代理图(building damage proxy map,BDPM)。结果表明,升降轨同震形变场均位于Herat断裂带和Siakhubulak断裂带之间,升降轨数据观测得到的最大视线向形变量分别约为32.3 cm和58.9 cm。反演结果显示,同震位错以逆冲运动为主兼具少量右旋走滑运动,发震断层北倾,倾角约为34°;同震滑动未破裂至地表,主要发生在2~8 km深度,最大滑动量为2.5 m,位于5.3 km深度处,反演得到的矩震级为Mw 6.53。利用多源遥感数据综合分析,初步判定发震断层为Herat断裂带北侧的一个未被填图的逆冲性质的北倾断层。BDPM结果表明,该地震序列对震中40 km范围的建筑物造成较为严重的损毁,其可能是该地震引发大规模人员伤亡的直接原因。

Objective:On 7th October 2023,an earthquake sequence consisting of four Mw 5.5+earthquakes struck Herat,Afghanistan,marking it as the deadliest earthquake in the region over the last two decades.Determining the source parameters and slip distribution,and assessing the building damage are of great scientific significance for understanding the tectonic mechanism of the Herat fault system and ensuring efficient rescue work.Methods:First,the coseismic displacements of the 2023 Herat earthquake sequence was acquired using interferometric synthetic aperture radar(InSAR)based on the Sentinel-1 images.Second,the fault geometry and slip distribution are determined using the InSAR displacement field from ascending and descending tracks as a constraint,and the seismogenic fault is analyzed and discussed.Finally,a building damage proxy map(BDPM)was acquired based on the multi-temporal InSAR coherence change detection method.Results:The coseismic deformation occurred between the Herat Fault Zone and the Siakhubulak Fault Zone.The maximum line-of-sight displacements observed in the ascending and descending tracks were about 32.3 cm and 58.9 cm,respectively.The inversion results show that the coseismic dislocation is dominated by thrust faulting with a small amount of right-lateral slip movement,and the fault has not ruptured to the surface,showing a northdipping orientation with a dip of 34°.The slip was concentrated at depths of 2-8 km with a maximum slip of about 2.5 m occurring at a depth of 5.3 km.Conclusions:Through comprehensive analysis of multi-source remote sensing data,it can be preliminarily determined that the seismogenic fault is an unmapped northward thrust fault on the north side of the Herat fault zone.The results of the BDPM indicate that the earthquake sequence caused relatively severe damage to buildings within 40 km of the epicenter,which may be the direct cause of the largescale casualties caused by the event.