基于多期DInSAR数据的2016年定结地震序列发震断层特征研究

2016年5月22日,在西藏定结县发生四次MW4~5地震,研究本序列地震的发震断层几何和运动特征对于认识周边活动断裂性质具有重要意义.由于发震地区偏远,且观测台网分布稀疏,本研究采用星载雷达干涉测量(DInSAR)技术进行了同震形变场重建,但是定结地震震级较小,单干涉像对获取的形变场受相位噪声影响较大.为了解决这一问题,本研究基于时间序列Sentinel-1A干涉数据生成多期同震与非同震干涉图,并利用叠加平均法对本次定结地震同震形变场进行重建,提取了定结2016年5月22日多次地震产生的同震累计整体形变场.基于InSAR同震形变场和区域地质特征,研究进行了滑动分布反演,确定其主要贡献的发震断层几何参数及滑动分布:断层走向为188°,倾角为43°,平均滑动角为78°,发震断层的运动性质以正断为主兼具少量左旋走滑分量,滑动主要集中在断层垂直深度0~9km处,最大滑动量约为25cm,位于断层倾向深度3km处,反演得到的矩震级为MW5.58.本研究结果表明采用星载InSAR叠加平均技术可以较好地压制相位噪声,有效提取此类中小型浅源地震同震微弱形变场.最后,我们认为本次定结地震与藏南拆离断层与申扎-定结断层的活动密切相关.

Characterizing seismogenic fault of 2016 Dingjie earthquake based on multitemporal DInSAR

On May 22, 2016, four M_W 4~5 earthquakes struck Dingjie County, Tibet, China. Studying the characteristics of the seismogenic fault is of great significance for understanding the regional tectonic. Due to the small magnitude of this earthquake, the interferometric deformation field acquired by a single interferometric pair was affected by large phase noise, especially atmospheric noise. In order to solve this problem, this study applied the multi-temporal interferograms generated by the time series Sentinel-1A SAR imagery. The co-seismic deformation field of this series earthquake was reconstructed by a temporal averaging method. We applied a geodetic inversion based on interferometric displacement map and elastic dislocation models. The slip distribution on seismogenic fault plane was estimated. The calculated the strike, dip and rake of the best solution were 188°, 43° and 78°,respectively. The result shows that accumulative displacement was created by normal faulting with some left-lateral strike slip contribution. The slip was mainly distributed between 0 km to 9 km in the depth, and the maximum amount of slip is about 25 cm at the depth of 3 km. The moment magnitude obtained by the inversion was M_W5.58. The result of this study showed that the applied temporal averaging solution with spaceborne InSAR data can effectively extract the coseismic deformation field of moderate or small -sized shallow earthquakes. The result implied that this earthquake is closely related to the activity of the Southern Tibet Detachment and Shenzha-Dingjie fault in southern Tibet.