中小地震三维形变场重构方法研究与同震滑动分布反演——以2016年5月22日定日MW5.3地震为例

地震三维形变场对于研究地震发震机制等具有重要意义。 已有的InSAR三维形变场重构研究中, 只有中强地震的实例。 由于形变量级小、 InSAR方位向形变的误差较大, 中小地震的三维形变场重构易受噪声等影响。 本文以2016年5月22日西藏定日M_W5.3地震为例, 开展中小地震三维形变场重构的尝试。 首先基于InSAR技术获取了Sentinel-1升轨和降轨观测模式下的同震形变场, 再结合同震形变场的特点、 区域构造特征等, 添加限定方程(走滑运动为0), 重构了同震三维形变场。 结果显示, 震中附近以下降为主, 幅度达7 cm, 南北方向形变较小(约2 mm), 此区域还伴有2 cm的西向水平运动; 形变中心区域东西两侧部分区域均出现少许东向运动(1.5 cm)。 由同震形变场特征判断此次地震以正断破裂为主。 本文提出了基于连续性分层采样选取样本点方法, 以适应本地震形变场的实际情况。 对所得的LOS向位移场和重构的三维形变场进行降采样, 反演得到了断层面上的滑动分布, 两种数据得到的结果相似, 最优发震断层的走向约181°, 倾角约45°, 断层错动平均滑动角约-87.1°, 平均滑动量约为3.6 cm, 最大滑动量位于深度6.5 km处, 相当于一次M_W5.4的地震。

Research on Reconstruction Method of Three-Dimensional Deformation Field for Small and Medium Earthquakes and Inversion of Co-seismic Slip DistributionA case study of May 22 2016 MW5.3 Dingri earthquake

Three-dimensional seismic deformation field is of great significance to the study of earthquake mechanism. It has been successfully reconstructed for only moderate or strong earthquakes in previous research. For small and medium earthquakes, the reconstruction of three-dimensional deformation field is vulnerable to noise and other effects, due to the small magnitude of displacement, and the large uncertainty in InSAR’s azimuthal deformation. Taking the May 22, 2016 Dingri M_W5.3 earthquake as an example, we attempt to reconstruct its three-dimensional deformation field. Firstly, the coseismic deformation field of the earthquake is obtained by using InSAR technology under the ascending and descending observation mode of Sentinel-1. According to the characteristics of coseismic deformation field, regional structure and so on, the three-dimensional deformation field of co-seismic is reconstructed by adding a limited equation (strike-slip motion is 0) in it. The results show that: the subsidence mainly distributes near the epicenter with the maximum amplitude reaching 7 cm, and the deformation in the north-south direction is small (about 2 mm), while accompanied by a horizontal westward motion of 2 cm; small eastward motions (1.5 cm) occur in the west and east parts of the deformation center region. From the deformation characteristics, the earthquake is illustrated as normal fault movement. In view of the characteristics of the seismic deformation field, a more suitable resampling point selection method based on continuous stratified sampling is proposed in this paper. Taking down-sample from the LOS displacement field and the reconstructed three-dimensional deformation field, the slip distribution on the fault plane is obtained, and the results from two data are similar. The best strike of the fault is about 181°, the optimal dip angle of the seismogenic fault about 45°, the average slip direction of the fault dislocation being about -87.1°, and the average slip is 3.6 cm. The maximum slip is located at a depth of 6.5 km. The observed fault slip is equivalent to an earthquake with a moment magnitude of M_W5.4.