2018花莲Mw 6.4级地震同震二维形变与断层触发和运动机制研究

Research of the Triggering Relation, Faulting Mechanism and Two-Dimension Coseismic Displacement of the 2018 Mw 6.4 Hualian Earthquake

本文基于ALOS-2卫星PALSAR-2 SAR升降轨数据,提取了2018年台湾花莲Mw6.4级地震同震地表形变场。构建了基于升降轨InSAR观测的地表东西向和垂向形变解算模型,反演获得2018年花莲地震同震二维形变场。结果显示,跨米伦断层垂向形变量级差异最大,其上盘相对下盘抬升量级~0.28 m,苓顶断层上盘相对下盘也存在~0.2 m的抬升变形。东西向形变场显示,最大东向地表变形位于米伦断层上盘北段,量级~0.15 m,最大西向地表变形则位于米伦断层上盘南段和苓顶断层上盘,量级~0.4 m。综合二维同震形变、库伦应力传输和反演断层滑动分布发现:2018年Mw6.4级花莲地震主震断层为西向倾斜的隐伏断层,且破裂传播至了米伦断层西侧区域,并触发了苓顶断层和米伦断层的破裂;其中米伦断层为东向倾斜高角度断层,其同震破裂以左旋走滑为主并兼具逆冲运动,苓顶断层为西向倾斜高角度断层,其同震破裂为左旋走滑兼具逆冲运动;滑移反演模型显示最大滑移量为~1.8 m,位于孕震断层地下~5.5 km深度处。

The ascending and descending ALOS-2 satellite PALSAR-2 SAR images are used to extract the coseismic surface deformation fields of the 2018 Mw 6.4 earthquake occurring in the Hualian County of Taiwan. Hereby, we present a desirable mathematical model for solving ground deformation in east-west and vertical directions based on the ascending and descending InSAR observations and achieve the two-dimensional coseismic deformation fields of the 2018 Hualian Mw 6.4 earthquake. The results show that the most significant vertical deformation is across the Milun fault, and the largest vertical displacement difference between the hanging wall and the footwall is ~0.28 m. Another distinct vertical deformation zone is found near the Lingding fault, showing the uplift of ~0.2 m of the hanging wall with respect to the footwall. The east-west deformation field shows that the northern area on the hanging wall of the Milun fault experiences the maximum eastward surface displacement with a magnitude of ~0.15 m. The maximum westward ground displacement with a magnitude of ~0.4 m can be found in both the southern hanging wall of the Milun fault and the hanging wall of the Lingding fault. Due to the comprehensive analysis of the Coulomb stress change caused by the coseismic faulting motion, spatial distribution characteristics of the two-dimensional coseismic deformation, and inverted fault slip distribution, we find that the main fault of the 2018 Mw 6.4 Hualian earthquake is a blind west-dipping fault, and it may rupture and propagate to the western side of the Milun fault, triggering the ruptures of the Lingding and Milun faults. The Milun fault dips to east with a high dip angle, and the coseismic slip is predominated by the left-lateral strike-slip with slight thrust motion. The Lingding fault is characterized by a west-dipping high-angle fault plane, presenting the left-lateral strike-slip and thrust faulting. The maximum slip magnitude is ~1.8 m, and is located at the depth of ~5.5 km of the seismogenic fault.