2021年青海玛多M_(W)7.3地震InSAR的同震形变场、断层滑动分布及其对周边区域的应力扰动

COSEISMIC DEFORMATION FIELD,SLIP DISTRIBUTION AND COULOMB STRESS DISTURBANCE OF THE 2021 M_(W)7.3 MADUO EARTHQUAKE USING SENTINEL-1 INSAR OBSERVATIONS

文中基于D-InSAR技术,利用欧空局C波段升降轨哨兵SAR数据,获取了2021年5月22日青海玛多M_(W)7.3地震的InSAR同震形变场,并对同震形变的空间特征、量级和断层破裂的分段性进行了分析。哨兵卫星的高质量观测数据清晰地描绘了玛多地震的地表破裂迹线,地表破裂长度约210km。为了进一步认识玛多地震断层深部的同震滑动分布特征和发震断层几何性质,基于升、降轨InSAR形变场及精定位余震数据确定的断层几何反演了同震滑动分布,并基于同震库仑应力变化分析了本次地震对周边区域的应力扰动。结果表明,玛多M_(W)7.3地震发生在巴颜喀拉块体内部的一条次级断层上,且与东昆仑断裂带的主断裂近平行,结合野外考察、地质资料和InSAR地表破裂迹线确定的发震断层为昆仑山口-江错断裂。玛多地震产生的同震形变场空间影响范围广,形变场的长轴呈NWW向,升、降轨观测的形变量符号相反,结合哨兵数据的观测几何确定发震断层的运动性质以左旋走滑为主。基于升、降轨InSAR数据得到的最大视线向(Line of Sight,LOS)形变量约为0.9m。同震滑动分布模型显示,整体上断层的走向为276°,倾角为80°,倾向NE,最大滑移量约为6m,平均滑动角为4°,矩震级为M_(W)7.45,地震主体破裂发生在0~10km深度范围内,同震破裂至地表,与野外考察所观测到的广泛分布的同震地表破裂带一致。以玛多-甘德断裂为接收断层的同震库仑应力模型显示,玛多地震在玛多-甘德断裂西段附近产生了明显的应力降,表明玛多地震释放了玛多-甘德断裂的库仑应力,导致后者的地震危险性可能大大降低;而在玛多-甘德断裂和昆仑山口-江错断裂交叉的区域存在应力加载效应,但考虑到玛多地震的余震会释放多余的能量,该区发生较大地震的危险性可能降低。以东昆仑断裂为接收断层的同震库仑应力模型显示,玛多地震在东昆仑断裂东段附近产生了明显的应力加载效应,结合该段震间较高的应变率特征,其地震危险性需要引起关注。

InSAR coseismic deformation fields caused by the Maduo M_(W)7.3 earthquake occurring on May 22,2021 were generated using the C-band Sentinel-1A/B SAR images with D-InSAR technology.The spatial characteristics,magnitude of coseismic deformation and segmentation of the seismogenic fault were analyzed.The surface rupture trace was depicted clearly by InSAR observations.In addition,the coseismic slip distribution inversion was carried out constrained by both ascending and descending InSAR deformation fields and relocated aftershocks to understand the characteristics of deep fault slip and geometry of the seismogenic fault.The regional stress disturbance was analyzed based on coseismic Coulomb stress change.The results show that the Maduo M_(W)7.3 earthquake occurred on a secondary fault within the Bayan Har block which is almost parallel to the main fault trace of the Kunlun Fault.According to field investigation,geological data and InSAR surface rupture traces,the seismogenic fault is confirmed to be the Kunlunshankou-Jiangcuo Fault.The rupture length of seismogenic fault is estimated to be~210km.The NWW direction is followed by the overall displacement field,which indicates a left-lateral strike-slip movement of seismogenic fault.The maximum displacement is about 0.9m in LOS direction observed by both ascending and descending InSAR data.The inversion result denotes that the strike of the seismogenic fault is 276°and the dip angle is 80°.The maximum slip is about 6m and the average rake is 4°.The predicted moment magnitude is M_(W)7.45,which is overall consistent with the result of GCMT.An obvious slip-concentrated area is located at the depth of 0~10km.The coseismic Coulomb stress change with the East Kunlun Fault as the receiver fault shows that the Maduo earthquake produced obvious stress increase near the eastern segment of the East Kunlun Fault.Thus the seismic risk increases based on the high interseismic strain rate along this segment,which should receive more attention.In addition,the coseismic Coulomb stress change with the Maduo-Gande Fault as the receiving fault indicates that the Maduo earthquake produced an obvious stress drop near the western part of the Maduo-Gande Fault,which indicates that the Maduo earthquake released the Coulomb stress of the Maduo-Gande Fault,and its seismic risk may be greatly reduced.However,there is a stress loading effect in the intersection area of the Maduo-Gande Fault and the Kunlunshankou-Jiangcuo Fault.Considering that aftershocks of Maduo earthquake will release excess energy,the greater earthquake risk may be reduced.