基于GNSS观测的泸定M_(S)6.8地震震前变形演化特征研究

Pre-earthquake Deformation Evolution Characteristics of the 2022 Luding M_(S)6.8 Earthquake Based on GNSS Observation

利用2017—2020年中国局部GNSS速度场和地壳运动观测网络的基准站时间序列数据,从基线时间序列变化特征、多尺度地壳应变参数两方面,详细分析了2022年泸定M_(S)6.8地震前的构造变形及其演化特征,得到以下认识:(1)2021年玛多M_(S)7.4地震后,巴颜喀拉块体内部甘孜—小金、炉霍—小金基线时间序列的加速压缩,表明其边界断裂受同震破裂影响发生解耦并加速向南、东向推挤,导致鲜水河断裂南段—龙门山断裂西南段所围限的三岔口一带的应变能积累速率加快,地震危险性增加;(2)泸定M_(S)6.8地震处于大型走滑断裂带剪切应变高值边缘的弱化区、垂直于断层方向应变的张性区,表明闭锁背景下正应变的减小有利于断层破裂和地震成核。

Based on the observation of local GNSS velocity fields in China from 2017 to 2020,and the time series data from CMONOC,the tectonic deformation and evolution characteristics before the 2022 Luding M_(S)6.8 earthquake were analyzed in details,from the perspectives of baseline change characteristics and multi-scale crustal strain parameters.The following understandings were obtained:(1)The accelerated compression of baselines of Ganzi-Xiaojin,and Luhuo-Xiaojin in the Bayan Har block before the 2021 Maduo M_(S)7.4 earthquake,show that the boundary faults are decoupled and accelerated to the south and east after the co-seismic rupture,which leads to the acceleration of the strain energy accumulation rate and the increase of the seismic risk in the Sanchakou area bounded by the south section of Xianshuihe Fault and the southwest section of Longmenshan Fault.(2)The 2022 Luding M_(S)6.8 earthquake is located in the weakening zone of the high shear strain edge of the large strike-slip fault zone,and the tensile zone of the strain is perpendicular to the fault direction,which indicates that the decrease of the normal strain in the locked background is closely related to fault rupture and earthquake nucleation.