2022年1月8日青海门源M_(S)6.9地震前重力场动态变化

Dynamic gravity changes before the Menyuan,Qinghai M_(S)6.9 earthquake on January 8,2022

2022年1月8日青海门源M_(S)6.9地震前,中国地震局在青藏高原东北缘开展了多期流动重力观测,并观测到震中附近重力场随时间的变化.我们曾利用震中附近重力场变化信息在地震前对发震地点进行了较为准确的预测.本文综合利用地面绝对重力、相对重力资料,对青藏高原东北缘2018—2021年间的重力观测数据进行整体处理,系统分析了区域重力场动态变化及其与门源M_(S)6.9地震发生的关系.结合地震剪切波分裂、地壳裂隙及饱和度研究成果,进一步研究了区域重力场变化的时空分布特征及其机理.结果表明:(1)门源M_(S)6.9地震前2年累积重力变化呈现出明显的四象限分布特征,震中位于重力变化的四象限中心零等值线附近;(2)地震前重力异常持续时间与震级的关系、地震剪切波分裂产生的慢波时间延迟持续时间与震级的关系显现一致性,这种一致性表明地下流体运移可能是地震前观测到的重力变化的主要成因;(3)本次震中东南侧的显著重力变化延伸到了冷龙岭断裂东段至海原断裂一带,后期仍需要关注该地区的地震危险性.

Before the Menyuan M_(S)6.9earthquake in Qinghai province on January 8,2022,China Earthquake Administration carried out several relative gravity observations in the northeastern margin of the Qinghai-Tibet Plateau,and obtained reliable gravity data near the epicenter.We accurately predicted the location of the earthquake based on gravity changes before the Menyuan earthquake.In this study,we comprehensively processed the gravity observation data of the northeastern margin of the Tibetan Plateau from 2018to 2021,and systematically analyzed the dynamic changes of the regional gravity field and their relationship with the occurrence of the Menyuan earthquake.Combined with the seismic shear-wave splitting results and crustal pore medium,the spatial and temporal distribution characteristics of regional gravity field variation and its mechanism are further studied.The results show that:(1)gravity change presents an obvious four-quadrant distribution in two years before the Menyuan earthquake,the epicenter is located in the center of four-quadrant and near zero isoline;(2)The relationship between the gravity anomaly duration before an earthquake and the magnitude is similar to the relationship between the slow wave time-delay caused by shear-wave splitting and the magnitude,which suggests that deep fluid migration may be the main cause of gravity variation observed before earthquake;(3)The significant gravity variation in the southeast of the epicenter extends to the east section of the Lenglongling and the Haiyuan faults,which may require more attention to the seismic hazard in this area in the further.