摘要
In this paper,using natural earthquake P-wave arrival time data recorded by the seismic network in the surrounding area of Madoi,the three-dimensional fine P-wave crustal velocity structure at depths above 60 km in the epicenter of the Madoi Ms7.4 earthquake was inverted using the double-difference seismic tomography method.On the basis of the relocation of the source of the aftershock sequence,we summarized the strip-shaped distribution characteristics along the strike of the Jiangcuo fault,revealing the significant heterogeneity of the crustal velocity structure in the source area.Research has found that most of the Madoi Ms7.4 aftershocks were located in the weak area of the high-speed anomaly in the upper crust.The focal depth changed with the velocity structure,showing obvious fluctuation and segmentation characteristics.There was a good correspondence between the spatial distribution and the velocity structure.The high-velocity bodies of the upper crust in the hypocenter area provided a medium environment for earthquake rupture,the low-velocity bodies of the middle crust formed the deep material,and the migration channel and the undulating shape of the high-speed body in the lower crust corroborated the strong pushing action in the region.The results confirmed that under the continuous promotion of tectonic stress in the Madoi area,the high-speed body of the Jiangcuo fault blocked the migration of weak materials in the middle crust.When the stress accumulation exceeded the limit,the Madoi Ms7.4 earthquake occurred.Meanwhile,the nonuniform velocity structure near the fault plane determined the location of the main shock and the spatiotemporal distribution of the aftershock sequence.
本文基于玛多周边地区地震台网记录的天然地震P波到时数据,利用双差地震层析成像方法,反演了玛多Ms7.4地震震源区域60km以上深度的地壳三维精细P波地壳速度结构,并在对余震序列震源位置进行重定位的基础上总结了沿江错断裂走向的条带状分布特征,揭示了震源区域地壳速度结构的显著不均匀性。研究发现玛多Ms7.4的余震活动大多位于上地壳高速异常体中容易破裂的薄弱区,震源深度随速度结构变化,表现出明显的起伏、分段特征,空间分布与速度结构之间存在良好的对应关系。分析认为震源区域的具体机理为上地壳的高速体为地震破裂提供了介质环境,中地壳的低速体形成了深部物质的运移通道,下地壳高速体的起伏形态佐证了区域内承受的强烈推挤作用。研究证实玛多地区在构造应力的持续推动下,江错断裂的高速体阻挡了中地壳软弱物质的运移,当应力累积超出了承受限度时,导致了玛多Ms7.4地震的发生。同时,断层面附近非均匀的速度结构决定了主震的发震位置和余震序列的时空分布。
基金
support:Seismic Regime Tracking Project of CEA (2023010123)
Combination Project with Monitoring,Prediction and Scientific Research of Earthquake Technology,CEA (3JH-202302019).
