基于线弹性位错模型及干涉雷达同震形变场反演1997年玛尼Mw7.5级地震参数-Ⅰ.均匀滑动反演

Parameter inversion of the 1997 Mani earthquake from INSAR co-seismic deformation field based on linear elastic dislocation model-Ⅰ. Uniform slip inversion

1997年11月8日西藏玛尼Mw7.5级地震是干涉雷达技术应用于地震观测以来的一次重要事件.Peltzer等认为该形变场体现了地壳的非线性弹性形变响应,挤压象限和拉张象限的杨氏模量比值为2.相同的情形并没有在其他地震同震形变场中发现,通常用线弹性理论就能够很好地解释观测数据.考虑到他们所用断层模型的简化程度和纯走滑约束等,本研究认为非线性弹性解释是牵强的.应用广泛使用的Okada线弹性位错模型,采用卫星观测得到的地表断层位置,去除倾滑为零的约束,基于非线性优化反演方法寻求拟合雷达观测的最佳断层几何参数和均匀滑动参数.结果表明,线弹性模型能够满意解释观测数据.断层在朝阳湖以东的段落最深达到16.5km,随着断层向两侧延伸,深度逐渐减小;反演得到的断层倾向和倾滑位移与野外调查一致;断层左旋走滑分量最大达到4.44m,同时倾滑分量在相同段达到了最大值1.1m,该量值不能忽略;反演得到的总地震矩为2.08×1020N.m,相当于矩阵级Mw7.5,与哈佛给出的2.23×1020N.m、Velasco等反演得到的1.8×1020N.m较接近.

The Nov. 8, 1997 Mani （Xizang） Mw7.5 Earthquake is an important event since Synthetic Aperture Radar Interferometry was used for earthquake studies. Peltzer et. al argued that the deformation field indicated the nonlinear elastic response of crust with a ratio of 2 between compressive and tensile elastic moduli. No other similar case appeared in co-seismic deformation field. Generally, linear elastic theory can give satisfactory explanation to the observation. Considering their excessively simplified fault model and the pure strike-slip assumption, we deem that nonlinear elasticity explanation is far-fetched. By using the widely-used Okada linear elastic dislocation model and the fault location on the surface from satellite observations, removing the zero dip-slip constraint, we seek best-fit fault geometry parameters and uniform slip vectors from radar observation based on nonlinear optimization inversion. The result shows that linear elastic model can satisfactorily explain the observation. The maximum depth of the fault reaches 16.5 km at the segment near the east side of Chaoyang Lake. The depth decreases gradually when the fault extending to the east and the west; inverted fault dipping direction and dip-slip are consistent with field investigation; the maximum strike-slip component reaches 4.44 m, and the dip-slip component also reaches its maximum 1.1 m at this segment, which can not be ignored in the inversion; the total seismic moment is 2.08 × 10^20 N·m from inversion, which equals to a Mw7.5 earthquake. The seismic moment is close to the 2.23 × 1020 N^20· m of Harvard solution and the 1.8 × 10^20 N· m of Velasco＇s inversion.