基于MFMM正演和Subspace反演下2D起伏层状介质中多震相走时同时反演成像

Simultaneous traveltime tomography in 2-D undulated layered complex media: combination of modified FMM ray tracing method and subspace inversion solver

结合分区多步快速行进法(Multistage FMM)正演算法和子空间(Subspace)反演算法,形成了一种新的多震相走时同时反演成像技术(简称:FMM+Subspace).为了避免不规则界面三角网格更新后,还需重新剖分的问题,正演算法中采用不等距上行差分公式进行界面上走时的计算;同时为了避免反演未知速度参数过多,导致反演效率低下等问题,文中采用“双重网格”策略进行正、反演.为了验证所提反演方法的有效性和正确性,文中与其他反演方法(正演:分区多步不规则最短路径算法;反演:共轭梯度求解带约束的阻尼最小二乘问题:简称:ISPM+DMNCLS_CG)进行了对比分析,验证了所提反演算法的正确性和有效性.井间检验板联合反演和深地震测深联合反演、同时反演数值模拟表明:FMM+Subspace反演算法是一种行之有效的走时同时反演方法技术.

To conduct simultaneous traveltime tomography,we in this paper combine our newly developed multistage Modified Fast Marching Method(MFMM)and subspace inversion solver to formulate a simultaneous traveltime inversion method(referred as to MFMM_Subspace).We apply an uneven grid upwind differential format to calculate the traveltime near the interface to avoid of redoing the parameterization near the interface with triangular grid.Meanwhile,we adopt double grid strategy in the forwarding modeling and inversion to avoid of excessive unknown velocity parameters.To verify the computational efficiency and accuracy,we compare the proposed simultaneous inversion method with our previous developed method of ISPM+DMNCLS_CG(ISPM:irregular shortest-path method;DMNCLS_CG:conjugate gradient method to solve the damped minimum norms and constrained least squires problem).The synthetic inversion results of crosshole checkerboard test and deep seismic sounding show that the MFMM_Subspace is an effective simultaneous traveltime inversion method.