快速且高精度的三维大地电磁法正反演是目前研究的热点.由于大地电磁法场源的平面波特性,以往的正演方法大多采用直接求解总场的方法,在边界强加二维边界条件.本文提出了一种基于二次场方法的三维大地电磁法正演算法,将平面波在层状背景模型中的响应作为场源项,得到二次场满足的偏微分方程,并利用交错网格有限差分法求取二次场.与其他学者的基于总场方法的结果的对比证明了本文采用方法的正确性.在基于二次场的正演算法基础上,实现了基于L-BFGS的三维反演方法,并对公开的数据集进行了反演.另外,针对大地电磁法的多频率观测特性,采用了基于MPI的分频并行策略对程序进行并行化,可达到接近线性的加速比.%Efficient and accurate three dimensional magnetotelluric forward modeling method has attracted increasing attention in recent years.Due to that the source of magnetotelluric is plane wave,the approach that most forward modeling method used is solving the total field directly and imposing two dimensional boundary conditions.In this work,we propose a secondary field approach for three dimensional magnetotelluric forward modeling.We use the response of plane wave of a layered background model as the source term,then we get the partial difference equation that the secondary field satisfied,staggered grid finite difference method is used to solve this equation.Comparison with others result proves the correctness of our method.Based on our forward method,we implemented a three dimensional L-BFGS inversion method and inverted two public datasets.Besides,to utilize the multi-frequency characteristic of magnetotelluric,our code has been parallelized over frequencies using MPI,this approach can achieve near linear accelerate rate.
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