基于交叉梯度约束的大地电磁与地震面波二维联合反演研究

Recently, it is becoming a common phenomenon that magnetotelluric and seismic surface wave detection have been applied to study the same region at the same time. Due to the multiplicity of inversion, the results inverted by signal methods can be very different, which causes great trouble in integrated interpretation. In this project, we propose the study of joint inversion of magnetotelluric and seismic surface wave to solve this problem. We adopt the way from study of improved single inversion method to joint inversion method, and realize direct inversion algorithm of two-dimensional profile velocity structure for surface dispersion data, automatically searched Lagrange multiplier of non-linear conjugate gradient algorithm for two-dimensional magnetotelluric data, joint inversion of magnetotelluric and surface dispersion data with cross-gradient method. The signal inversion algorithm and joint inversion algorithm is performed by generated data of theoretical models to check the robustness, effectiveness of the inversion algorithms, and compared to the results of single inversion algorithm to verify superiority of joint inversion method. Finally, we present jointly inverted models of electrical resistivity and S-wave velocity for a two-dimensional profile from Tanghai to Shangdu centered on North China Block, which can verify the applicability of the signal inversion method and joint inversion method. Through the studies in the project, we can provide an advanced inversion technology to detect fine-structure of velocity and resistivity by joint inversion of magnetotelluric and seismic surface wave.

近年来，在同一区域同时开展大地电磁和地震面波的研究实例逐渐增多，但由于反演的多解性，这两种方法单独反演的结果往往差异很大，给综合解释带来困扰。为了解决这个难题，本项目提出开展大地电磁和地震面波的联合反演研究。采用“先完善单一方法反演，再研究联合反演”的思路，依次实现面波频散直接反演二维剖面速度结构算法、自动搜索拉格朗日乘子的二维大地电磁非线性共轭梯度反演算法、交叉梯度约束的大地电磁与地震面波二维联合反演算法。对多种理论模型合成数据进行单独反演和联合反演试算，检验反演算法的稳定性和有效性，以及联合反演算法的优越性。最后对华北克拉通唐海-商都剖面实测大地电磁和地震面波数据进行处理和反演，检验单独反演和联合反演算法的实用性。本项目研究成果将为大地电磁和地震面波二维联合探测获得精细地下速度和电阻率结构提供先进反演技术手段。

近年来，在同一工区同时开展大地电磁和地震面波勘探的实例逐步增多。由于反演的多解性，同一工区两种方法的资料单独反演的结果往往差异大，给综合解释带来困扰。为了解决这个难题，充分发挥两种方法的优势，本项目提出开展大地电磁和地震面波联合反演研究。项目组成员经过3年的努力完成了：（1）开发了面波频散直接反演二维剖面速度结构的算法；（2）开发了自动搜索拉格朗日乘子的二维大地电磁非线性共轭梯度反演算法；（3）基于交叉梯度约束开发了大地电磁与地震面波二维联合反演算法。通过理论模型合成数据试算和实测数据的应用，结果发现基于交叉梯度耦合约束的联合反演算法适用于速度和电阻率结构耦合反演约束反演，在联合反演过程中，当两种物性相似性高的区域，会通过交叉梯度项相互制约、相互影响，有效地实现大地电磁和面波两种方法的优势互补,从而提高反演精度。本项目研究成果可为大地电磁和地震面波二维联合探测获得精细地下速度和电阻率结构提供理论基础。