基于VTI介质海洋CSEM和MT数据联合反演的黄海海相残留盆地深部结构研究

Study on deep structure of the residual basin of the Yellow Sea using VTI medium Marine CSEM and MT data inversion method

黄海海相残留盆地因其地层结构和深部地质构造的复杂性,一直是我国海洋地球科学的一项研究重点,虽然针对该研究区已开展了一系列的地球物理调查,但由于高速碳酸盐岩层对地震波存在着一定的屏蔽作用,致使该海域深部地震资料品质受到较大影响.海洋电磁法不受高速屏蔽层影响,有利于获得高速屏蔽层内部及其下方的深部结构信息.海洋可控源电磁法(Controlled source electromagnetic method,CSEM)和海洋大地电磁测深(Magnetotelleric,MT)能够提供海底电性结构的互补信息,较于单一的电磁方法,二者联合可获得更为准确的海底电性分布.本文提出了基于乘积目标函数的层状垂直各向异性(Vertical anisotropic,VTI)介质海洋可控源电磁和大地电磁资料联合反演方法,该方法在迭代过程中根据数据的拟合情况自适应调整CSEM和MT数据的权重和正则化因子的权重,反演参数包括海底介质的横向电阻率、垂向电阻率和地层厚度.以南黄海地质地球物理资料为例,建立浅水环境地电模型,并结合浅水环境的高噪声背景特点进行合成数据模型测试及分析.将本文所提出算法应用于理论模型合成数据和南黄海实测资料反演,结果表明,较于单独的海洋CSEM和MT反演,联合反演方法能够较准确地重构海底地层的电性分布,提高对海底地层各向异性电阻率的分辨能力.

Due to the complexity of stratigraphic structure and deep geological structure,the Yellow Sea residual basin has always been a research focus of Marine geosciences in China.Although lots of geophysical investigations have been carried out,the quality of deep seismic data in this area has been greatly affected due to the shielding effect of high speed carbonate strata on seismic waves.The marine electromagnetic method is not affected by the high speed shielding layer,which is beneficial to obtain the deep structure information inside and below the high speed shielding layer.It is well known that controlled source electromagnetic(CSEM)and magnetotelluric(MT)data provide complementary information about the subsurface resistivity distribution;hence,it is useful to derive earth resistivity models that simultaneously and consistently fit both data sets.In this paper,a joint inversion method for Marine CSEM and MT data in layered vertical anisotropic(VTI)media is proposed based on product objective function.The method adaptively adjusts the weights of CSEM and MT data according to the data fitting during the inversion.Based on the geological and geophysical data of the Yellow Sea,we established a shallow water geoelectric model.The synthetic data was retrieved and analyzed combining with the high noise background characteristics of the shallow water.The inverse calculation examples of the synthetic data of the theoretical model and the measured data in the South Yellow Sea show that the proposed method can reconstruct the anisotropic resistivity of shallow sedimentary layers,the resistivity of basement layer,the burial depth and the vertical resistivity of thin reservoir layer more accurately.The joint inversion of marine CSEM and MT data can improve the resolution of anisotropic resistivity of seabed strata.