速度约束的海洋大地电磁聚焦反演方法

Marine MT Focusing Inversion Method Based on Velocity Constraints

本文利用海洋地震探测方法对速度、密度连续性发生变化的地层成像精度高的优点,提高海洋大地电磁(MT)反演空间分辨能力,提出速度约束的海洋MT聚焦反演方法,可以将OBS深部地震探测获得的速度结构模型作为先验信息引入到海洋MT反演目标函数的模型约束泛函中,对反演迭代过程中的电阻率模型施加速度结构约束。根据南黄海千里岩隆起区构建的速度-电阻率模型的反演测试表明,基于MGS聚焦稳定泛函的大地电磁反演方法可以得到高阻层以下的低阻层结构,速度约束下的海洋MT反演可以进一步提高对电阻率估计的精度:在速度约束信息准确的情况下,可以大幅提高海洋MT反演对电性结构的垂向分辨能力;当高速屏蔽层下不同地层波阻抗差异很小而影响速度模型精度时,该方法仍可利用速度梯度信息进行层位约束,提高相应层位识别能力。

In order to take advantage of the high accuracy of marine seismic detection method to image the strata with different velocity and density, and improve the resolution of marine magnetotelluric(MT) inversion, we proposed a velocity constrained marine MT focusing inversion method. The velocity structure model obtained from OBS deep seismic exploration is introduced into the model constraint function of the marine MT inversion objective function as a priori information to impose velocity structure constraints on the resistivity model in the inversion iteration. The inversion tests of velocity-resistivity model based on Qianliyan uplift area of the South Yellow Sea shows that the MT inversion method based on MGS focusing stabilizing functional can help to obtain the structure of low resistivity layer below the high resistivity layer, and the marine MT inversion based on velocity constraints can further improve the accuracy of resistivity estimation: when the velocity constraint information is accurate, the vertical resolution of marine MT inversion to electrical structure can be greatly improved;when the difference of wave impedance of different formations under the high-velocity shielding layer is very small, which affects the accuracy of velocity model, this method can still use the velocity gradient information to impose horizon constraint and improve the ability of horizon recognition.