基于交叉梯度约束的电阻率法和背景噪声法三维联合反演研究

电阻率法和背景噪声法是通过获得地下介质的电阻率和速度参数的分布来探究地球内部物质分布的非均匀性特征，联合反演可以有效地发挥两种方法的优势，减小反演多解性.本文采用有限内存拟牛顿（L-BFGS）算法实现了电阻率法和背景噪声法的单方法三维反演，然后基于电阻率和速度模型结构耦合约束，采用交替迭代方式实现了电阻率法和背景噪声法的三维联合反演.通过设计规则体组合模型和不规则体组合模型进行理论模型合成数据三维反演试算，结果表明：联合反演可以获得同时满足数据拟合差和结构更为相似的速度-电阻率模型；联合反演可以压制背景噪声单方法反演出现的假异常，获得更精细的速度结构；联合反演获得的电阻率模型对倾斜异常体、高阻覆层下方异常体、圈闭的高/低阻体等边界信息有明显的提升，有效克服电阻率法单方法反演的局限，提高深部电阻率的分辨率.

Three-dimensional joint inversion of the resistivity method and ambient noise method with cross-gradient constraints

The resistivity method and ambient noise method are the two essential ways to reveal the inner earth's inhomogeneity by imaging resistivity and velocity structure. Joint inversion of these two can effectively play their advantages and reduce the multiple solution. In this work, we used the L-BFGS algorithm to achieve the separate inversion of the resistivity method and the ambient noise method. Based on the cross-gradient structure coupling constraints, we applied an alternating iteration method to realize the joint inversion of the 3-D resistivity method and the ambient noise method. Through two sets of complex models, including regular and irregular anomaly combination, it is found that the data misfit and model differences decrease after joint inversion. The structures of resistivity and velocity models inverted with the joint inversion scheme are more similar than that with the separate method. The accuracy of the velocity model by the joint inversion is higher than that of the separate method, which can effectively suppress the false anomalies caused by the separate method. The joint inversion method overcomes limitations of the separate inversion methods. It improves the resolutions of the tilt anomalies, anomalies under the high resistivity overburden, and the trapped high/low resistivity anomalies from inversion.