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Based on the studies of simulated annealing algorithm, the continuous model space of the very fast simulated annealing was transformed to a variable discrete form in this paper. It can be proved by theoretical models that 5 to 10 times calculation work load can be saved. With a purpose to suit the needs of joint inversion, the 'single judge' error checking rule of the very fast simulated annealing algorithm was developed to the 'double judge' error checking rule to avoid the judge mistakes made by Metropolis accepting rule. Then, onedimensional and two-dimensional multi-parameters joint inversion of magnetotelluric and seismic data under the uneven topography conditions were put forward. Furthermore, the example calculation results of the theoretical models and real observed data illustrated that this constraint joint inversion technique was quite effective.

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SUMMARY Most 3‐D magnetotelluric (MT) inversions are classified as a regularized inversion with a smoothness constraint. These inverse algorithms provide smooth solutions but cannot clearly image sharp geo‐electrical interfaces. In this paper, we introduce the minimum gradient support (MGS) functional to regularize the 3‐D MT inverse problem. This functional has a property whereby the functional seeks a structure with minimum volume containing large conductivity gradients. Therefore, the MGS functional can be used to search for a model with a sharp boundary. We apply the MGS functional to 3‐D MT inversion to obtain a clear and accurate image of geo‐electrical interfaces. In addition, the modified scattering equation approach introduced in the modified iterative dissipative method (MIDM) is applied to forward calculation, which is based on integral equation (IE) formulation and allows us to efficiently reduce the time required for forward calculation with high accuracy. The quasi‐Newton iterative method is used to optimize the objective functional. It is a kind of iterative method with simplified calculation of the inverse Hessian matrix using Broyden–Fletcher–Goldfarb–Shanno (BFGS) update. The convergence of this iterative method is guaranteed with inexact line searches. We also modify the adaptive approach for optimum selection of the regularization parameter so as to fit the inverse algorithm of this study. Three synthetic models are investigated, and the obtained results are compared with those obtained by a smoothing inversion. Based on the comparison, we confirm that the MGS inversion can provide higher resolution when geo‐electrical interfaces are sharp. This property will help us to determine reliable electrical structures by the MT exploration method.

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The fine seismic velocity structure, electrical conductivity structure and geometrical construction of the crust in Shanghai region and the coupled relationship between the deep and shallow structures are investigated by using multi‐geophysics exploration methods, such as shallow seismic reflection, deep seismic reflection, highresolution seismic refraction, deep seismic wide angle reflection/refraction and magnetotelluric sounding. This experiment is the first high‐resolution comprehensive deep survey profile in Shanghai and its conjoined regions. The research results indicate that the crust in the region can be divided into three layers, namely upper crust, middle crust and lower crust. The upper crust is 12~14 km thick with a seismic velocity of 5.7~5.9 km/s, the middle crust is about 10 km thick with a velocity of 5.9~6.2 km/s and the lower crust is 10~11 km thick with a velocity of 6.2~6.3 km/s. The depth of Moho in the region is 31~33 km. There is a thin velocity gradient layer (about 6 km thick) in the upper part of the lower crust, but the velocity gradient becomes greater near the Moho interface. There are 12 main faults interpreted in the experimental profile. Except for three faults, which have dislocated G interface (crystal basement) and extended below the bottom interface (whose depth is about 10 km) of the upper crust, the other faults have ended above G interface at 3 to 5 km depth, or have converged at G interface. Moreover, there is only a high conductivity layer (about 2 km thick) within crust at 13~15 km depth. Therefore, there is no deep structure condition for potential big earthquakes in the local region. However, the active rupture zones near the Earth's surface are potential seismic source zone.