Magnetotelluric and gravity joint inversion using Gramian constraints integrated with strategy of wide-range petrophysical constraints

Integration of wide-range petrophysical constraints can facilitate the coupling of petrophysical parameters within a certain range, has certain fault tolerance, and is easy to implement. Nevertheless, this approach is currently only implemented in global optimization algorithms. The strategy for extending the wide-range petrophysical constraints to gradient optimization algorithms remains unresolved. In addition, although Gramian constraints depend on prior information to a small extent, the utilization of explicit related information of petrophysical parameters is low. Thus, we propose the strategy of wide-range petrophysical constraints suitable for gradient optimization algorithms, namely, "petrophysical property correlation plus range constraints and coupling terms". We also realize the joint inversion of magnetotelluric (MT) sounding and gravity based on the new strategy using conjugate gradient algorithm combined with Gramian constraints. Model tests show that the strategy can improve the utilization of prior information, and effectively limit the range of the coupling of petrophysical parameters. This method is also applied to the Chating copper-gold deposit in Anhui province and the joint inversion results clearly reveal the spatial distribution of copper-gold deposit.