MIPT Summary This paper develops a method of joint inversion of seismic and gravity gradiometry data based on the concept of a Gramian stabilizer, which enforces the linear relationships between the different model parameters and their attributes or transforms. We take into account the existence of empirical linear relationships between the log density and log seismic velocity according to Gardner's equation, and use this relationship in the construction of the corresponding Gramian stabilizer. At the same time, the developed algorithm does not require a priori knowledge of the specific parameters of the correlation between the density and velocity, and instead provides the means to find these parameters from the inversion without actual measurement of the physical properties of the rock samples. The developed algorithm of joint inversion is based on modeling the seismic responses using the integral equation (IE) method. Introduction Seismic imaging is primarily based on the depth migration, which requires an accurate 3D velocity model for accurate time-to-depth conversion.