Software development for a 3D gravity inversion and application to study of the Border Ranges Fault System, south-central Alaska

The Border Ranges Fault System (BRFS) bounds the Cook Inlet and Susitna Basins, and is an important petroleum province within south-central Alaska. A primary goal of our research is to test several plausible models of structure along the BRFS using a novel three-dimensional inversion technique utilizing gravity data, constrained with other geophysical, borehole and surface geological information. This research involves the development of 3D inversion modeling software using C++ Builder from Embarcadero\u27s XE2 Suite. The novel inversion approach directly models known geology with a priori uncertainties assigned to the geologic model to allow researchers to compare alternative interpretations. This technique was developed to evaluate three-dimensional structure in regions of complex and poorly known geology. Our software computes the density solution of a geologic structure by utilizing its location within the gravity field as well as the gridded surface files of known topography and subsurface units. The total gravitational effect of each body is calculated with a series of semi-infinite vertical line elements which improves the computational efficiency of computing forward models of structures with extremely complex geometry. The inversion algorithm considers a priori geophysical constraints and uncertainties due to gravity measurements, surface file inconsistencies, and forward calculations in the model solution. In addition, a Kalman-based filtering estimator is used to minimize our observation and processing noise. The estimator allows the a posteriori covariance matrix to avoid its dependence on the non-singularity of the Jacobian (model) matrix