Three-dimensional forward and inverse models for gravity fields based on the Fast Fourier Transform

We present two improved Fortran programs for gravity forward modeling that computes the gravity effect caused by an anomalous density structure, and for gravity inverse modeling to determine the subsurface density contrast from observed gravity anomalies. The programs are shown to work successfully in some models and compared with other programs. A practical method is also suggested to use high frequencies in inverse modeling by suppressing amplification of error included in high frequencies. Enhancement in computational speed due to the Fast Fourier Transform method makes it straightforward and useful to apply these programs to various situations (a) in geophysical interpretations that require extensive data processing of large datasets, including a wide range of density contrasts and depths, and (b) in joint studies with other geophysical approaches such as the seismic method.