Efficient Setup of Initial Model for Solving 2D Gravity Anomaly Inverse Problem Based on the Normalized Full Gradient Method

The most important issue in solving the gravity inversion problem is to build a highly reliable initial hypothetical model related to geological boundaries from miscellaneous data sources (seismic or geological data) alongside gravity anomaly data. In many cases, however, the miscellaneous data sources are often very few, less than what is required to build a reliable initial model, yet we nevertheless have to rely heavily on gravity data. Some auxiliary analysis methods have been used to build the initial model such as Bott’s method, Euler convolution, power density spectrum and so on. In this article, we introduce a process to build the initial model for inverting a 2D gravity anomaly profile, in which the normalized full gradient method (NFG) is used to constrain the upper and lower boundaries of the gravity anomaly object. In the calculation of the NFG, we propose to calculate the upward continuation of the gravity anomaly to a certain height before calculating the NFG. Calculating the upward continuation of the gravity anomaly before calculating the NFG’s maximum value curve, allows the optimal harmonic number N to be determined with greater ease and stability. Both the upper and lower boundaries of the gravity anomaly object are estimated by choosing the appropriate harmonic number in the process of calculating the NFG. The obtained result is useful for supporting the construction of an initial model for the 2D gravity inverse problem. The analysis method is tested on a synthetic model as well as actual gravity data from the East Vietnam Sea.