Geophysical structure of a local area in the lunar Oceanus Procellarum region investigated using the gravity gradient method

Abstract

Compared to gravity method, the gravity gradient has multi-component advantages and can emphasize short wavelength features. By providing more detailed features in the image display, it could present a more accurate determination of the spatial distribution of the underling anomaly body. In our study, based on the gravity gradient data that was synthesized from the high-precision gravity model from Gravity Recovery and Interior Laboratory mission, we analyzed the tectonic structure of the Moon’s shallow layers in Oceanus Procellarum region. Bouguer anomalies of gravity gradient are used for geological boundary recognition and three-dimensional density inversion. Theta Map method is adopted for the edge identification of geological structures. It fully utilizes the characteristics of multi-components combination of gravity gradient to sharpen the boundaries identification of abnormal bodies. During the density inversion, in order to decrease the non-unique solution problem, the depth weight constraint is added to the inversion equation. Furthermore, the method of wavelet coefficient compression and Least Squares QR-decomposition is applied to accelerate the inverse calculation of large ill-conditioned equations. According to the result illustration, we found that: 1) The combination of gravity tensors has a strong boundary recognition ability in the horizontal direction. There is close consistency with the results of density inversion. 2) Our study supports the expansion and intrusion hypothesis of lunar magma in the research zone of Oceanus Procellarum, since the distribution of density tomography results at different depths is higher than the normal assumed crust density of the Moon in the majority of areas. Moreover, the intrusion source in our research area is concentrated at a direction depth of 30–45 km below the mean lunar radius surface approximately.