Gravity modelling by using vertical prismatic polyhedra and application to a sedimentary basin in Eastern Anatolia

Abstract

There are various methods suggested for modelling the geometry of sedimentary basins by using gravity anomalies in the literature. When dealing with datasets that are non-uniformly distributed across a study area, the choice of modelling method can significantly impact data reliability and computational resource usage. In this study, we present a gravity modelling approach utilizing prismatic vertical polyhedra. First, we summarize the requirement of such a method by highlighting limitations associated with a commonly employed modelling method that uses rectangular grid-following vertical prisms for modelling. By contrast, we propose a method that adapts a polygonal mesh to the distribution of input gravity data points, each polygonal mesh cell containing one data point and using polygonal grid-following vertical prisms for gravity modelling. To validate our method, we conduct tests using two synthetically constructed subsurface models – one featuring a normal fault and the other a deep basin. These are used to generate synthetic gravity observation data at irregularly spaced points that broadly follow the geology. The data are then inverted for obtaining subsurface structures by modelling with (a) rectangular prisms on a regular grid and (b) with our polygonal prisms on the tessellated grid. The inversion process involves calculating the heights of the prisms in both approaches, assuming a constant density contrast. The comparative analysis demonstrates the superior effectiveness of our approach (b). Finally, we apply our newly developed method to real gravity data recently collected from Gezin province, situated in the north-eastern region of the Lake Hazar pull-apart basin in Eastern Turkey. Our modelling results reveal previously underestimated basin geometry, suggesting the presence of an additional, previously unidentified fault to the east of Gezin, which forms the southern boundary of the basin.