Interface depth modelling of gravity data and altitude variations: a Bayesian neural network approach

Abstract

Modelling of anomalous geological source from the gravity data is vital for understanding the crustal/sub-crustal interface depths and associated hazard assessment. Two-dimensional radial power spectra have usually been used to infer average depth of protuberant geological structures, which lack details of dimensional comprehension of lateral interfaces. Here in this study, we implement jointly scaled conjugate gradient-based Bayesian neural network (SCG-BNN) scheme with variogram modelling to carve out shallow and deeper interfaces of complex geological terrain of Eastern Indian Shield, India, using Bouguer gravity anomaly (BGA) and altitude variations data. Our “learner codes” uses the SCG-BNN optimization algorithm to build up a statistical model involving appropriate control parameters for the modelling of shallow and deeper interfaces. We have also compared the proposed SCG-BNN modelling results with the results of both conventional artificial neural networks (ANNs) schemes (e.g. conjugate gradient-based ANNs (CG-ANN) and SCG-ANN) and support vector regression (SVR) modelling to demonstrate the robustness of the underlying method. Comparative analysis suggests that the SCG-BNN model produced superior results than the results of CG-ANN, SCG-ANN and SVR models. The results based on SCG-BNN analysis and variogram modelling have identified the existence of three conspicuous fault structures, namely Malda–Kishanganj Fault, Munger–Saharsha Ridge Marginal Fault and Katihar Fault. The analyses also significantly minimize prediction error in three independent datasets (viz. training, validation and test), enhancing the precision of estimated shallow and deeper interface depths and thereby extenuating feasibility of “SCG-BNN” learner code. We, therefore, conclude that the underlying approach is robust to model various interface depths and generate precisely variation in the shallow and deeper interfaces with appropriate input data from altitude variation and BGA. The “SCG-BNN learner scheme” may potentially be used to exploit interface depths from several other complex tectonic regions.