Non-linear stochastic inversion of gravity data via quantum-behaved particle swarm optimisation: application to Eurasia-Arabia collision zone (Zagros, Iran)

Potential field data such as geoid and gravity anomalies are globally available and offer valuable information about the Earth's lithosphere especially in areas where seismic data coverage is sparse. For instance, non-linear inversion of Bouguer anomalies could be used to estimate the crustal structures including variations of the crustal density and of the depth of the crust-mantle boundary, i.e. Moho. However, due to non-linearity of this inverse problem, classical inversion methods would fail whenever there is no reliable initial model. Swarm intelligence algorithms, such as Particle Swarm Optimization (PSO), are a promising alternative to classical inversion methods because the quality of their solutions does not depend on the initial model, they do not use the derivatives of the objective function, hence allowing the use of L1 norm, and finally they are global search methods, meaning the problem could be non-convex. In this paper, Quantum-behaved Particle Swarm (QPSO), a probabilistic swarm intelligence-like algorithm, is used to solve the non-linear gravity inverse problem. The method is first successfully tested on a realistic synthetic crustal model with a linear vertical density gradient and lateral density and depth variations at the base of crust in the presence of white Gaussian noise. Then, it is applied to the EIGEN 6c4, a combined global gravity model, to estimate the depth to the base of the crust and the mean density contrast between the crust and the upper-mantle lithosphere in the Eurasia-Arabia continental collision zone along a 400 km profile crossing the Zagros Mountains (Iran). The results agree well with previously published works including both seismic and potential field studies. This article is protected by copyright. All rights reserved