A combined GA and DLS parallel algorithm for multimode Rayleigh wave inversion

Multichannel analysis of surface waves (MASW) is a vital method in near-surface exploration. Linear algorithms, such as damped least square method (DLS), are highly dependent on the initial model and are prone to trapping in local minima. While nonlinear algorithms such as genetic algorithm (GA) are globally optimal but inefficient, they are not very practical for complex calculations. In this paper, we propose a combined GA and DLS parallel algorithm (GA-DLS), which has a global search capability due to the GA framework, and has a quick local search capability due to the DLS parallel computing. To simulate the earth model in complex near-surface conditions, we set a low-velocity layer among a layered earth model (LVL) and a high-velocity layer among a layered earth model (HVL), we perform the inversion with DLS, GA, and GA-DLS, respectively. The comparison shows that the GA-DLS inversion gets an efficient and accurate result. Finally, we use the GA-DLS algorithm to invert the field data and achieve good results, verifying the effectiveness of the algorithm.