Research On FWI Of Wide-angle Refraction Data In Sumatra

The geological structure and physical properties in Sumatra are complicated and the mechanism of the earthquake and the reasons for the thrust fault slip are not clear so far.The study area in this paper is near the Simeulue Island in Sumatra,where the magnitude 9.2 earthquake in 2004 and the magnitude 8.6 earthquake in 2005 occurred.Accurate velocity modeling has always been urgently needed in this area.FWI has higher resolution and more advantages in complex areas.A good velocity can be used to explore the crustal geological structure and physics of the subduction zone.The change of nature in this area provides a basis for understanding the cause of thrust faults in the study area and the mechanism of earthquake breeding.The data used in this study is from 5 OBS near Simeulue Island which is highly sparse.This article focuses on the practical application of FWI.We first introduce the principle of full waveform inversion.The Lagrangian multiplier method is used to derive the adjoint equation and the gradient function of the model parameters.The problems in the application of FWI in the study area are solved efficiently and the specific inversion strategy process is established.In this paper,a series of seismic data processing and analysis are performed around the actual OBS seismic data.The initial model of the full waveform inversion is obtained by first-arrival wave travel time tomography;the near-offset direct wave is used for wavelet estimation.Then we conduct FWI with the simulated data modeling by actual geometry and a time window is added to increase the convergence speed.The feasibility of the full waveform inversion under sparse data conditions is verified.FWI is successfully applied to the wide-angle refraction data in Sumatra and we make an explanation and summary at last.