Refraction Waves Full Waveform Inversion of Deep Reflection Seismic Profiles in the Central Part of Lhasa Terrain

Abstract:

At present, the velocity imaging methods for deep reflection seismic data are mainly velocity analysis and tomography. Both of these methods only use the travel time information of the seismic wavefield, resulting in low resolution of velocity imaging. The full waveform inversion (FWI) method can simultaneously use the kinematic information (travel time) and dynamics information (amplitude and phase) of the seismic wavefield. Most of the current researches about FWI using deep reflection seismic data are for marine seismic data, and there is no result for continental full crust velocity structures obtained by FWI of deep reflection seismic data on land.

In this research, we mainly use the travel time and phase information of seismic waves for deep reflection seismic data inversion. Due to the strong energy of the seismic source used in the deep reflection seismic method, when there are interfaces with strong velocity contrasts in the shallow subsurface, significant multiple reflections or refractions will occur. Therefore, we propose to make full use of the multiple refraction information in the inversion process. Numerical examples are conducted to verify the proposed inversion method. In the real data application, the observed deep reflection seismic data contain 106-shot profiles in the central part of the Lhasa Terrain, and the data coverage range is about 21km. In the result of FWI, the boundary between the Paleozoic strata (P2) and the Cenozoic strata (Qh) is very clear. Fault A is the boundary between Mesozoic strata (J3K1) and Paleozoic strata (D). The Paleozoic strata have a high velocity and significant uplift. Therefore, the FWI result can better characterize the lateral boundaries of strata in different ages than the tomography result. In the deep part, and the FWI result provides corrections to the interface morphology and more detailed structural information than the tomography result.