First-arrival traveltime inversion with embedded boundary method for irregular topography

Abstract

The first-arrival traveltime tomography (FATT) is an inversion method which represents shallow velocities so that it is widely used to identify subsurface images in oil and gas industry as well as civil engineering and geotechnical industries. The provided shallow velocity can be generally utilized for static correction which is necessary for land seismic data processing. Land data, which involve elevation variations, require to consider irregular topography carefully when performing the wave-equation-based traveltime tomography. In this study, in order to express the irregular topography, embedded boundary method (EBM) is incorporated into our traveltime calculation method which is based on damped wavefields from wave equation modeling. EBM can precisely construct irregular surface of numerical models on regular mesh by exploiting the mirror imaging method and Lagrangian interpolation. Through numerical examples and field data, the developed techniques are demonstrated. First of all, using a homogeneous velocity having slanted surface, the EBM-based traveltime calculation method is validated. The results show that our EBM-based traveltime calculation is no longer affected by the staircase approximation. Additionally, using field data which are obtained from mountainous area, the EBM-based FATT is carried out to estimate the shallow velocity. The inverted velocity is then used to apply static correction to the field data in a simple manner. The processing results show that the continuities of seismic events are improved which can claim the accurateness of our FATT method.