Resolving subsurface velocities with FWI

摘要

Full-waveform inversion is becoming a practical and important technology for determining seismic velocities. Full-waveform inversion (FWI) was introduced to the field of exploration seismology in the early '80s by Albert Tarantola. However, it is only recently that FWI has entered the mainstream of seismic imaging and become the preferred tool for estimating complex velocity distributions. In his groundbreaking work, Tarantola laid out the theoretical foundation for FWI, and now, almost 30 years later, little of this has changed except for what one could call a revolution around the practical implementation aspects of the technology. The key idea behind FWI is a data-space matching, where the objective is to match synthetic/modeled data to the data recorded in the field. As FWI inherently is a nonlinear problem, the solution is pursued in an iterative manner, where the data misfit or data residual is added (in a smart way) to the starting velocity model that was used to create the synthetics, creating an updated velocity model that yields synthetic data that more closely match the field recordings. This data-driven approach holds the promise of being a highly automated way of estimating velocities where, given the right data, one could directly recover an estimate of the velocity distribution in the subsurface. This velocity model could then be used to create accurate images of the subsurface, even in regions with very complex geology and velocity distributions that have normally challenged seismic imaging technology.