Full waveform inversion

Summary

Full waveform inversion is seismic tomography that fits entire recorded seismograms, not only picked arrival times. It simulates the waves in a trial Earth model by solving the wave equation and measures the misfit to the data. It then updates the model by local optimisation, with gradients from the adjoint state method. Since it uses amplitudes and phases of all arrivals, it can resolve structures down to about half a wavelength, much finer than travel-time tomography. Its main difficulty is that the misfit has many local minima, so it needs a good starting model and low frequencies.