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Harnessing high-performance computers and accurate numerical methods to better constrain physical properties of Earth's interior is becoming one of the most important research topics in structural and exploration seismology. We use spectral-element and adjoint methods to iteratively improve 3D subsurface images ranging from continental to exploration scales.

The spectral-element method, a high-order finite-element method with the advantage of a diagonal mass matrix, is used to accurately calculate three-component synthetic seismograms in a complex 3D Earth model. An adjoint method is used to numerically compute Frechet derivatives of a misfit function based on the interaction between the wavefield for a reference Earth model and a wavefield obtained by using time-reversed differences between data and synthetics at all receivers as simultaneous sources. In combination with …