Simulations of seismic wave propagation in the North Island of New Zealand for tomographic inversion

Understanding crustal structure critically relies on seismic velocity models. In the North Island of New Zealand, three-dimensional (3D) velocity models have been previously developed, providing constraints on factors controlling the occurrence of a spectrum of fault slip behaviours in the Hikurangi subduction zone. For example, a recent study by Wallace et al. (2017) showed that a sedimentary wedge in subduction zones causes the amplification of ground motion, inducing large dynamic stress perturbations on the plate inference and promoting triggering of fault slip. However, the accuracy and resolution of these seismic velocity models have not been rigorously quantified. In this study, we have developed a simulation framework that accurately computes synthetic seismograms for the latest 3D velocity model (Eberhart-Phillips and Bannister, 2015) for the North Island of New Zealand. We demonstrate the accuracy of the 3D velocity model by comparing 3D synthetics with observed waveforms for well-recorded local earthquakes originating in the crust and underlying subducting slab. Waveform misfits between data and synthetics provide a basis for a tomographic inversion. We report our current effort towards an iterative tomographic inversion for the North Island of New Zealand using adjoint methods.