Full-waveform inversion of surface waves can provide high-resolution S-wave velocity (Vs) of the shallow subsurface and is becoming a popular shallowseismic method. We propose a misfit function based on instantaneous-phase coherency, which can measure the amplitude-unbiased coherency between measured and synthetic data. The instantaneous-phase coherency was once the key component that was used in the phase-weight stacking technology to enhance the weak but coherent signals. Using synthetic data, we show that our full-waveform inversion approach based on the proposed misfit function is robust in reconstructing subsurface anomalies from data contaminated by random noise. We also show that our misfit function is robust against the errors in the estimated source wavelets. We then choose to use published field data acquired at an archaeological site as a benchmark dataset to test the performance of our full-waveform inversion in a real environment. Subsurface structures identified in our inversion results are verified by an independent archaeological excavation, while the results from conventional full-waveform inversion are dominated by artefacts. The results of synthetic tests and field data experiments demonstrate the robustness of our full-waveform inversion approach in reconstructing the shallow subsurface structure from field data, where amplitude information of recorded wavefield may not be correctly recorded.

Seismoelectric coupling in an electric isotropic and elastic anisotropic medium is developed using a primary-secondary formulation. The anisotropy is of vertical transverse isotropic type and concerns only the poroelastic parameters. Based on our finite difference time domain algorithm, we solve the seismoelectric response to an explosive source. The seismic wavefields are computed as the primary field. The electric field is then obtained as a secondary field by solving the Poisson equation for the electric potential. To test our numerical algorithm, we compared our seismoelectric numerical results with analytical results obtained from Pride's equation. The comparison shows that the numerical solution gives a good approximation to the analytical solution. We then simulate the seismoelectric wavefields in different models. Simulated results show that four types of seismic waves are generated in anisotropic poroelastic medium. These are the fast and slow longitudinal waves and two separable transverse waves. All of these seismic waves generate coseismic electric fields in a homogenous anisotropic poroelastic medium. The tortuosity has an effect on the propagation of the slow longitudinal wave. The snapshot of the slow longitudinal wave has an oval shape when the tortuosity is anisotropic, whereas it has a circular shape when the tortuosity is isotropic. In terms of the Thomsen parameters, the radiation anisotropy of the fast longitudinal wave is more sensitive to the value of ε, while the radiation anisotropy of the transverse wave is more sensitive to the value of δ.