Ocean storms have long been known to generate seismic signals (microseisms) that are present even in areas where earthquakes rarely occur. When observed on a seismogram, the ocean storm signal is visible as a continuous oscillation of the solid Earth, and techniques that average over time are usually applied to extract information about the nature of the signals. We have developed a seismic array technique that does not require averaging over time and hence allows us to view the seismic wavefield as an instantaneous snapshot similar to a photograph.
When applied to the seismic wavefield, our method allows us to study the underlying nature of the ocean-generated seismic wavefield in unprecedented detail, and we find that seismic energy reaches the array in pulses rather than a continuous stream. We found that this was a direct result of the spatial extended generation region of microseisms, where the resulting wavefield forms pulses due to the superposition principle. The pulse-like nature can be used to retrieve relative travel times which yield information on the Earth’s structure. Computational work for this research was done in 2017 under ARC DP150101005. This grant was used specifically to assess the changes in wave climate and risk management to coastal communities, and will terminate in 2018.