In contrast, secondary microseisms derive from second-order pressure variations, resulting from the interaction of opposing ocean wave fronts 5, leading to vertical pressurization of the ocean floor in arbitrarily deep water. Generated in the ocean, primary microseisms originate from the direct action of propagating ocean gravity waves in shallow water.
#DEEP OCEAN WAVES WINDOWS#
There are two energetic spectral windows in the microseism wavefield, the primary (dominant periods 10–20 s) and secondary (dominant periods 3–10 s). Hence, they yield rich spatio-temporal information about ocean-land coupling in deep water.Ī better understanding of ocean generated seismic noise sources and associated wavefields is crucial for a variety of applications from seismic imagery 1 to subsurface monitoring 2 in addition to ocean wave climate and storm activity studies 3, 4. We conclude that, in contrast to Rayleigh waves, microseism Love waves observed on land do not directly relate to the ocean wave climate but are significantly modulated by continental margin morphologies, with a first order effect from sedimentary basins. We show that while Rayleigh to Love wave conversions occur along the microseism path, Love waves predominantly originate from steep subsurface geological interfaces and bathymetry, directly below the ocean source that couples to the solid Earth. Here, using terrestrial seismic arrays and 3D synthetic acoustic-elastic simulations combined with ocean wave hindcast data, we demonstrate that, observed from land, our general understanding of Rayleigh and Love wave microseism sources is significantly impacted by 3D propagation path effects.
While the origin of associated Rayleigh waves is well understood, there is currently no quantified explanation for the existence of Love waves in the most energetic region of the microseism spectrum (3–10 s). Wind driven ocean wave-wave interactions produce continuous Earth vibrations at the seafloor called secondary microseisms.
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