Are deep‐ocean‐generated surface‐wave microseisms observed on land?

Abstract

[1] Recent studies attribute land double-frequency (DF) microseism observations to deep water generation. Here we show that near-coastal generation is generally the dominant source region. This determination is based on observations at land and ocean seismic stations, buoys, gravity-wave hindcasts, and on beamforming results from continental seismic arrays. Interactions between opposing ocean wave components generate a pressure excitation pulse at twice the ocean wave frequency that excites pseudo-Rayleigh (pRg) wave DF microseisms. pRg generated in shallow coastal waters have most of their energy in the solid Earth ("elastic" pRg) and are observed by land-based and seafloor seismometers as DF microseisms. pRg generated in the deep ocean have most of their energy in the ocean ("acoustic" pRg) and are continuously observed on the ocean bottom, but acoustic pRg does not efficiently transition onto continents. High-amplitude DF signals over the [0.2, 0.3] Hz band observed on the deep seafloor are uncorrelated with continental observations and are not clearly detectable at individual continental stations or by land seismic-array beamforming. Below 0.2 Hz, modeling and some observations suggest that some deep water-generated elastic pRg energy can reach continental stations, providing that losses from scattering and transition across the continental-shelf boundary to the shore are not substantial. However, most observations indicate that generally little deep-ocean-generated DF microseism energy reaches continental stations. Effectively, DF land observations are dominated by near-coastal wave activity.Citation: Bromirski, P. D., R. A. Stephen, and P. Gerstoft (2013), Are deep-ocean-generated surface-wave microseisms observed on land?,

Seafloor Seismic Noise at Central Eastern Mediterranean Sites

“…Observed microseismic noise has been explained by a physical process based on a nonlinear wave-wave interaction mechanism (Longuet-Higgins, 1950;Hasselmann, 1963). Several studies tried to locate the noise sources at sea (e.g., Bromirski and Duennebier, 2002;Bromirski et al, 2005Bromirski et al, , 2013Tanimoto, 2007), but only recently a wave-wave interaction model has been applied to predict the amplitude of microseismic noise and compare it with the ones observed by on-land seismometers (Kedar et al, 2008;Ardhuin et al, 2011). In addition to global sources of noise, such as long-wavelength ocean waves that also affect the remotest land sites, there are other more local-and/or site-dependent sources that determine the signal-to-noise level, therefore limiting the possibility to efficiently detect waveforms from seismic events.…”

Observation of continuous microseismic P waves in Asia

“…Most DF microseisms observed on land are generated in coastal regions by ocean wave activity and propagate into the continent primarily as Rayleigh waves [ Haubrich and McCamy , ; Cessaro , ; Friedrich et al , ; Schimmel et al , ; Bromirski et al , ]. However, it has also been reported that DF microseisms can be generated by distant mid‐ocean storms and propagate as P waves [ Haubrich and McCamy , ; Lacoss et al , ; Vinnik , ; Gerstoft et al , ; Koper et al , ; Sheen , ] and even as P P and P K P phases [ Gerstoft et al , ; Koper and de Foy , ; Koper et al , ; Landes et al , ].…”

Sources of secondary microseisms in the Indian Ocean

“…SM noise sources have been located in near-coastal shallow waters (e.g. Bromirski et al 2013), related to coastal swell reflections interacting with the incident swell (e.g. Bromirski & Duennebier 2002) and also in deep waters (e.g.…”