How moderate sea states can generate loud seismic noise in the deep ocean

Obrebski, Mathias; Ardhuin, Fabrice; Stutzmann, É.; Schimmel, Martin

doi:10.1029/2012gl051896

Cited by 61 publications

(69 citation statements)

References 26 publications

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“…Because swells propagate over long distances, they are likely to encounter other swells or wind seas away from the usual storm tracks (see, for example, the event described in Obrebski et al . []). The sources generated under these specific conditions are expected to be weaker (because interacting swells have been attenuated since they emanated from the storm) and more widely distributed and could be detected by lowering our selection threshold (horizontal line in Figure ).…”

Section: Discussionmentioning

confidence: 99%

Detection of microseismic compressional (P) body waves aided by numerical modeling of oceanic noise sources

et al. 2013

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[1] Among the different types of waves embedded in seismic noise, body waves present appealing properties but are still challenging to extract. Here we first validate recent improvements in numerical modeling of microseismic compressional (P) body waves and then show how this tool allows fast detection and location of their sources. We compute sources at~0.2 Hz within typical P teleseismic distances (30-90°) from the Southern California Seismic Network and analyze the most significant discrete sources. The locations and relative strengths of the computed sources are validated by the good agreement with beam-forming analysis. These 54 noise sources exhibit a highly heterogeneous distribution, and cluster along the usual storm tracks in the Pacific and Atlantic oceans. They are mostly induced in the open ocean, at or near water depths of 2800 and 5600 km, most likely within storms or where ocean waves propagating as swell meet another swell or wind sea. We then emphasize two particularly strong storms to describe how they generate noise sources in their wake. We also use these two specific noise bursts to illustrate the differences between microseismic body and surface waves in terms of source distribution and resulting recordable ground motion. The different patterns between body and surface waves result from distinctive amplification of ocean wave-induced pressure perturbation and different seismic attenuation. Our study demonstrates the potential of numerical modeling to provide fast and accurate constraints on where and when to expect microseismic body waves, with implications for seismic imaging and climate studies.Citation: Obrebski, M., F. Ardhuin, E. Stutzmann, and M. Schimmel (2013), Detection of microseismic compressional (P) body waves aided by numerical modeling of oceanic noise sources,

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Section: Discussionmentioning

confidence: 99%

Detection of microseismic compressional (P) body waves aided by numerical modeling of oceanic noise sources

et al. 2013

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“…2,3 At large depths, noise has been associated with seismic pseudo-Rayleigh waves that propagate over thousands of kilometers, 3,4 from oceans to land. The term "pseudo-Rayleigh" is also used for the same modes generated by earthquakes, and it emphasizes the effect of the water layer in which the motion is a superposition of obliquely propagating sound waves.…”

Section: Introductionmentioning

confidence: 99%

A numerical model for ocean ultra-low frequency noise: Wave-generated acoustic-gravity and Rayleigh modes

Ardhuin

Lavanant

Obrebski

et al. 2013

The Journal of the Acoustical Society of America

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The generation of ultra-low frequency acoustic noise (0.1 to 1 Hz) by the nonlinear interaction of ocean surface gravity waves is well established. More controversial are the quantitative theories that attempt to predict the recorded noise levels and their variability. Here a single theoretical framework is used to predict the noise level associated with propagating pseudo-Rayleigh modes and evanescent acoustic-gravity modes. The latter are dominant only within 200 m from the sea surface, in shallow or deep water. At depths larger than 500 m, the comparison of a numerical noise model with hydrophone records from two open-ocean sites near Hawaii and the Kerguelen islands reveal: (a) Deep ocean acoustic noise at frequencies 0.1 to 1 Hz is consistent with the Rayleigh wave theory, in which the presence of the ocean bottom amplifies the noise by 10 to 20 dB; (b) in agreement with previous results, the local maxima in the noise spectrum support the theoretical prediction for the vertical structure of acoustic modes; and (c) noise level and variability are well predicted for frequencies up to 0.4 Hz. Above 0.6 Hz, the model results are less accurate, probably due to the poor estimation of the directional properties of wind-waves with frequencies higher than 0.3 Hz.

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“…The amplitude of land‐recorded seismic noise in relation with the source location and efficiency to transmit seismic energy from the ocean to the continent is still under debate. Evidence of dominant offshore noise sources located in deep ocean environments has been documented by Webb and Constable [], Cessaro [], Stehly et al [], Kedar et al [], and Obrebski et al [] for noise Rayleigh waves and by Gerstoft et al [], Koper and de Foy [], Koper et al [, ], Zhang et al [], Obrebski et al [], and Gualtieri et al [] for noise body waves. Evidence of noise sources associated with coastal reflection in shallow water has been documented by Darbyshire [], Bromirski et al [], Bromirski [], Bromirski and Duennebier [], Bromirski et al [], Essen et al [], Schulte‐Pelkum et al [], Gerstoft and Tanimoto [], Tanimoto [], Yang and Ritzwoller [], and Ardhuin et al [].…”

Section: Introductionmentioning

confidence: 99%

On the shaping factors of the secondary microseismic wavefield

et al. 2015

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Seismic noise in the period band 3–10 s is known as secondary microseism, and it is generated at the ocean surface by the interaction of ocean gravity waves coming from nearly opposite directions. In this paper, we investigate the seismic content of the wavefield generated by a source at the ocean surface and three of the major wavefield shaping factors using the 2‐D spectral element method: the ocean‐continent boundary, the source site effect, and the thickness of seafloor sediments. The seismic wavefield recorded on the vertical component seismograms below the seafloor is mainly composed of the fundamental mode and the first overtone of Rayleigh waves. A mode conversion from the first overtone to the fundamental mode of Rayleigh waves occurs at the ocean‐continent boundary. The presence of a continental shelf at the ocean‐continent boundary produces a negligible effect on land‐recorded seismograms, whereas the source site effect, i.e., the source location with respect to the local ocean depth and sediment thickness, plays the major role. A source in shallow water mostly enhances the fundamental mode of Rayleigh waves, whereas a source in deep water mainly enhances the first overtone of Rayleigh waves. Land‐recorded long‐period signals (T > 6 s) are mostly due to deep water sources, whereas land‐recorded short‐period signals (T < 6 s) are due to sources in relatively shallow water, located close to the shelf break. Seafloor sediments around the source region trap seismic waves reducing the amplitude of land‐recorded signals, especially at long periods (T > 6 s).

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How moderate sea states can generate loud seismic noise in the deep ocean

Cited by 61 publications

References 26 publications

Detection of microseismic compressional (P) body waves aided by numerical modeling of oceanic noise sources

Detection of microseismic compressional (P) body waves aided by numerical modeling of oceanic noise sources

A numerical model for ocean ultra-low frequency noise: Wave-generated acoustic-gravity and Rayleigh modes

On the shaping factors of the secondary microseismic wavefield

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