Directionality of ambient noise on the Juan de Fuca plate: implications for source locations of the primary and secondary microseisms

Tian, Ye; Ritzwoller, M. H.

doi:10.1093/gji/ggv024

Cited by 65 publications

(56 citation statements)

References 41 publications

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“…1c), with the greatest signal energy generally occurring during the Northern Hemisphere winter from January to March. These variations are consistent with the expected mechanisms of secondary microseism noise generation by non-linear wave interaction in the north Atlantic, where a strong source region has been identified to the south of Greenland (Stehly et al 2006;Kedar et al 2008;Tian & Ritzwoller 2015). Despite these amplitude variations, the arrival times of the dominant peaks remain stationary in time.…”

Section: N O I S E C O R R E L At I O N I N T H E M I C Ro S E I S M supporting

confidence: 86%

Long-range correlations of microseism-band pressure fluctuations in the ocean

Ball

Godin

Evers

et al. 2017

The Journal of the Acoustical Society of America

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We investigate the spatial coherence of underwater infrasonic noise using a yearlong time series measured by hydrophones moored off Ascension Island. Qualitative agreement with observed cross-correlations is achieved using a simple range-dependent model, constrained by earlier, active tomographic studies in the area. In particular, the model correctly predicts the existence of two weakly dispersive normal modes in the microseism frequency range, with the group speed of one of the normal modes being smaller than the sound speed in water. The agreement justifies our interpretation of the peaks of the measured cross-correlation function of ambient noise as modal arrivals, with dispersion that is sensitive to crustal velocity structure. Our observations are consistent with Scholte to Moho head wave coupled propagation, with double mode conversion occurring due to the bathymetric variations between receivers. We thus demonstrate the feasibility of interrogating crustal properties using noise interferometry of moored hydrophone data at ranges in excess of 120 km.

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Section: N O I S E C O R R E L At I O N I N T H E M I C Ro S E I S M supporting

confidence: 86%

Long-range correlations of microseism-band pressure fluctuations in the ocean

Ball

Godin

Evers

et al. 2017

The Journal of the Acoustical Society of America

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“…Figure presents the group velocity (a and b, top) and the phase velocity (a and b, bottom) of Rayleigh wave normal modes. At these periods, i.e., between 3 and 10 s, the fundamental mode, the first and the second overtones show the presence of a minimum group velocity, called Airy phase [ Pekeris , ], which has been observed in oceanic environments by, e.g., Press and Ewing [], Press et al [], Ewing et al [], Oliver and Ewing [], Ritzwoller and Levshin [], Harmon et al [], and Tian and Ritzwoller []. The Airy phase occurs at some given frequency which depends on the ocean thickness.…”

Section: The Ocean‐continent Boundary Effectmentioning

confidence: 99%

“…In particular, it has been seen that the fundamental mode of Rayleigh waves is always present on the vertical component of ocean bottom noise records with periods between 3 and 10 s, whereas the first overtone appears only at short periods [ Harmon et al , ; Yao et al , ]. Several studies have also shown the presence of a slow phase having group velocity around 1 km/s [ Press and Ewing , ; Press et al , ; Ewing et al , ; Oliver and Ewing , ; Ritzwoller and Levshin , ; Harmon et al , ; Tian and Ritzwoller , ].…”

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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“…Previously developed localization methods for ambient sources include spectral analysis (e.g., Anthony et al, ; Bromirski, ; Bromirski & Duennebier, ), polarization analysis (e.g., Chevrot et al, ; Schimmel et al, ; Schulte‐Pelkum et al, ), cross correlation‐based imaging (e.g., Ermert et al, ; Stehly et al, ; Tian & Ritzwoller, ; Yang & Ritzwoller, ), beamforming (e.g., Behr et al, ; Gal et al, ; Gerstoft & Tanimoto, ; Juretzek & Hadziioannou, ; Kurrle & Widmer‐Schnidrig, ; Landès et al, ; Reading et al, ; Rhie & Romanowicz, ), migration of cross‐correlation signals (Brzak et al, ; Dales et al, ; Retailleau et al, ), grid searches for fitting particular observables (Gaudot et al, ; Rhie & Romanowicz, ; Shapiro et al, ), and inversion based on simplified plane‐wave models of noise cross correlations (Harmon et al, ; Lehujeur et al, ; Sadeghisorkhani et al, ; Yao & van der Hilst, ). Nishida and Fukao () inverted for the seasonal source of the Earth's hum using a model of cross correlations based on normal modes and a spherically symmetric Earth model.…”

Section: Introductionmentioning

confidence: 99%

Ambient Seismic Source Inversion in a Heterogeneous Earth: Theory and Application to the Earth's Hum

et al. 2017

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The sources of ambient seismic noise are extensively studied both to better understand their influence on ambient noise tomography and related techniques, and to infer constraints on their excitation mechanisms. Here we develop a gradient‐based inversion method to infer the space‐dependent and time‐varying source power spectral density of the Earth's hum from cross correlations of continuous seismic data. The precomputation of wavefields using spectral elements allows us to account for both finite‐frequency sensitivity and for three‐dimensional Earth structure. Although similar methods have been proposed previously, they have not yet been applied to data to the best of our knowledge. We apply this method to image the seasonally varying sources of Earth's hum during North and South Hemisphere winter. The resulting models suggest that hum sources are localized, persistent features that occur at Pacific coasts or shelves and in the North Atlantic during North Hemisphere winter, as well as South Pacific coasts and several distinct locations in the Southern Ocean in South Hemisphere winter. The contribution of pelagic sources from the central North Pacific cannot be constrained. Besides improving the accuracy of noise source locations through the incorporation of finite‐frequency effects and 3‐D Earth structure, this method may be used in future cross‐correlation waveform inversion studies to provide initial source models and source model updates.

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Directionality of ambient noise on the Juan de Fuca plate: implications for source locations of the primary and secondary microseisms

Cited by 65 publications

References 41 publications

Long-range correlations of microseism-band pressure fluctuations in the ocean

Long-range correlations of microseism-band pressure fluctuations in the ocean

On the shaping factors of the secondary microseismic wavefield

Ambient Seismic Source Inversion in a Heterogeneous Earth: Theory and Application to the Earth's Hum

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