SANS: Publicly Available Daily Multi‐Scale Seismic Ambient Noise Source Maps

Igel, Jonas; Bowden, D. C.; Fichtner, Andreas

doi:10.1029/2022jb025114

Cited by 8 publications

(5 citation statements)

References 74 publications

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“…The direction to the noise sources can be estimated from the properties of the energy flux of the wavefield, which is typically determined by applying beamforming or frequency‐wavenumber array analysis techniques to far‐field observations (Nishida, 2017, and references within). However, even though information about the background illumination can help mitigate the bias on the phase velocity estimation (Igel et al., 2023), results of these methods are not routinely used for quality assessment in ambient noise tomography applications. The USArray focal spot shapes (Figure 3b) are influenced by anisotropic surface wave incidence (Section 2.3).…”

Section: Resultsmentioning

confidence: 99%

Long Period Rayleigh Wave Focal Spot Imaging Applied to USArray Data

Tsarsitalidou,

Hillers,

Giammarinaro

et al. 2024

JGR Solid Earth

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We demonstrate the effectiveness of seismic dense array surface wave focal spot imaging using USArray data from the western‐central United States. We study dispersion in the 60–310 s period range and assess the image quality of fundamental mode Rayleigh wave phase velocity maps. We apply isotropic spatial autocorrelation models to the time domain zero lag noise correlation wavefield data at distances of about one wavelength. Local estimates of the phase velocity, its uncertainty, and the regression quality imply overall better ZZ relative to ZR or RZ results. The extension of the depth resolution compared to passive surface wave tomography is demonstrated by the inversion of three clustered dispersion curves from different tectonic units. We observe anisotropic surface wave energy flux and the influence of body wave energy, but sensitivity tests at 60 s targeting the data range, correlation component, and processing choices show that the ZZ focal spots yield consistent high‐quality images compared to regional tomography results in the 60–150 s period range. In contrast, at 200–300 s the comparatively small scales of the imaged structures and the imperfect agreement with low‐resolution global tomography results highlight the persistent challenge to reconcile imaging results based on different data sources, theories, and techniques. Our study shows that surface wave focal spot imaging is an accurate, robust, local imaging approach. Better control over clean autocorrelation fields can further improve applications of this seismic imaging tool for increased resolution of the elastic structure below dense seismic arrays.

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Section: Resultsmentioning

confidence: 99%

Long Period Rayleigh Wave Focal Spot Imaging Applied to USArray Data

Tsarsitalidou,

Hillers,

Giammarinaro

et al. 2024

JGR Solid Earth

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“…Therefore, it is crucial to verify that the observed waveform changes arise from subsurface physical property changes, rather than being linked to variations in the ambient noise sources. We employ the beamforming method (Bowden et al., 2021; Bucker, 1976; Igel et al., 2023) to map the seafloor ambient noise source on an hourly basis. Figure 4 shows the OBN geometry, array responses and beamforming results for spiral‐arm and rectangular layouts, respectively.…”

Section: Methods and Resultsmentioning

confidence: 99%

Space‐Time Monitoring of Seafloor Velocity Changes Using Seismic Ambient Noise

Guo,

Saygin,

Kennett

2024

JGR Solid Earth

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We use seismic ambient noise recorded by dense ocean bottom nodes (OBNs) in the Gorgon gas field, Western Australia, to compute time‐lapse seafloor models of shear‐wave velocity. The extracted hourly cross‐correlation (CC) functions in the frequency band 0.1–1 Hz contain mainly Scholte waves with very high signal‐to‐noise ratio. We observe temporal velocity variations (dv/v) at the order of 0.1% with a peak velocity change of 0.8% averaged from all station pairs, from the conventional time‐lapse analysis with the assumption of a spatially homogeneous dv/v. With a high‐resolution reference (baseline) model from full waveform inversion of Scholte waves, we present an elastic wave equation based double‐difference inversion (EW‐DD) method, using arrival time differences between the reference and time‐lapsed Scholte waves, for mapping temporally varying dv/v in the heterogeneous subsurface. The time‐lapse velocity models reveal increasing/decreasing patterns of shear‐wave velocity in agreement with those from the conventional analysis. The velocity variation exhibits a ∼24‐hr cycling pattern, which appears to be inversely correlated with the diurnal variations in sea level height, possibly associated with dilatant effects for porous, low‐velocity shallow seafloor and rising pore pressure with higher sea level. This study demonstrates the feasibility of using dense passive seismic surveys and wave‐equation time‐lapse inversion for quantitative monitoring of subsurface property changes in the horizontal and depth domain.

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“…Seismic data are both freely distributed by as well as being telemetered to global seismological data centers for earthquake monitoring, tsunami warning, and other rapid-response missions. Microseism metrics and modeling can therefore be jointly interpreted with other data sources either retrospectively or in near-real time [55].…”

Section: Discussionmentioning

confidence: 99%

Increasing near-coastal ocean wave energy observed in Earth’s seismic wavefield since the late 1980

Aster

Ringler

Anthony

et al. 2023

Preprint

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Earth’s seismic wavefield is continuously excited by forces on the seafloor arising from ocean gravity waves. The resulting microseism signal is detected worldwide by seismographic networks, even in the deep interiors of the continents, and its spatially and temporally variations reflect global ocean wave conditions. The primary microseism signal between 20 – 14 s period is principally composed of seismic Rayleigh waves that represent the spatiotemporal integrated seismic radiation excited across near coastal bathymetry. We analyze primary microseism vertical-component amplitudes, which are insensitive to Rayleigh wave propagation direction, through late 2022 using continuous seismic data recorded by globally distributed seismographs with operational intervals exceeding 20 years and beginning with the advent of modern continuous digital broadband recording in the late 1980s. Widespread increasing median amplitudes are apparent at the majority of global stations even prior to removing non-seismic instrumental and large earthquake signals and subtraction of the stationary component of the annual signal. Increasing primary microseism amplitudes and energies at 3σ significance occur for 41 of 52 stations. Significant decreasing trends for stations are geographically restricted to the northern and western Pacific region and to two sites in the southern United States. Amplitude and energy changes show broad proportionality, with the greatest absolute increases occurring at stations with historically high microseism levels. The most rapidly proportionately intensifying energy occurs at eastern North American and European sites that are principally sensitive to wave energy in the North Atlantic, and which show median average seismic energy increases over the past three decades of 0.7 – 0.8% per year relative to long-term median values. median values. The most rapidly intensifying primary microseism levels on an absolute basis are observed for the Antarctic Peninsula with an annualized vertical seismic acceleration, velocity, and energy trends (3σ uncertainties) of 0.037 ± 0.008 nm/s2/yr (0.36 ± 0.08 %/yr), 0.093 ± 0.02 nm/s/yr (0.35 ± 0.08 %/yr), and 4.16 ± 1.07 (nm/s)2 (0.58 ± 0.15 %/yr), respectively. Average inferred wave energy increase from seismic energy metrics across analyzed stations is 0.27±0.03 %/yr for the entire data period and 0.35±0.04 %/yr for the era beginning on January 1 2000.

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SANS: Publicly Available Daily Multi‐Scale Seismic Ambient Noise Source Maps

Abstract: Seismic ambient noise sources have been studied thoroughly over the last few decades with studies and theories about the noise source locations and mechanisms as early as the 19th century (

Cited by 8 publications

References 74 publications

Long Period Rayleigh Wave Focal Spot Imaging Applied to USArray Data

Long Period Rayleigh Wave Focal Spot Imaging Applied to USArray Data

Space‐Time Monitoring of Seafloor Velocity Changes Using Seismic Ambient Noise

Increasing near-coastal ocean wave energy observed in Earth’s seismic wavefield since the late 1980

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