Power spectral densities and ambient noise cross-correlations at Long Beach

Chang, Jason P.; Ridder, Sjoerd de; Biondi, Biondo

doi:10.1190/segam2013-1412.1

Cited by 3 publications

(3 citation statements)

References 6 publications

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“…Because the array is located along the coast and in an urban environment, it is dominated by coastal energy at low frequencies (below 2 Hz) and by anthropogenic sources within the array at high frequencies (above 2 Hz). Studies have already demonstrated success at extracting surface waves below 4 Hz from Phase 1 (Lin et al, 2012(Lin et al, , 2013 and Phase 2 (Chang et al, 2013). In Phase 1, Lin et al (2012Lin et al ( , 2013 have also observed body waves when stacking over multiple virtual sources.…”

Section: Introductionmentioning

confidence: 93%

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High-frequency surface and body waves from ambient noise cross-correlations at Long Beach, CA

Chang¹,

Nakata²,

Clapp³

et al. 2014

SEG Technical Program Expanded Abstracts 2014

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The density and duration of the Long Beach, California passive seismic array makes it well-suited for applying ambient noise cross-correlation at high frequencies (3 Hz to 9 Hz). By correlating noise at these frequencies, both Rayleigh-wave and body-wave energy can be recovered. Here, we attempt to understand the origin of this energy. Beamforming reveals that Rayleigh-wave energy is generated by traffic noise, and it is particularly strong near Interstate 405. Virtual source gathers along a line of receivers perpendicular to the highway reinforces this observation. By summing over different virtual source-receiver azimuths, we find that body-wave energy arrives from north-northwest of the array. By looking at correlation results from various patches of virtual source-receiver pairs, we find that body-wave energy is strongest in the center of the array.

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Section: Introductionmentioning

confidence: 93%

“…To determine where the energy of these body waves is strongest, we sum correlations contained in patches throughout the array. Chang et al (2013) were able to recover Rayleigh waves up to 4 Hz at this site. From power spectral density maps, it appeared that anthropogenic sources dominated the noise field at these frequencies.…”

Section: Introductionmentioning

confidence: 94%

High-frequency surface and body waves from ambient noise cross-correlations at Long Beach, CA

Chang¹,

Nakata²,

Clapp³

et al. 2014

SEG Technical Program Expanded Abstracts 2014

Self Cite

View full text Add to dashboard Cite

show abstract

“…At these frequencies, multiple studies have shown that traffic noise dominates the ambient noise field. Power spectral density maps (Chang et al, 2013;Nakata et al, 2015) and beamforming of the ambient noise field (Chang et al, 2014) reveal Interstate 405 as the dominant source of seismic energy and local roads as the secondary source. We begin with an overview of our ambient noise processing procedure for harnessing this traffic noise.…”

Section: Introductionmentioning

confidence: 98%

Rayleigh-wave tomography using traffic noise at Long Beach, CA

Chang

Biondi

2015

SEG Technical Program Expanded Abstracts 2015

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Passive seismic arrays on land provide the opportunity to push the use of ambient noise cross-correlation techniques to frequencies well beyond the microseism band. Using data recorded by a dense array in Long Beach, California, we demonstrate that high-frequency (> 3 Hz) fundamental-and first-order-mode Rayleigh waves generated by traffic noise can be extracted from the ambient noise field and used for tomographic studies. Here, we show group velocity maps derived from travel times of the fundamental-mode Rayleigh waves at 3.00 Hz and 3.50 Hz. The velocity trends in our results correlate well with lithologies outlined in a geologic map of the survey region. As expected, less-consolidated materials display relatively low velocities, while more-consolidated materials display relatively high velocities.

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The coherency of ambient seismic noise recorded during land surveys and the resulting implications for the effectiveness of geophone arrays

2015

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The use of analog sensor arrays is often assumed to provide signal-to-ambient-noise improvements proportional to the square root of the number of sensors being summed. We determined via numerical modeling and field experiments that the improvements sought were significantly hindered once the ambient noise exhibited coherence over the array being summed. As a first step, a numerical model was developed to explore the optimal sensor spacing based on the average correlation coefficient between sensors. Field experiments were then carried out to measure ambient noise using closely spaced geophones at several sites in Perth, Western Australia. We show that the measured noise at six test sites was strongly coherent over distances of up to 10 m, with the level of coherency being inversely proportional to frequency. The resulting optimum geophone spacing under our field conditions was determined to be 7.5 m. These results offered further encouragement to reassess our use of analog arrays and to consider recording the output from individual sensors. In addition to the benefits from postacquisition noise suppression, this approach will enable increased trace density without degradation of the signal caused by strong coherent noise sources over acquisition spreads.

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Power spectral densities and ambient noise cross-correlations at Long Beach

Cited by 3 publications

References 6 publications

High-frequency surface and body waves from ambient noise cross-correlations at Long Beach, CA

High-frequency surface and body waves from ambient noise cross-correlations at Long Beach, CA

Rayleigh-wave tomography using traffic noise at Long Beach, CA

The coherency of ambient seismic noise recorded during land surveys and the resulting implications for the effectiveness of geophone arrays

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