scholarly journals Directionality of ambient noise in the Mississippi embayment

2020 ◽  
Vol 223 (2) ◽  
pp. 1100-1117
Author(s):  
Chunyu Liu ◽  
Khurram Aslam ◽  
Charles A Langston
Keyword(s):  
Deep Water ◽  
Ambient Noise ◽  
Broad Band ◽  
Power Spectra ◽  
Azimuthal Distribution ◽  
Recording Time ◽  
Mississippi Embayment ◽  
Rayleigh And Love Waves ◽  
Near Shore ◽  
Hemisphere Winter

SUMMARY Cross-correlations of ambient seismic noise from 277 broad-band stations within the Mississippi embayment (ME) with at least 1 month of recording time between 1990 and 2018 are used to estimate source locations of primary and secondary microseisms. We investigate source locations by analysing the azimuthal distribution of the signal-to-noise ratios (SNRs) and positive/negative amplitude differences. We use 84 stations with 1 yr of continuous recordings to explore seasonal variations of SNRs and amplitude differences. We also investigate the seasonal ambient noise ground motions using 2-D frequency–wavenumber (FK) analysis of a 50-station array. We observe that: (1) two major azimuths can be identified in the azimuthal distribution of SNRs and amplitude differences. We also observe two minor azimuths in the seasonal variation of SNRs, amplitude differences and 2-D FK power spectra. Monthly 2-D FK power spectra reveal that two energy sources are active in the Northern Hemisphere winter and two relatively weak sources are active in summer. (2) Backprojection suggests that primary microseisms originate along the coasts of Australia or New Zealand, Canada and Alaska, Newfoundland or Greenland and South America. (3) Secondary microseisms are generated in the deep water of the northern and southern Pacific Ocean, along the coasts of Canada and Alaska associated with near-shore reflections and in the deep water of south of Greenland. (4) Weak energy is observed in the third quadrant of the azimuthal distribution of amplitude differences of sedimentary Rayleigh and Love waves in the period band of 1–5 s and correlates with the direction of widening of the basin.

scholarly journals Multifrequency inversion of global ambient seismic sources

2021 ◽  
Vol 225 (3) ◽  
pp. 1616-1623
Author(s):  
L A Ermert ◽  
K Sager ◽  
T Nissen-Meyer ◽  
A Fichtner
Keyword(s):  
Southern Hemisphere ◽  
Ambient Noise ◽  
Source Region ◽  
Broad Band ◽  
Winter Season ◽  
Deep Ocean ◽  
Source Distribution ◽  
Source Inversion ◽  
Frequency Dependent ◽  
Hemisphere Winter

SUMMARY We develop and apply a method to constrain the space- and frequency-dependent location of ambient noise sources. This is based on ambient noise cross-correlation inversion using numerical wavefield simulations, which honour 3-D crustal and mantle structure, ocean loading and finite-frequency effects. In the frequency range from 3 to 20 mHz, our results constrain the global source distribution of the Earth’s hum, averaged over the Southern Hemisphere winter season of 9 yr. During Southern Hemisphere winter, the dominant sources are largely confined to the Southern Hemisphere, the most prominent exception being the Izu-Bonin-Mariana arc, which is the most active source region between 12 and 20 mHz. Generally, strong hum sources seem to be associated with either coastlines or bathymetric highs. In contrast, deep ocean basins are devoid of hum sources. While being based on the relatively small number of STS-1 broad-band stations that have been recording continuously from 2004 to 2013, our results demonstrate the practical feasibility of a frequency-dependent noise source inversion that accounts for the complexities of 3-D wave propagation. It may thereby improve full-waveform ambient noise inversions and our understanding of the physics of noise generation.

Spectrum Analysis of Deep Water Ambient Noise in the West Pacific

2021 ◽  
Author(s):  
Jiahua Zhu ◽  
Wei Guo ◽  
Bingbing Zhang ◽  
Yanxin Ma ◽  
Yangyang Chen ◽  
...  
Keyword(s):  
Deep Water ◽  
Spectrum Analysis ◽  
Ambient Noise ◽  
The West ◽  
West Pacific

Passive acoustic thermometry of the deep water sound channel using ambient noise

2013 ◽  
Vol 134 (5) ◽  
pp. 3983-3983
Author(s):  
Katherine F. Woolfe ◽  
Shane Lani ◽  
Karim G. Sabra
Keyword(s):  
Deep Water ◽  
Ambient Noise ◽  
Sound Channel ◽  
Acoustic Thermometry ◽  
Passive Acoustic

scholarly journals Ambient noise tomography of the southern sector of the Cantabrian Mountains, NW Spain

2019 ◽  
Vol 219 (1) ◽  
pp. 479-495 ◽  
Author(s):  
Jorge Acevedo ◽  
Gabriela Fernández-Viejo ◽  
Sergio Llana-Fúnez ◽  
Carlos López-Fernández ◽  
Javier Olona
Keyword(s):  
Ambient Noise ◽  
Broad Band ◽  
Shear Zones ◽  
Seismic Velocities ◽  
S Wave ◽  
Ambient Noise Tomography ◽  
Cantabrian Mountains ◽  
Nw Spain ◽  
Time Frequency ◽  
Short Period

SUMMARY This study presents the first detailed analysis of ambient noise tomography in an area of the continental upper crust in the Cantabrian Mountains (NW Spain), where a confluence of crustal scale faults occurs at depth. Ambient noise data from two different seismic networks have been analysed. In one side, a 10-short-period station network was set recording continuously for 19 months. A second set of data from 13 broad-band stations was used to extend at depth the models. The phase cross-correlation processing technique was used to compute in total more than 34 000 cross-correlations from 123 station pairs. The empirical Green's functions were obtained by applying the time–frequency, phase-weighted stacking methodology and provided the emergence of Rayleigh waves. After measuring group velocities, Rayleigh-wave group velocity tomographic maps were computed at different periods and then they were inverted in order to calculate S-wave velocities as a function of depth, reaching the first 12 km of the crust. The results show that shallow velocity patterns are dominated by geological features that can be observed at the surface, particularly bedding and/or lithology and fracturing associated with faults. In contrast, velocity patterns below 4 km depth seem to be segmented by large structures, which show a velocity reduction along fault zones. The best example is the visualization in the tomography of the frontal thrust of the Cantabrian Mountains at depth, which places higher velocity Palaeozoic rocks over Cenozoic sediments of the foreland Duero basin. One of the major findings in the tomographic images is the reduction of seismic velocities above the area in the crust where one seismicity cluster is nucleated within the otherwise quiet seismic area of the range. The noise tomography reveals itself as a valuable technique to identify shear zones associated with crustal scale fractures and hence, lower strain areas favourable to seismicity.

Modeling of Seafloor Soft Marine Sediments and Spectral Characteristics of Earthquakes Recorded on the Gulf of Mexico

2005 ◽  
Vol 127 (1) ◽  
pp. 59-67
Author(s):  
Carlos I. Huerta-Lopez ◽  
Kenneth H. Stokoe ◽  
Jay Pulliam ◽  
Celestino Valle-Molina ◽  
Jose´ M. Roe¨sset
Keyword(s):  
Gulf Of Mexico ◽  
Marine Sediments ◽  
Deep Water ◽  
Ambient Noise ◽  
Transfer Functions ◽  
Spectral Characteristics ◽  
Dynamic Loads ◽  
Experimental Site ◽  
Local Site Effect ◽  
Sediment Properties

In situ evaluation of the response of seafloor sediments to passive dynamic loads, as well as spectral analyses of earthquakes are presented in this investigation. The overall goal of this work was to develop a cost-effective method of characterizing offshore geotechnical sites in deep water. The generic approach was to place an ocean bottom seismograph on the seafloor and record ambient noise and distant earthquakes over periods of a month or more. Horizontal-to-vertical (H/V) spectral ratios are used to characterize the local sediment response in terms of the distribution of ground motions with their respective resonant frequencies. Both ambient noise and distant earthquakes are used as generators of passive dynamic loads. One-dimensional (1D) wave propagation modeling using the stiffness matrix method is used to estimate sediment properties (mainly shear stiffness, density, and material damping) and theoretical amplification factors of the shallow sediment layers. The objectives in this study were fourfold: First, to characterize the spectral characteristics of earthquake signals recorded in the seafloor at an experimental site in the Gulf of Mexico (GOM); second, to characterize the local site effect produced by shallow marine sediments at the GOM experimental site; third, to characterize the site in terms of its physical properties (layering and sediment properties); and fourth, to estimate the transfer functions of the top 50 m (164 ft) of soil and of each layer in the discrete soil model. The resulting sediment properties fall well within the expected range, indicating the potential of the proposed exploration approach for characterizing deep-water sites.

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