Near-surface structure from ambient-noise tomography and horizontal-to-vertical spectral ratio beneath the Nankou-Sunhe fault

Urban geophysics ups the ante in the world of applied geophysics, which requires innovative thinking and seemingly off-the-wall approaches, if for no other reason than the settings. Ambient-noise-tomography (ANT) can play a pivotal role in yielding subsurfa2ce information in urban areas, which is capable of dealing with challenges related to these scenarios ( e.g., human activities and low signal-to-noise ratio). In this study, the ANT was conducted to investigate the near-surface shear-velocity structure in the surrounding area of the Baotu Spring Park in downtown Jinan, Shandong Province, China. Quiet clear Rayleigh waves have been obtained by the cross-correlation, which indicates that strong human activities, such as moving vehicles and municipal engineering constructions, can produce approximately isotropic distribution of noise sources for high-frequency signals. The direct surface-wave tomographic method with period-dependent ray-tracing was used to invert all surface-wave dispersion data in the period band 0.2-1.5 s simultaneously for 3D variations of shear-velocity (Vs) structure. Our results show a good correspondence to the geological features with thinner Quaternary sediments, the geological structural characteristic of the limestone surrounded by the igneous which has the highest velocity than that of the limestone in the study area, and several concealed faults of which specific location has been detected at depth. The results demonstrate that it is possible to successfully use ANT with high-frequency signal in an urban environment provided a detailed planning and execution is implemented.

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Void Hunting

10.18122/td.1832.boisestate ◽

2021 ◽

Author(s):

John B. Paustian

Keyword(s):

Surface Wave ◽

Ambient Noise ◽

Temporal Variations ◽

Ambient Noise Tomography ◽

Active Dissolution ◽

Near Surface ◽

Karst Environment ◽

Active Source ◽

Seismic Methods ◽

Spatio Temporal

Karst environments are characterized by voids, i.e. sinkholes and conduits of varying size that arise from the active dissolution of carbonate rock by acidic groundwater. These voids, whether air-, water-, or soil-filled, can be difficult to image using near-surface geophysical methods due to the limited investigation depths of most active-source methods. In addition, due to the significant effort it takes to collect active-source data, investigators are often unable to monitor spatio-temporal variations in the subsurface. The ability to detect, image, and monitor subsurface voids improves the understanding of processes that create and transform voids, a vitally important insight across a variety of scientifc disciplines and engineering applications, including hydrogeology, geotechnical engineering, planetary science and even issues of national security. Using a 54-element nodal array (1C and 3C sensors), I image the subsurface of the USF GeoPark with ambient noise surface wave tomography. I also use complementary active-source geophysical datasets (e.g. 2D ERT) collected at the GeoPark to constrain and/or validate the tomography results. I address two research questions with this study: (1) How do ambient seismic methods complement active-source near-surface methods? (2) Can ambient noise tomography resolve voids in the karst environment? In this thesis, I discuss my answers to these questions and present the current state of surface wave methods in the karst environment, including the feasibility for utilizing ambient noise methods to monitor spatio-temporal changes in sinkhole and conduit formation. In addition to the ability to use seismic methods for temporal monitoring, ambient noise provides lower frequencies than what are achievable with active-source seismic methods. Using frequencies from 5-28 Hz, ambient noise tomography is able to image deeper into the subsurface (up to 100 m at 5 Hz) than previous active-source seismic studies at the GeoPark field site. This study yields a more robust and simple method to image voids in covered karst environments and a long-term installation of ambient seismic nodes enables future investigations of spatio-temporal variations in void structures.

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Urban near-surface imaging from ambient noise tomography using dense seismic networks

IOP Conference Series Earth and Environmental Science ◽

10.1088/1755-1315/660/1/012058 ◽

2021 ◽

Vol 660 (1) ◽

pp. 012058

Author(s):

Changjiang Zhou ◽

Jianghai Xia ◽

Hongyu Zhang ◽

Jingyin Pang ◽

Ya Liu ◽

...

Keyword(s):

Ambient Noise ◽

Surface Imaging ◽

Ambient Noise Tomography ◽

Near Surface ◽

Seismic Networks

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Near-surface ambient noise tomography in the Baogutu copper deposit area

Journal of Geophysics and Engineering ◽

10.1088/1742-2132/13/6/868 ◽

2016 ◽

Vol 13 (6) ◽

pp. 868-874 ◽

Cited By ~ 1

Author(s):

Xin-xin Li ◽

Qing-chun Li

Keyword(s):

Ambient Noise ◽

Copper Deposit ◽

Ambient Noise Tomography ◽

Near Surface

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Seabed property estimation from ambient-noise recordings: Part 2 — Scholte-wave spectral-ratio inversion

Geophysics ◽

10.1190/1.2719062 ◽

2007 ◽

Vol 72 (4) ◽

pp. U47-U53 ◽

Cited By ~ 14

Author(s):

Everhard Muyzert

Keyword(s):

Ambient Noise ◽

Spectral Ratio ◽

Shear Velocity ◽

Velocity Model ◽

Surface Shear ◽

Data Set ◽

Recording Time ◽

Near Surface ◽

Scholte Waves ◽

Scholte Wave

Having knowledge of the near-surface shear-velocity model is useful for various seismic processing methods such as shear-wave static estimation, wavefield separation, and geohazard prediction. I present a new method to derive a 2D near-surface shear-velocity model from ambient-noise recordings made at the seafloor. The method relies on inverting horizontal- and vertical-amplitude spectra of Scholte waves propagating in the seafloor. I compare the commonly used horizontal-over-vertical spectral ratio with three alternative spectral-ratio definitions through modeling. The modeling shows that the vertical-over-total spectral ratio has some favorable properties for inversion. I describe a nonlinear inversion method for the vertical-to-total spectral ratio of the Scholte waves and apply it to an ambient-noise data set recorded by an ocean-bottom-cable (OBC) system. A 1D near-surface shear-velocity model is derived through a joint inversion of the spectral-ratio and phase-velocity data. A 2D shear-velocity model is obtained through a local inversion of the spectral ratios averaged over small groups of receivers and shows evidence for lateral heterogeneity. The newly developed method for deriving near-surface shear-velocity distribution by inverting the Scholte-wave spectral ratio measured from seabed noise provides great opportunities for estimating the shallow-seabed shear velocity in deep water. Another benefit of the method is that, with the OBC system, no additional hardware is needed; only additional recording time is required. In this case, half an hour is sufficient.

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