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Lingli Gao

Bio: Lingli Gao is an academic researcher from Karlsruhe Institute of Technology. The author has contributed to research in topics: Surface wave & Rayleigh wave. The author has an hindex of 9, co-authored 28 publications receiving 270 citations. Previous affiliations of Lingli Gao include Zhejiang University & China University of Geosciences (Wuhan).

Papers
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Journal ArticleDOI
TL;DR: In this article, a Love-wave waveform inversion was used to estimate near-surface S-wave velocity of earth models, which can be applied to any kind of earth model.
Abstract: High-frequency surface-wave techniques are widely used to estimate S-wave velocity of near-surface materials. Surface-wave methods based on inversions of dispersion curves are only suitable to laterally homogeneous or smoothly laterally varying heterogeneous earth models due to the layered-model assumption during calculation of dispersion curves. Waveform inversion directly fits the waveform of observed data, and it can be applied to any kinds of earth models. We have used the Love-wave waveform inversion in the time domain to estimate near-surface S-wave velocity. We used the finite-difference method as the forward modeling method. The source effect was removed by the deconvolution technique, which made our method independent of the source wavelet. We defined the difference between the deconvolved observed and calculated waveform as the misfit function. We divided the model into different sizes of blocks depending on the resolution of the Love waves, and we updated the S-wave velocity of each blo...

57 citations

Journal ArticleDOI
TL;DR: In this article, a state-of-the-art review of MASW and shallow-seismic FWI and a comparison of both methods is provided. But the authors focus on the nonlinearity and resolution of the two methods.
Abstract: Surface waves are widely used in near-surface geophysics and provide a noninvasive way to determine near-surface structures. By extracting and inverting dispersion curves to obtain local 1D S-wave velocity profiles, multichannel analysis of surface waves (MASW) has been proven as an efficient way to analyze shallow-seismic surface waves. By directly inverting the observed waveforms, full-waveform inversion (FWI) provides another feasible way to use surface waves in reconstructing near-surface structures. This paper provides a state of the art review of MASW and shallow-seismic FWI and a comparison of both methods. A two-parameter numerical test is performed to analyze the nonlinearity of MASW and FWI, including the classical, the multiscale, the envelope-based, and the amplitude-spectrum-based FWI approaches. A checkerboard model is used to compare the resolution of MASW and FWI. These numerical examples show that classical FWI has the highest nonlinearity and resolution among these methods, while MASW has the lowest nonlinearity and resolution. The modified FWI approaches have an intermediate nonlinearity and resolution between classical FWI and MASW. These features suggest that a sequential application of MASW and FWI could provide an efficient hierarchical way to delineate near-surface structures. We apply the sequential-inversion strategy to two field data sets acquired in Olathe, Kansas, USA, and Rheinstetten, Germany, respectively. We build a 1D initial model by using MASW and then apply the multiscale FWI to the data. High-resolution 2D S-wave velocity images are obtained in both cases, whose reliabilities are proven by borehole data and a GPR profile, respectively. It demonstrates the effectiveness of combining MASW and FWI for high-resolution imaging of near-surface structures.

52 citations

Journal ArticleDOI
TL;DR: In this article, the authors defined two mode types based on the characteristics of the vertical eigendisplacements calculated by generalized reflection and transmission coefficient method, which is commonly seen in near-surface earth models.
Abstract: Identifying correct modes of surface waves and picking accurate phase velocities are critical for obtaining an accurate S-wave velocity in MASW method. In most cases, inversion is easily conducted by picking the dispersion curves corresponding to different surface-wave modes individually. Neighboring surface-wave modes, however, will nearly meet (kiss) at some frequencies for some models. Around the frequencies, they have very close roots and energy peak shifts from one mode to another. At current dispersion image resolution, it is difficult to distinguish different modes when mode-kissing occurs, which is commonly seen in near-surface earth models. It will cause mode misidentification, and as a result, lead to a larger overestimation of S-wave velocity and error on depth. We newly defined two mode types based on the characteristics of the vertical eigendisplacements calculated by generalized reflection and transmission coefficient method. Rayleigh-wave mode near the kissing points (osculation points) change its type, that is to say, one Rayleigh-wave mode will contain different mode types. This mode type conversion will cause the mode-kissing phenomenon in dispersion images. Numerical tests indicate that the mode-kissing phenomenon is model dependent and that the existence of strong S-wave velocity contrasts increases the possibility of mode-kissing. The real-world data shows mode misidentification caused by mode-kissing phenomenon will result in higher S-wave velocity of bedrock. It reminds us to pay attention to this phenomenon when some of the underground information is known.

43 citations

Journal ArticleDOI
TL;DR: In this article, the authors proposed a method to calculate Rayleigh-wave phase velocities of models with a high-velocity surface layer by considering its penetration depth, which is the layer with the lowest S-wave velocity among the layers above the half-space.

40 citations

Journal ArticleDOI
TL;DR: In this paper, a passive source surface-wave survey along a 70 km-long line on the western side of the Junggar basin in northwest China was conducted, where frequency-time analysis and spatial autocorrelation methods were used to extract surface wave dispersion curves from ambient noise data of station pairs, as well as ambient noise multichannel analysis of surface waves from multistations.
Abstract: Aiming for a geophysical survey to around 1.5 km depth, we conduct a passive‐source surface‐wave survey along a 70‐km‐long line on the western side of the Junggar basin in northwest China. We use frequency–time analysis and spatial autocorrelation methods to extract surface‐wave dispersion curves from ambient‐noise data of station pairs, as well as ambient‐noise multichannel analysis of surface waves from multistations. Dispersion curves corresponding to the same positions obtained by these three methods independently are comparable, which shows the validity of using these methods. After inverting more than 400 dispersion curves and aligning their results together, we construct a 2D shear S ‐wave velocity image around 1.5 km deep and 60 km long. A less than 6% difference between the inverted S ‐wave velocity profile and the borehole data in situ shows the relatively high accuracy of our method. The 2D S ‐wave velocity image clearly delineates the main geologic structures, including transition of landform, intrusion of rock mass, and shape of bedrock beneath the survey line.

36 citations


Cited by
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Journal ArticleDOI
TL;DR: This study reports the first end-to-end study of time-lapse VS imaging that uses traffic noise continuously recorded on linear DAS arrays over a three-week period, demonstrating the efficacy of near-surface seismic monitoring using DAS-recorded ambient noise.
Abstract: Ambient-noise-based seismic monitoring of the near surface often has limited spatiotemporal resolutions because dense seismic arrays are rarely sufficiently affordable for such applications. In recent years, however, distributed acoustic sensing (DAS) techniques have emerged to transform telecommunication fiber-optic cables into dense seismic arrays that are cost effective. With DAS enabling both high sensor counts (“large N”) and long-term operations (“large T”), time-lapse imaging of shear-wave velocity (V S ) structures is now possible by combining ambient noise interferometry and multichannel analysis of surface waves (MASW). Here we report the first end-to-end study of time-lapse V S imaging that uses traffic noise continuously recorded on linear DAS arrays over a three-week period. Our results illustrate that for the top 20 meters the V S models that is well constrained by the data, we obtain time-lapse repeatability of about 2% in the model domain—a threshold that is low enough for observing subtle near-surface changes such as water content variations and permafrost alteration. This study demonstrates the efficacy of near-surface seismic monitoring using DAS-recorded ambient noise.

260 citations

Journal ArticleDOI
TL;DR: In this article, a multichannel analysis of high-frequency surface (Rayleigh and Love) waves developed mainly by research scientists at the Kansas Geological Survey, the University of Kansas and China University of Geosciences (Wuhan) during the last eighteen years by discussing dispersion imaging techniques, inversion systems, and real-world examples.

118 citations

Patent
29 Aug 2008
TL;DR: In this article, an apparatus, a method and a recording medium for imaging an underground structure using waveform inversion of a Laplace-Fourier domain are provided to stably obtain a speed model with long wavelength information and middle wavelength information.
Abstract: PURPOSE: An apparatus, a method and a recording medium for imaging an underground structure using waveform inversion of a Laplace-Fourier domain are provided to stably obtain a speed model with long wavelength information and middle wavelength information. CONSTITUTION: An apparatus for imaging an underground structure using waveform inversion of a Laplace-Fourier domain includes a receiver and a signal processing unit. The signal processing unit comprises an input unit, a converting unit(202), a modeling data generating unit(203), and a parameter update unit(206). The converting unit converts measurement data in a time domain into measurement data in a Laplace-Fourier domain using an attenuation constant of a complex number. The modeling data generating unit sets an equation including a parameter by receiving a parameter showing a feature of a measurement target region. The modeling data generating unit calculates the equation in the Laplace-Fourier domain to calculate modeling data.

102 citations

Journal ArticleDOI
TL;DR: Wang et al. as discussed by the authors proposed the frequency-Bessel transform method (F-J method) for extracting the dispersion curves of higher modes from ambient seismic noise data.
Abstract: Author(s): Wang, J; Wu, G; Chen, X | Abstract: ©2019. American Geophysical Union. All Rights Reserved. It has been widely recognized that the cross-correlation function of ambient seismic noise data recorded at two stations approximates to the part of Greens function between two stations. Therefore, the cross-correlation function should include higher modes, aside from the fundamental mode. However, the problem of measuring or extracting overtones from ambient seismic noise data remains. In this paper, we propose the frequency-Bessel transform method (F-J method) for extracting the dispersion curves of higher modes from ambient seismic noise data. We then assess the validity, accuracy, and applicability of the F-J method by conducting extensive numerical simulations and processing the observed ambient seismic noise data of the USArray. As demonstrated in this study, the F-J method is a convenient, practical, and accurate method for extracting the dispersion curves of multimodes from ambient seismic noise data and therefore has significant potentiality in the field of ambient seismic noise tomography.

86 citations

Journal ArticleDOI
TL;DR: In this paper, the authors used geophysics to characterize spatial and temporal variability in the subsurface region proximal to SW bodies, the GW-SW interface, which is crucial as it actively regulates the transfer of nutrients, contaminants, and water between GW systems and SW environments.

78 citations