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The Hangay Dome in central Mongolia, a typical intraplate plateau far from plate boundaries, is characterized by rapid uplift and widespread volcanic activities in the Cenozoic. However, thermodynamics process for the landform in Cenozoic remains mysterious. Seismic Lg-wave, which is sensitive to crustal thermal status, can provide constraints on the crustal attenuation structure; thus, may be helpful to understand the thermodynamics. In this study, we estimate the Lg-wave quality factor QLg across the Hangay Dome and its surroundings from 231 crustal earthquakes recorded by 136 regional broadband seismic stations distributed throughout north China and Mongolia. Using a joint tomographic method, we construct a broadband Lg attenuation model at 58 discrete frequencies distributed evenly in log scale between 0.1 and 20.0 Hz. The obtained QLg model provides new insights into crustal attenuation in the region. The strong Lg wave attenuation observed in the northeastern Hangay Dome and western Gobi-Altai, associated with crust low-resistivity anomalies, low S-wave velocity region, heat flow and volcanic activities, suggest the existence of possible partial melting due to asthenospheric upwelling. The widespread moderately-low QLg values around the perimeter of the Hangay Dome imply that the margin of the Hangay Dome has been weakened. The center part of the uplift is a small high QLg nucleus, which is possibly the residue of the Precambrian basement. The above observations suggest that the Hangay Dome is lifted by small-scale asthenospheric upwellings. During this process, the very hot mantle materials strongly modified the Hangar Dome and also caused the Cenozoic volcanism and major earthquakes. [ABSTRACT FROM AUTHOR]

We propose a method based on the Poynting vector that combines angle-domain imaging and image amplitude correction to overcome the shortcomings of reverse-time migration that cannot handle different angles during wave propagation. First, the local image matrix (LIM) and local illumination matrix are constructed, and the wavefield propagation directions are decomposed. The angle-domain imaging conditions are established in the local imaging matrix to remove low-wavenumber artifacts. Next, the angle-domain common image gathers are extracted and the dip angle is calculated, and the amplitude-corrected factors in the dip angle domain are calculated. The partial images are corrected by factors corresponding to the different angles and then are superimposed to perform the amplitude correction of the final image. Angle-domain imaging based on the Poynting vector improves the computation efficiency compared with local plane-wave decomposition. Finally, numerical simulations based on the SEG/EAGE velocity model are used to validate the proposed method. [ABSTRACT FROM AUTHOR]

Seismic migration moves reflections to their true subsurface positions and yields seismic images of subsurface areas. However, due to limited acquisition aperture, complex overburden structure and target dipping angle, the migration often generates a distorted image of the actual subsurface structure. Seismic illumination and resolution analyses provide a quantitative description of how the above-mentioned factors distort the image. The point spread function (PSF) gives the resolution of the depth image and carries full information about the factors affecting the quality of the image. The staining algorithm establishes a correspondence between a certain structure and its relevant wavefield and reflected data. In this paper, we use the staining algorithm to calculate the PSFs, then use these PSFs for extracting the acquisition dip response and correcting the original depth image by deconvolution. We present relevant results of the SEG salt model. The staining algorithm provides an efficient tool for calculating the PSF and for conducting broadband seismic illumination and resolution analyses. [ABSTRACT FROM AUTHOR]

The first-order (or linear) Rytov or Born approximation is the foundation for formulation of wave-equation tomography and waveform inversion, so the validity of the Rytov/Born approximation can substantially affect the applicability of these theories. However, discussions and research reported in literature on this topic are insufficient or limited. In this paper we introduce five variables in scattering theory to help us discuss conditions under which the Rytov approximation, in the form of the finite frequency sensitivity kernels (RFFSK), the basis of waveform inversion and tomography, is valid. The five variables are propagation length L, heterogeneity scale a, wavenumber k, anisotropy ratio ξ, and perturbation strength ɛ. Combined with theoretical analysis and numerical experiments, we conclude that varying the conditions used to establish the Rytov approximation can lead to uninterpretable or undesired results. This conclusion has two consequences. First, one cannot rigorously apply the linear Rytov approximation to all theoretical or practical cases without discussing its validity. Second, the nonlinear Rytov approximation is essential if the linear Rytov approximation is not valid. Different from previous literature, only phase (or travel time) terms for the whole wavefield are discussed. The time shifts of two specific events between the background and observed wavefields measured by cross-correlation will serve as a reference for evaluation of whether the time shifts predicted by the FFSKs are reasonably acceptable. Significantly, the reference 'cross-correlation' should be regarded as reliable only if the condition 'two specific similar signals' is satisfied. We cannot expect it to provide a reasonable result if this condition is not met. This paper reports its reliability and experimental limitations. Using cross-correlation (CC) samples as the X axis and sensitivity kernel (SK) or ray tracing (RT) samples as the Y axis, a chart of cross validation among the three is established. According to experimental analysis for a random and deterministic medium, the RFFSK works well for diffraction and geometric optics enclosed by the boundaries ka > 1 and (Λ < 1, ΛΦ < 2 π ∪ Λ > 1, Φ < 2 π), where Λ is a diffraction variable and Φ is a variable used to measure scattering strength. Both Λ and Φ depend on the five variables mentioned above. However, a large perturbation will limit the applicability of the Rytov approximation and narrow the range in which it is valid, because larger ɛ results in higher-amplitude fluctuations and larger back-scattering. Therefore, large ɛ is important in making SK/RT predictions discrepant from correct CC measurements. We also confirm that the RFFSK theory has wider range of application than ray theory. All the experiments point out the importance, both practical and theoretical, of respecting the conditions used to establish the Rytov approximation. [ABSTRACT FROM AUTHOR]