Seismic Imaging Research Articles

A high-efficiency Q-compensated pure-viscoacoustic reverse time migration for tilted transversely isotropic media

The attenuation and anisotropy characteristics of real earth media give rise to amplitude loss and phase dispersion during seismic wave propagation. To address these effects on seismic imaging, viscoacoustic anisotropic wave equations expressed by the fractional Laplacian have been derived. However, the huge computational expense associated with multiple Fast Fourier transforms for solving these wave equations makes them unsuitable for industrial applications, especially in three dimensions. Therefore, we first derived a cost-effective pure-viscoacoustic wave equation expressed by the memory-variable in tilted transversely isotropic (TTI) media, based on the standard linear solid model. The newly derived wave equation featuring decoupled amplitude dissipation and phase dispersion terms, can be easily solved using the finite-difference method (FDM). Computational efficiency analyses demonstrate that wavefields simulated by our newly derived wave equation are more efficient compared to the previous pure-viscoacoustic TTI wave equations. The decoupling characteristics of the phase dispersion and amplitude dissipation of the proposed wave equation are illustrated in numerical tests. Additionally, we extend the newly derived wave equation to implement Q-compensated reverse time migration (RTM) in attenuating TTI media. Synthetic examples and field data test demonstrate that the proposed Q-compensated TTI RTM effectively migrate the effects of anisotropy and attenuation, providing high-quality imaging results.

The Influence of Mantle Structure on Dynamic Topography in Southern Africa

AbstractDue to relatively high terrain and negligible active tectonics, the southern Africa region boasts over 30 independent estimates of dynamic topography. These published estimates display a wide variance due to both the variety of methods used in computation and a lack of constraints on the regional mantle structure. Here we show that a focus on regional mantle structure is important to generate models of lithospheric and mantle dynamics. Global average mantle properties are not representative of a particular region, and it is necessary to generate viscosity profiles specific to a region of interest. We develop a Bayesian inversion using dynamic geoid kernels, existing seismic tomography models, and Slepian functions to invert for a localized radial viscosity profile that best explains the geoid in southern Africa. With an understanding of viscosity uncertainty, we constrain dynamic topography in southern Africa to lie between 1,000 and 2,000 m. Additionally, we model vertical displacements from 112 Global Navigation Satellite System stations across our region to examine the long‐term, long wavelength pattern of present‐day vertical motion, suggesting that a mean of 1.5 mm/yr (1: 0.8–2.0 mm/yr) of vertical motion may be related to ongoing dynamic topography. Our study demonstrates the utility of dynamic geoid kernels in local nonlinear inversions of non‐unique geophysical data. Furthermore, we present evidence that the mantle beneath southern Africa is generating significant dynamic support for and vertical displacement of the lithosphere in this region.

The impact of Pangean subducted oceans on mantle dynamics: Passive piles and the positioning of deep mantle plumes

Seismic imaging of the Earth’s interior reveals plumes originating from relatively hot regions of the lowermost mantle, surrounded by cooler material thought to be remnants of ancient subducted oceans. Currently, there is no clear consensus on the internal composition of the hot regions, with end-member conditions being that they are thermo-chemical in nature or purely thermal plume clusters. Previous modelling studies have shown a range of scenarios where deep chemical heterogenities or purely thermal anomalies are essential in developing appropriate present-day mantle dynamics. Here, we add to this discus- sion by quantifying the location of rising mantle plumes using numerical 3-D global mantle convection models constrained by 410 million years of palaeo-ocean evolution (encompassing the formation and breakup of supercontinent Pangea). Our study compares numerical simulations with purely thermal convection to those where a deep thermo-chemical anomaly is laterally mobile. The results show that models both with and without large-scale chemical heterogeneities can generate appropriate present-day plume dynamics, which illustrate the power of sinking ocean plates to stir mantle ow and control the thermal evolution of the mantle. Our models add to the discussion on bottom-up and top-down mantle dynamics, indicating the difficulty in unravelling the processes using numerical models alone.

Application of vertical seismic profile multi-component data to tight sandstone gas reservoirs

Abstract Given the complex geological characteristics of the tight gas sandstone in the Shaximiao Formation of the Jurassic in the central Sichuan Basin, including its wide distribution, narrow width, and thin thickness, conventional surface seismic methods face significant challenges in reservoir delineation. To address this challenge, a vertical seismic profile (VSP) survey was conducted in the region in 2022, along with the simultaneous collection of 3D3C surface seismic data. This article mainly elaborates on a case study of using multi-component VSP technology to delineate tight sandstone gas reservoirs. By comparing the processed VSP imaging volume with the surface seismic imaging volume, it was discovered that the frequency width of the VSP image was 8 to 12 Hz higher than that of the surface seismic image. Utilizing the multi-component information in VSP data, it is feasible to more precisely delineate tight gas sandstones, thereby reducing the uncertainty of data interpretation. Based on the conventional data interpretation of these images, an innovative application suggests using the centroid frequency ratio of PSv to PP waves as an indicator for tight sandstone. The results show that this attribute has high sensitivity to this type of reservoir. Combining geological, drilling, and logging data, an interpretation template was established based on VSP data to interpret 3D3C surface seismic data and propose new drilling well locations. The conclusion is that the successful application of VSP technology cannot be achieved without the integration of multiple disciplines. The combined exploration technology of multi-component VSP and 3D3C surface seismic has been demonstrated to have high application value through practical application, significantly improving the success rate of gas wells and providing effective support for the exploration and development of tight sandstone gas reservoirs.

Modeling Rayleigh wave in viscoelastic media with constant Q model using fractional time derivatives

The propagation of seismic waves within the near-surface weathering layers, characterized by their low-quality factors (Q), is often accompanied by strong attenuation and dispersion phenomena. Among these, the Rayleigh wave, with its sensitivity to dispersion, has proven to be a powerful tool for near-surface exploration. We propose a novel approach for simulating Rayleigh wave propagation in such low-Q media. Our method uses the time-domain fractional wave equation with memory effect, based on Kjartansson's constant-Q (CQ) model, for accurate characterization of the propagation process. To solve numerically the wave equation with the fractional derivatives, we employ a finite-difference method combined with the auxiliary differential equation-perfectly matched layer (ADE-PML) and the acoustic-elastic boundary approach (AEA). The algorithm's high computational accuracy is verified through comparison with the conventional integer-order wave equation based on the nearly constant-Q (NCQ) models in strong attenuation media. The research in this paper deepens our understanding of the propagation characteristics of Rayleigh waves in strongly weathering layers. This new method strongly supports those seismic imaging and inversion methods depending on seismic modeling, including the reverse time migration and the full waveform inversion of the internal structure of low-Q media.

Application of Experimental Configurations of Seismic and Electric Tomographic Techniques to the Investigation of Complex Geological Structures

The main purpose of this study is the subsurface investigation of two complex geological environments focusing on the improvement of data acquisition and processing parameters regarding electric and seismic tomographic techniques. Two different study areas, in central–east Peloponnese and SE Attica, were selected, where detailed geological mapping and surface geophysical survey were carried out. The applied geophysical survey included the application of electrical resistivity tomography (ERT), seismic refraction tomography (SRT) and ground penetrating radar (GPR). The geoelectrical measurements were acquired with different arrays and electrode configurations. Moreover, various types of seismic sources were used at seventeen shot locations along the seismic arrays. For the processing of geoelectrical data, clustered datasets were created, increasing the depth of investigation and discriminatory capability. The seismic data processing included the following: (a) the creation of synthetic models and seismic records to determine the effectiveness and capabilities of the technique, (b) spectral analysis of the seismic records to determine the optimal seismic source type and (c) inversion of the field data to create representative subsurface velocity models. The results of the two techniques successfully delineated the complex subsurface structure that characterizes these two geological environments. The application of the ERT combined with the SRT are the two dominant, high-resolution techniques for the elucidation of complex subsurface structures.

Cenozoic Evolution of the Rongcheng High from High-Resolution 3D Seismic Reflection Imaging

Cenozoic Evolution of the Rongcheng High from High-Resolution 3D Seismic Reflection Imaging

Revealing the Internal Structure of the Great Tumulus of Apollonia by Means of Seismic Tomography

ABSTRACTThe Great Tumulus of Apollonia in northern Greece, with a diameter of ~100 m and a height of 19 m, is among the largest of its kind in the region of the ancient kingdom of Macedonia. It is located north of the ancient city of Apollonia and recently became the focus of limited archaeological excavations, which revealed a looted Macedonian tomb. Archaeological findings and other evidence from the tumulus and its surroundings suggest that it may have been used more than once; therefore, the existence of more tombs in its interior is possible. In this work, we investigate the internal structure of the monument by means of 3‐D seismic travel time tomography. Using direct sparse methods, we calculate efficiently the full model resolution matrix that allows us to investigate the robustness of the tomographic model. Our results suggest a complex structure with variable properties between the east and the western side of the tumulus. We also detect several regions that may be associated with additional burial locations or other possible targets of archaeological interest.

A microlocal and visual comparison of 2D Kirchhoff migration formulas in seismic imaging*

Abstract The term Kirchhoff migration refers to a collection of approximate linearized inversion formulas for solving the inverse problem of seismic tomography which entails reconstructing the Earth’s subsurface from reflected wave fields. A number of such formulas exists, the first dating from the 1950 s. As far as we know, these formulas have not yet been mathematically compared with respect to their imaging properties. This shortcoming is to be alleviated by the present work: we systematically discuss the advantages and disadvantages of the formulas in 2D from a microlocal point of view. To this end we consider the corresponding imaging operators in an unified framework as pseudodifferential or Fourier integral operators. Numerical examples illustrate the theoretical insights and allow a visual comparison of the different formulas.

Engineering geological investigation of Gololcha dam for evaluation of leakage and abutment slope stability, Eastern Ethiopia

The Ethiopian economy is primarily dependent on agriculture, making the construction of water harvesting facilities, such as dams, crucial for improving the productivity of this sector. The ongoing construction of the Gololcha dam on the Kurkura River located in Eastern Ethiopia aims to enhance irrigation schemes in the region. However, the dam site's complex geological and structural conditions pose challenges related to leakage and slope instability. Hence, this study focuses on addressing the abutment slope stability and leakage condition of this dam. This study employed kinematic analysis and the Limit Equilibrium Method (LEM) to assess slope stability. Additionally, engineering geological mapping, discontinuity surveys, seismic refraction tomography (SRT), and in-situ permeability testing were used to evaluate the leakage condition of the dam site. Notably, the permeability and SRT survey results identified potential leakage zones to the depth of 35, 30, and 35 m at the left, right, and central foundations of the dam, respectively. The kinematic method revealed one planar and two wedge modes of failure in the slope section covered by slightly weathered and fractured basalt rock at the right abutment. Further stability analysis of these two modes of failures via LEM analysis indicated slope instability under saturated conditions, emphasizing the role of pore water pressure. Furthermore, LEM modeling was directly utilized using the Slide 6.0 software to analyze the slope stability condition of the left abutment of the dam. This modeling also uncovered instability under saturated conditions. Based on the study findings, this study recommended curtain grouting to address potential leakage, as well as slope flattening and removing unstable rock wedges and loose material to stabilize unstable slope sections.

Accurate identification of salt domes using deep learning techniques: Transformers, generative artificial intelligence and liquid state machines

AbstractAcross various global regions abundant in oil and natural gas reserves, the presence of substantial sub‐surface salt deposits holds significant relevance. Accurate identification of salt domes becomes crucial for enterprises engaged in oil and gas exploration. Our research introduces a precise method for the automatic detection of salt domes, leveraging advanced deep learning architectures such as U‐net, transformers, artificial intelligence generative models and liquid state machines. In comparison with state‐of‐the‐art techniques, our model demonstrates superior performance, achieving a stable and validated intersection over the union metric, indicating high accuracy and robustness. Furthermore, the Dice similarity coefficient attaining underscores the model's proficiency in closely aligning with ground truth across diverse scenarios. This evaluation, conducted on 1000 seismic images, reveals that our proposed architecture is not only comparable but often surpasses existing segmentation models in effectiveness and reliability.

Seismic Imaging of the Arctic Subsea Permafrost Using a Least-Squares Reverse Time Migration Method

High-resolution seismic imaging allows for the better interpretation of subsurface geological structures. In this study, we employ least-squares reverse time migration (LSRTM) as a seismic imaging method to delineate the subsurface geological structures from the field dataset for understanding the status of Arctic subsea permafrost structures, which is pertinent to global warming issues. The subsea permafrost structures in the Arctic continental shelf, located just below the seafloor at a shallow water depth, have an abnormally high P-wave velocity. These structural conditions create internal multiples and noise in seismic data, making it challenging to perform seismic imaging and construct a seismic P-wave velocity model using conventional methods. LSRTM offers a promising approach by addressing these challenges through linearized inverse problems, aiming to achieve high-resolution, subsurface imaging by optimizing the misfit between the predicted and the observed seismic data. Synthetic experiments, encompassing various subsea permafrost structures and seismic survey configurations, were conducted to investigate the feasibility of LSRTM for imaging the Arctic subsea permafrost from the acquired seismic field dataset, and the possibility of the seismic imaging of the subsea permafrost was confirmed through these synthetic numerical experiments. Furthermore, we applied the LSRTM method to the seismic data acquired in the Canadian Beaufort Sea (CBS) and generated a seismic image depicting the subsea permafrost structures in the Arctic region.

Calculating traveltimes in 2D general tilted transversely isotropic media using fast sweeping method

Traveltime calculations play an important role in the field of exploration seismology, such as traveltime tomography and seismic imaging and so on. Seismic anisotropy poses a challenge for traveltime calculation, because anisotropic eikonal solvers are more complex than the isotropic counter part. To solve the eikonal equations in 2D tilted transversely isotropic (TTI) media, we have developed a fast algorithm combine with fast sweeping method to compute the first arrival traveltimes of quasi-P (qP)-, quasi-SV (qSV)-, and quasi-SH(qSH)-waves. For the qP- and qSV-waves, we analyzed the quartic coupled slowness surface equation derived from the Christoffel equation. Then, we constructed a local solver to relate traveltime and slowness. We found that in the local solver, one component of the slowness vector is known and the corresponding slowness equation is monotonic. This provides a strong basis for the fast iterative algorithm we proposed, where we use the Newton method to solve the qP- and qSV-wave slowness equation to determine the related traveltimes. For the qSH wave, the slowness equation is quadratic and simple to solve. Numerical experiments demonstrate that the proposed method can obtain accurate traveltimes for simple and complicated 2D TTI models.

The effect of pre-existing structures on the Cenozoic rifting processes: Insights from seismic reflection imaging of the northeastern south China sea

The South China Sea (SCS) opened due to the extension of a compressional setting of the paleo-Pacific subduction. The pre-existing structure significantly influences the geometry of rift basins and the kinematic evolution of the rifting. However, structural evidence of the paleo-Pacific subduction in the northeastern SCS remains enigmatic. The deformation front, serving as the structural evidence of paleo-subduction, is associated with accretionary style deformation and would be reactivated during the subsequent extension phase. In this study, we use a multi-channel seismic profile to investigate the pre-existing structure related to the paleo-Pacific subduction in the northeastern SCS, emphasizing the influence of pre-existing structure on the rift evolution. The seismic profile reveals imbricate reflections in the lower crust. These reflections are interpreted as the deformation front of the Paleo-Pacific subduction. Notably, the deformation front is hyperextended in the Chaoshan Depression. The result of the stretching factors indicates that the ductile lower crust experienced preferential thinning during the rifting beneath the Chaoshan Depression. In the northern part of the profile, a transparent reflection zone was identified and interpreted as a magmatic arc related to Mesozoic subduction. One major achievement of our study is these seismic reflections provide the structural evidence for Paleo-Pacific subduction and reveal that the northeastern SCS has experienced crustal shortening and imbrication through a series of dipping thrusts. Subsequently, we discuss the role of pre-existing structures in lower crustal thinning and continental rifting. We propose the deformation front of the Mesozoic subduction, as a pre-existing weakness, facilitated the kinematic evolution of the rifting in the northeastern SCS during the Cenozoic.

Seismic tomography reveals contrasting styles of subduction-channel and mantle-wedge exhumation controlled by upper plate divergent motion

In fossil subduction zones associated with massive exhumation of (ultra)high-pressure ((U)HP) rocks such as the Western Alps, the geometry and behavior of subduction-channel and mantle-wedge rocks during exhumation are still poorly constrained by independent geophysical observations. Here we use a new local earthquake tomography model of the entire fossil subduction zone of the Western Alps based on data collected during the CIFALPS and CIFALPS2 passive seismic experiments, and the first receiver-function profile across the Ligurian Alps, to investigate the styles of subduction-channel and mantle-wedge exhumation as a function of increasing upper-plate divergence motion. In the northern Western Alps (low divergence), a thickened subduction channel can be detected, but no exhumed mantle wedge is found beneath the Gran Paradiso (U)HP dome. In the southern Western Alps (intermediate divergence), an exhumed mantle wedge is detected beneath the Dora-Maira (U)HP dome above a serpentinized subduction channel. In the Ligurian Alps (high divergence), an exhumed mantle wedge and a former subduction channel are detected at much shallower levels beneath the Voltri-Valosio (U)HP dome, and above a shallow-dipping lower-plate Moho. In this latter case, the lower boundary of the exhumed subduction channel is the most evident seismic-velocity interface, which may be easily misinterpreted as a true Moho. Similar Moho-like interfaces are found beneath the exhumed (U)HP domes of eastern Papua New Guinea and the Dabie Shan, which suggests that the results of the CIFALPS experiments may be used as a reference case for the interpretation of other (U)HP terranes worldwide.

Reservoir oriented migrated seismic image improvement and poststack seismic inversion using well-seismic mistie

In seismic exploration of subsurface hydrocarbon reservoirs, migrated seismic image is the foundation for structural interpretation and subsequent seismic inversion for reservoir properties. Seismic events in migrated images can be mispositioned due to several factors including seismic velocity inaccuracy. The mispositioned events lead to poor well-seismic tie and degrades the accuracy of subsequent inversion and reservoir prediction. Particularly, the mistie can be quite obvious for the mid- and mature- phases of the reservoir development after many wells drilled. We propose to utilize the information from mistie between seismic images and synthetic traces to improve the accuracy of migrated seismic images and thus inversion results. Our method includes three major steps: firstly, calculate time shifts between the synthetic traces and the co-located seismic trace using the path-limited dynamic time warping (PDTW) algorithm; then compute the time shift volume for the entire migrated image using the seismic-driven modeling approach based on the time shift traces at the well locations; apply the time shift volume to update the migrated image. The improved seismic volume can be used for further processing such as seismic inversion, which makes the inversion results more consistent with seismic and well data. We apply our method to synthetic and field datasets. The results demonstrate that the updated seismic image has an improved seismic well tie and an improved inversion result. Our method indicates a venue for a better honor of seismic and well data in reservoir characterization.

Seismic traveltime tomography based on ensemble Kalman inversion

SUMMARY In this paper, we present a new seismic traveltime tomography approach that combines ensemble Kalman inversion (EKI) with neural networks (NNs) to facilitate the inference of complex underground velocity fields. Our methodology tackles the challenges of high-dimensional velocity models through an efficient NN parametrization, enabling efficient training on coarse grids and accurate output on finer grids. This unique strategy, combined with a reduced-resolution forward solver, significantly enhances computational efficiency. Leveraging the robust capabilities of EKI, our method not only achieves rapid computations but also delivers informative uncertainty quantification for the estimated results. Through extensive numerical experiments, we demonstrate the exceptional accuracy and uncertainty quantification capabilities of our EKI-NNs approach. Even in the face of challenging geological scenarios, our method consistently generates valuable initial models for full wave inversion (FWI).

Cross-gradient joint inversion and clustering of ERT and SRT data on structured meshes incorporating topography

Summary The combination of electrical resistivity and seismic refraction tomography is a common practice for the characterization of subsurface features. Presently, the cross-gradient inversion scheme stands out as one of the most robust joint approaches, and some authors modified it to manage complex topographies on unstructured meshes even if at the expense of introducing additional parameters in the inversion process. We propose in this work a cross-gradient algorithm for jointly inverting electrical and seismic tomographic data on structured meshes in cases with non-flat topography. The proposed approach preserves the benefit of the classical cross-gradient approach without the need to impose physical length scales, as for irregular meshes. The quality of the results is evaluated in comparison with independent inversion through a new standardized cross-gradient index and a fuzzy c-means analysis that provides an assessment of the reconstruction accuracy through the membership function. The proposed method was applied to both synthetic models and field-scale examples located in Central Italy, where an accurate geophysical reconstruction is needed for the rehabilitation of existing dams. For all cases, joint inversion yielded superior results compared to independent inversion, demonstrating better agreement with available borehole data. The effectiveness of the joint approach was also demonstrated by the post-inversion tools, where the new cross-gradient index highlighted changes in structural similarity whilst fuzzy c-means clustering allowed for a quantitative reconstruction (position and shape) of the main units at the sites, facilitating the detection of site layering modifications.

Assessing the effect of offline topography on electrical resistivity measurements: insights from flood embankments

Summary Electrical resistivity tomography (ERT), a geophysical imaging method, is commonly used on flood embankments (dykes or levees) to characterise their internal structure and look for defects. These surveys often use a single line of electrodes to enable 2D imaging through the embankment crest, an approach that enables rapid and efficient surveying compared to 3D surveys. However, offline variations in topography can introduce artefacts into these 2D images, by affecting the measured resistivity data. Such topographic effects have only been explored on a site-specific basis. If the topographic effects can be assessed for a distribution of embankment geometries (e.g. slope angle and crest width) and resistivity variations, it would allow for targeted correction procedures and improved survey design. To investigate topographic effects on ERT measurements, we forward-modelled embankments with different trapezoidal cross-sections sat atop a flat foundation layer with contrasting resistivity values. Each was compared to a corresponding flat model with the same vertical resistivity distribution. The modelling workflow was designed to minimise the effect of forward modelling errors on the calculation of topographic effect. We ran 1872 unique embankment forward models, representing 144 geometries, each with 13 different resistivity contrasts. Modelling results show that offline topography affects the tested array types (Wenner-Schlumberger, Dipole-Dipole, and Multiple-Gradient) in slightly different ways, but the magnitudes are similar, so all are equally suitable for embankment surveys. Three separate mechanisms are found to cause topographic effects. The dominant mechanism is caused by the offline topography confining the electrical current flow, increasing the measured transfer resistance from the embankment model. The two other mechanisms, previously unidentified, decrease the measured transfer resistances from the embankment model compared to a layered half-space but only affect embankments with specific geometries and resistivity distributions. Overall, we found that for typical embankment geometries and resistivity distributions, the resistivity distribution has a greater control on the magnitude of the topographic effect than the exact embankment geometry: the subsurface resistivity distribution cannot be neglected. 2D inversions are suitable when both the embankment is more resistive than the foundations and when the embankment's cross-sectional area is greater than 4 m2/m2 (area scaled to an embankment with a height of 1 m). Topographic corrections, 3D data acquisition or 3D forward models are required when these conditions are not met. These are demonstrated using field data from an embankment at Hexham, Northumberland, UK. Improving the accuracy of the resistivity values in ERT models will enable more accurate ground models, better integration of resistivity data with geotechnical datasets, and will improve the translation of resistivity values into geotechnical properties. Such developments will contribute to a better characterised and safer flood defence network.

The overdetermined Cauchy problem for the hyperbolic Gellerstedt equation

Abstract Overdetermined boundary value problems and the minimal operators generated by them are extremely important in the description of regular boundary value problems for differential equations, and are also widely used in the study of local properties of solutions. In addition, for inverse problems of mathematical physics arising from applications, when determining unknown data, it is necessary to study problems with overdetermined boundary conditions, which is reflected in the study of problems, including for hyperbolic equations and systems, arising in physics, geophysics, seismic tomography, geoelectrics, electrodynamics, medicine, ecology, economics and many other practical areas. Thus, the study of overdetermined boundary value problems is of both theoretical and applied interest. In this paper, a criterion for the regular solvability of the overdetermined Cauchy problem for the Gellerstedt equation and the minimal differential operator generated by it in a hyperbolic domain is established, as which both the case of a characteristic triangle and the case of a more general domain with fairly general assumptions about the boundary of the domain are considered. Due to overdetermined boundary conditions, the problem under consideration will be ill-posed in the general case, therefore, for its regular solvability, additional conditions must be imposed on the initial data. In other words, we have considered the inverse problem: to determine what requirements the initial data of the problem, in particular the right part of the Gellerstedt equation, should meet, in question, so that the overdetermined Cauchy problem is regularly solvable. The proof is based on the Gellerstedt potential, the properties of solutions of the Goursat problem in the characteristic triangle, and the properties of special functions.