Common Reflection Surface Research Articles

Common Reflection Surface Stack Imaging of the Proterozoic Chambal Valley Vindhyan Basin and Its Boundary Fault in the Northwest India: Constraints on Crustal Evolution and Basin Formation

AbstractThe Vindhyan basin of northwestern and central India is one of the largest undeformed Meso‐Neoproterozoic basins in the world with likely potential of hydrocarbons. Crustal seismic reflection data along a 165‐km long Chandli‐Bundi‐Kota‐Kunjer profile of the Chambal Valley Vindhyan basin processed using common reflection surface stack method brought out new crustal features, which were missing in earlier images. A gently dipping structure of the basin is imaged with a maximum of 7.5‐km thick Proterozoic sediments, 1.5‐km thick volcanic sequence, and the granitic basement at 9.0‐km depth. The Great Boundary Thrust, a NW dipping crustal‐scale regional tectonic feature outcropping at Bundi, and a new NW dipping reflection band from 9‐ to 30‐km depth, named here as the Chambal thrust, are imaged beneath Bundi‐Kota segment. Subduction and collision are responsible for evolution of these thrusts implying horizontal crustal growth. Seismic images of compression on one side and extension on another side along with differences in the Moho characteristics and other constraints from geophysical data around Kota indicate the presence of a new tectonic boundary with a strong lateral discontinuity and strike‐slip features. The Moho topography is delineated for the first time revealing a crustal thickness ranging from 40 to 44 km. A 9‐ to 12‐km thick mafic underplating at the lower crust suggests an important postcollisional process indicating vertical crustal growth. Based on the images from the present reflection study, a geodynamic model of the region is suggested in a plate tectonic framework, which may apply to similar Paleoproterozoic collisional areas and associated basin formation.

Common-reflection-surface method in weakly anisotropic vertical transverse isotropic media

The extraction of kinematic parameters from wave propagation through traveltimes is one of the great challenges in seismic data processing. In this context, we modify the common-reflection-surface (CRS) traveltime to improve its accuracy and also interpret its parameters via paraxial ray theory in an anisotropic medium obtaining information about the wavefront curvatures measured at surface. The proposed method consists of searching for the best stacking parameters that fit the data set followed by the extraction of kinematic information from the measured waves. Numerical tests show the effectiveness of our assumptions and that the results obtained in the fitting and parameter extraction in anisotropic media achieve better accuracy than conventional CRS.

Fast and robust common-reflection-surface parameter estimation

The common-reflection-surface (CRS) method offers a stack with higher signal-to-noise ratio at the cost of a time-consuming semblance search to obtain the stacking parameters. We have developed a fast method for extracting the CRS parameters using local slope and curvature. We estimate the slope and curvature with the gradient structure tensor and quadratic structure tensor on stacked data. This is done under the assumption that a stacking velocity is already available. Our method was compared with an existing slope-based method, in which the slope is extracted from prestack data. An experiment on synthetic data shows that our method has increased robustness against noise compared with the existing method. When applied to two real data sets, our method achieves accuracy comparable with the pragmatic and full semblance searches. Our method has the advantage of being approximately two and four orders of magnitude faster than the semblance searches.

Common-reflection-surface-based prestack diffraction separation and imaging

Diffraction imaging can lead to high-resolution characterization of small-scale subsurface structures. A key step of diffraction imaging and tomography is diffraction separation and enhancement, especially in the full prestack data volume. We have considered point diffractors and developed a robust and fully data-driven workflow for prestack diffraction separation based on wavefront attributes, which are determined using the common-reflection-surface (CRS) method. In the first of two steps, we apply a zero-offset-based extrapolation operator for prestack diffraction separation, which combines the robustness and stability of the zero-offset CRS processing with enhanced resolution and improved illumination of the finite-offset CRS processing. In the second step, when the finite-offset diffracted events are separated, we apply a diffraction-based time migration velocity model building that provides high-quality diffraction velocity spectra. Applications of the new workflow to 2D/3D complex synthetic data confirm the superiority of prestack diffraction separation over the poststack method as well as the high potential of diffractions for improved time imaging.

A generalized view on normal moveout

Although in the past, in the context of stacking, traveltime moveout was only formulated in individual common-midpoint (CMP) gathers, multiparameter stacking uses normal moveout (NMO) approximations that span several neighboring CMPs. Multiparameter expressions such as the common reflection surface (CRS) or multifocusing are parameterized in terms of local slopes and curvatures of emerging wavefronts rather than effective velocities, which makes these approaches appear conceptually different from conventional velocity analysis. As a consequence, the unifying nature of multiparameter NMO is still not well-appreciated. In addition, CRS and multifocusing show distinctly different behavior in that they respond differently to the overburden heterogeneity and curvature of the target interface, and they either are or are not susceptible to moveout stretch. In our work, we seek to demystify the wavefront picture by demonstrating that the conventional and multidimensional NMO operators can conveniently be derived from the same auxiliary straight-ray geometry, either representing the optical projection or formulated in an effective replacement medium. Following the early work of de Bazelaire, we suggest a simple transformation between both domains and introduce generalized dual representations of the hyperbolic CRS, multifocusing, and the two recently introduced double-square-root expressions implicit CRS and nonhyperbolic CRS. In addition, we evaluate a generalized finite-offset NMO expression that can likewise be applied to active-source diffraction data and passive seismic events. Synthetic examples suggest unification, conveniently explain the origin of moveout stretch, and indicate that the joint use of different NMO approximations offers new insight into the character and origin of different wavefield components.

Velocity-model estimation with NIP-wave tomography inversion – A real data example

The common-reflection-surface (CRS) stack in addition to high signal-to-noise ratio stacked sections creates the curvature and local dip of a reflector. With this information, so-called kinematic wavefield attributes, it is possible to obtain a subsurface velocity model for laterally inhomogeneous media using normal-incidence-point (NIP) wave inversion. The result of CRS provides some location points on the stacked section as input for the inversion. In each iteration, dynamic ray tracing is applied along the central ray according to an input data point. With this technique, the parameter needed for forward modeling will be obtained. By updating the velocity model and minimizing the misfit between input data and the forward model parameter, it is possible to achieve a final velocity model consistent with input data. In this paper, we applied the CRS method on complex structure in the northeast of Iran, and then we performed the NIP-wave tomography inversion on this data set by means of CRS attributes. The result clearly shows the ability of NIP-wave tomography in velocity-model inversion.

A competitive comparison of multiparameter stacking operators

The classic common-midpoint (CMP) stack, which sums along offsets, suffers in challenging environments in which the acquisition is sparse. In the past, several multiparameter stacking techniques were introduced that incorporate many neighboring CMPs during summation. This increases data redundancy and reduces noise. Multiparameter methods that can be parameterized by the same wavefront attributes are multifocusing (MF), the common-reflection-surface (CRS), implicit CRS, and nonhyperbolic CRS (nCRS). The CRS-type operators use a velocity-shift mechanism to account for heterogeneity by changing the slope of the asymptote. On the other hand, MF uses a different mechanism: a shift of reference time while preserving the slope of the asymptote. We have formulated MF such that it uses the same mechanism as the CRS-type operators and compare them on a marine data set. In turn, we investigate the behavior of time-shifted versions of the CRS-type approximations. To provide a fair comparison, we use a global optimization technique, differential evolution, which allows to accurately estimate a solution without an initial guess solution. Our results indicate that the velocity-shift mechanism performs, in general, better than the one incorporating a time shift. The double-square-root operators are also less sensitive to the choice of aperture. They perform better in the case of diffractions than conventional hyperbolic CRS, and this fact is in good agreement with previous works. In our work the nCRS is of almost the same computational cost as that of conventional hyperbolic CRS, but it generally leads to a superior fit; therefore, we recommend its use in the future.

Determination of wavefront attributes by differential evolution in the presence of conflicting dips

The common-reflection surface (CRS) method represents a multidimensional stacking approach; i.e., the stacking surface is determined in the midpoint and offset directions. In the 2D case, three attributes span the stacking surface, thus requiring a three-parameter search contrary to a one-parameter search in the classic common-midpoint stack. However, CRS wavefront attributes use data redundancy in the midpoint direction as well, which makes them very useful in several seismic applications, e.g., data preconditioning, velocity model building, and migration. Contrary to previous works, we simultaneously estimate CRS attributes using differential evolution in subcubes of the 3D search space. Differential evolution is a global optimization technique that performs particularly well when the objective function is unknown. Because we apply DE for each subcube, we could find local maxima, additionally to the global maximum. Therefore, conflicting dips are recognized and can be used for the stack and subsequent CRS attribute-based processing, which has been an issue in the past. Our land data results from the Donbas Foldbelt in southeast Ukraine demonstrate that our method reduces coherent steep dipping noise and reveal more subsurface structures. Application of the CRS attributes for prestack data enhancement shows that velocity analysis can be carried out more reliably.

The use of Graphic User Interface for development of a user-friendly CRS-Stack software

The development of a user-friendly Common Reflection Surface (CRS) Stack software that has been built by implementing Graphical User Interface (GUI) is described in this paper. The original CRS-Stack software developed by WIT Consortium is compiled in the unix/linux environment, which is not a user-friendly software, so that a user must write the commands and parameters manually in a script file. Due to this limitation, the CRS-Stack become a non popular method, although applying this method is actually a promising way in order to obtain better seismic sections, which have better reflector continuity and S/N ratio. After obtaining successful results that have been tested by using several seismic data belong to oil companies in Indonesia, it comes to an idea to develop a user-friendly software in our own laboratory. Graphical User Interface (GUI) is a type of user interface that allows people to interact with computer programs in a better way. Rather than typing commands and module parameters, GUI allows the users to use computer programs in much simple and easy. Thus, GUI can transform the text-based interface into graphical icons and visual indicators. The use of complicated seismic unix shell script can be avoided. The Java Swing GUI library is used to develop this CRS-Stack GUI. Every shell script that represents each seismic process is invoked from Java environment. Besides developing interactive GUI to perform CRS-Stack processing, this CRS-Stack GUI is design to help geophysicists to manage a project with complex seismic processing procedures. The CRS-Stack GUI software is composed by input directory, operators, and output directory, which are defined as a seismic data processing workflow. The CRS-Stack processing workflow involves four steps; i.e. automatic CMP stack, initial CRS-Stack, optimized CRS-Stack, and CRS-Stack Supergather. Those operations are visualized in an informative flowchart with self explanatory system to guide the user inputting the parameter values for each operation. The knowledge of CRS-Stack processing procedure is still preserved in the software, which is easy and efficient to be learned. The software will still be developed in the future. Any new innovative seismic processing workflow will also be added into this GUI software.

Utilizing diffractions in wavefront tomography

Wavefront tomography is known to be an efficient and stable approach for velocity inversion that does not require accurate starting models and does not interact directly with the prestack data. Instead, the original data are transformed to physically meaningful wavefront attribute fields. These can be automatically estimated using local-coherence analysis by means of the common-reflection-surface (CRS) stack, which has been shown to be a powerful tool for data analysis and enhancement. In addition, the zero-offset wavefront attributes acquired during the CRS stack can be used for sophisticated subsequent processes such as wavefield characterization and separation. Whereas in previous works, wavefront tomography has been applied mainly to reflection data, resulting in smooth velocity models suitable for migration of targets with moderately complex overburden, we have emphasized using the diffracted contributions in the data for velocity inversion. By means of simple synthetic examples, we reveal the potential of diffractions for velocity inversion. On industrial field data, we suggest a joint inversion based on reflected and diffracted contributions of the measured wavefield, which confirms the general finding that diffraction-based wavefront tomography can help to increase the resolution of the velocity models. Concluding our work, we compare the quality of a reverse time migrated result using the estimated velocity model with the result based on the inversion of reflections, which reveals an improved imaging potential for a complex salt geometry.

Seismic image enhancement of mud volcano bearing complex structure by the CDS method, a case study in SE of the Caspian Sea shoreline

Improving seismic image quality in complex geological structures remains a challenge in seismic imaging. In complex media, imaging of geological structures such as the boundary of salt diapirs, faults, folding systems, overthrust zones, and unconformities are controversial and challenging tasks. Therefore, new imaging methods such as full waveform inversion, path-integral seismic imaging, reverse time migration, and the optimized common reflection surface stack methods were introduced to face these challenges. The common reflection surface stack method was used frequently to resolve some of the problems in complex structure seismic imaging. However, besides its great advantage in enhancing the quality of seismic section, it faces a problem with conflicting dips. The common reflection surface stack operator is an approximation of the reflection response of a curved interface in an inhomogeneous medium. In this study, a new strategy in the common reflection surface stack is introduced, which completely resolves the problem of conflicting dips in complex structures. Compared to the common reflection surface stack, the new stacking operator is the approximation of diffraction response of a diffraction point in depth. The kinematic wavefield attributes are defined for that diffraction point, whereas curvature of the interface is not fully considered. In the introduced strategy, there would be a stacking operator for each diffraction ray from the diffractor to the surface. Thus, the new operator gathers more energy that might get lost in imaging due to simplified operator in the other methods. The new method was applied to seismic data from a complex geological mud volcano bearing structure from south east of the Caspian Sea shoreline. This area includes numerous mud volcanoes which act as indicators of gas reservoirs. As a natural phenomenon, mud absorbs the seismic energy and deteriorates the quality of the final seismic section. Therefore, obtaining accurate image of the subsurface structures here, in the boundary portion of the mud volcano, is questionable. To overcome this problem, the new method was used to obtain a stacked section with all the possible diffraction energies. Subsequently, the stacked section underwent post stack depth migration. The final depth image proves the advantage of the new stacking operator for imaging in complex structures. Finally it could be concluded that this method could be used for imaging structures with sharp reflector truncations such as faults, diapirs, and unconformities.

Seismic data enhancement and regularization using finite offset Common Diffraction Surface (CDS) stack

The Common Reflection Surface stack is a robust method for simulating zero-offset and common-offset sections with high accuracy from multi-coverage seismic data. For simulating common-offset sections, the Common-Reflection-Surface stack method uses a hyperbolic traveltime approximation that depends on five kinematic parameters for each selected sample point of the common-offset section to be simulated. The main challenge of this method is to find a computationally efficient data-driven optimization strategy for accurately determining the five kinematic stacking parameters on which each sample of the stacked common-offset section depends. Several authors have applied multi-step strategies to obtain the optimal parameters by combining different pre-stack data configurations. Recently, other authors used one-step data-driven strategies based on a global optimization for estimating simultaneously the five parameters from multi-midpoint and multi-offset gathers. In order to increase the computational efficiency of the global optimization process, we use in this paper a reduced form of the Common-Reflection-Surface traveltime approximation that depends on only four parameters, the so-called Common Diffraction Surface traveltime approximation. By analyzing the convergence of both objective functions and the data enhancement effect after applying the two traveltime approximations to the Marmousi synthetic dataset and a real land dataset, we conclude that the Common-Diffraction-Surface approximation is more efficient within certain aperture limits and preserves at the same time a high image accuracy. The preserved image quality is also observed in a direct comparison after applying both approximations for simulating common-offset sections on noisy pre-stack data.

Implementing the CRS beam prestack depth migration with double-smearing operator within the unified Kichhoff imaging theory

The unified Kirchhoff imaging theory provides an essential theoretical foundation for understanding any Kirchhoff-type imaging methods. The local kinematic attributes are important information regarding a local coherently event in seismic dataset. We develop a double-smearing operator based common-reflection-surface (CRS) beam prestack depth migration (PSDM) based on the unified Kirchhoff imaging theory and the local kinematic attributes. Differing from the previous works based on the Hugens-curve-stacking scheme, the double-smearing operator employed in this paper is derived on the basis of the isochrones-smearing scheme defined in the unified Kirchhoff imaging theory. It provides a parallel approach to implement the CRS beam PSDM. The synthetic and real data examples demonstrate the effectiveness and robustness of the double-smearing CRS beam PSDM operator.

Effective parameters in ground roll attenuation using FO CRS stacking

Ground roll is a coherent noise in land seismic data that has high energy, high amplitude, low frequency and low velocity. It has to be attenuated in the seismic data processing as it may mask reflections in the zone of ground roll. In this study, we employed common reflection surface for finite offset (FO CRS) to attenuate the ground roll. The FO CRS stacking operator is a hyperbola; therefore, it fits the hyperbolic reflections in the prestack data. Conversely, the ground roll is linear in the common-midpoint (CMP) and common-shot (CS) gathers and can be distinguished and attenuated by the FO CRS operator. Thus, we search for the dip and curvature of the reflections in the CMP section and CS gather prior to the finite-offset section. When the algorithm is specified, the ground roll and reflections have low and high coherency values, respectively. So, any event with non-hyperbolic traveltime, like the linear traveltime ground roll can be removed.We applied the proposed method on a synthetic and an oilfield data from the west of Iran. Results showed that the FO CRS stacking method properly attenuated the ground roll. Further investigations were the effects of spatial aliasing, frequency content, random noise, ground roll dip, the range of dip and curvature scans and reflection amplitudes on ground roll attenuation by the FO CRS stacking. From mentioned parameters, spatial aliasing, frequency content, and random noise had no significant effects. On the contrary, the proposed method turned out to be strongly dependent upon ground roll dip, the range of dip and curvature scans and reflection amplitudes.

Seismic imaging of complex structures with the CO-CDS stack method

Various seismic imaging methods are introduced to resolve some of the possible ambiguities of seismic interpretation in complex structures. Reducing dependency of imaging techniques on velocity or using diffraction energy for imaging more structural details are the main topics of the imaging research. In this study, we try to improve the seismic image quality in semi-complex structures by combining the common reflection surface (CRS) method with a diffraction based scheme in the common-offset domain. Previously introduced partial CRS and common offset CRS methods exhibited reliable performance in imaging complex media. Here, we were looking for stable and efficient solutions, preserving advantages of the previous methods. Herewith, the proposed operator fits better to diffractions than to reflections. Therefore, we call it the commonoffset common diffraction surface stack (CO CDS). In a previous study, improvement of the quality of seismic image by the CRS method was achieved by combination of the CDS method with the partial CRS. This resulted in the introduction of the partial CDS. Initially, in this study, the common-offset CRS traveltime equation was modified to the common-offset CDS. The hypothetical shot reflector experiment in the CRS method was changed to shot diffraction point experiment. In the introduced operator, two wavefront curvatures, observed at receivers positions, are set equal in order to satisfy the diffraction condition. In the proposed method, we search for accurate attribute sets for each considered offset individually, and then form a new operator by four coherent attributes. Application of the common- offset CDS method on synthetic and field data shows more details of the geological structures with higher quality, while preserving continuity of reflection events. The proposed method is, however, more expensive than the partial and common offset CRS for large dataset.

Imaging seismic data in complex structures by introducing the partial diffraction surface stack method

The common reflection surface (CRS) stack method is known as a generalized stacking velocity analysis tool and was originally introduced as a data-driven method to simulate zero-offset sections. However, this method has some difficulties in imaging complex structures and low-quality data. The problem of conflicting dips is one of the drawbacks of the CRS method addressed in many studies. The common diffraction surface (CDS) method was explicitly introduced to overcome this problem. In one study, the problem was resolved by combination of the CDS method and the common offset CRS method. The method was called the common offset CDS method showed successful application on improving image quality in semi-complex media. In this study, we combined the partial CRS with the CDS to derive the partial CDS for more efficient resolve of the conflicting dips problem. In the partial CDS, thresholds in the angle spectrum were removed for full contribution of all possible dips to have volume of operators for a sample point. The aperture definition in the partial CDS is the same as in the partial CRS, where an offset and time variant aperture is used. The new method was applied on a simple synthetic data set with much diffraction points imbedded in the model. Then it was applied to a semicomplex data set to enhance the body of mud volcanoes and faults. For better comparison, it was applied to two more real data sets from a complex overthrust zone to improve the seismic quality and remove the geological ambiguities in the interpretation. In the synthetic data example, more conflicting dips were resolved than in the other methods. In all real data examples, the enhanced partial CDS data were depth-migrated to compare them with the pre-stack depth migration of partial CRS gathers. More details of the geological structures can be observed in the new results.

Improvement of seismic structural interpretation of Zagros fold-thrust belt by dip scanning in common diffraction surface imaging method

Geological interpretation and seismic imaging on data acquired from complex media, especially when accompanied by a thick layer of salt and/or anhydrate, is always a controversial task. The aim of this study is to introduce a method for seismic imaging of complex structures and study the folding scenario of the Zagros overthrust in SW Iran based on the improved seismic image processed by the proposed method. A diffraction based version of the common reflection surface stack method, called the common diffraction surface (CDS), was selected to enhance quality of seismic image from the Zagros fold-thrust belt. The 2D CDS method was also developed here to 3D partial CDS. Consequently, three sets of 2D and a set of 3D seismic data were processed with the conventional Kirchhoff prestack time migration and the partial common diffraction surface methods. Geological models released in previous studies of the Zagros overthrust were used as the base model of interpretation. Structural interpretation on seismic sections with new method was in accordance with previous geological models and improved in some parts where the new method could enhance quality of the seismic image. Seismic structural interpretation shows the inner part of the belt was subjected to folding, uplift and erosion. This mechanism constituted a resistant mass in the Dezful Embayment in front of the SW moving thrust and folds. This resistant mass formed tightly folded or thrusted and highly shortened structures in the Izeh zone and High Zagros area. In the oil rich zone of the Dezful Embayment, the thick evaporate—rich Gachsaran Formation, decouples the folding above it from the folding below, making seismic imaging of potential traps beneath the detachment horizons extremely difficult.

Seismo-stratigraphic evidences for deep base level control on middle to late Pleistocene drift evolution and mass wasting along southern Levant continental slope (Eastern Mediterranean)

Since early Pliocene, a counterclockwise surface gyre transported Nile derived silt and clay northeastwards along the Levant coast, where a basinward prograding plastered drift emerged. Based on high-resolution seismic reflection data we develop a middle to late Pleistocene sequence stratigraphic scheme for this plastered drift. For creating stacked sections of the seismic data we used the common reflection surface (CRS) stack technology which enhanced lateral reflection continuity and visibility of deep reflections. The shelf comprises stratigraphic sequences which show classical, systems tract like stacking patterns of sea level controlled sequences such as offlapping forced regression deposits or diachronous ravinement surfaces which formed during base level rise. On the slope, base level was periodically located well below the wave base and thus rather controlled by hydrodynamics, presumably by high-velocity contour currents. Hence, the term ‘deep base level’ is introduced. The deep base level controlled especially down and backstepping slope deposits. This example shows that care has to be taken when interpreting subsurface data containing typical systems tract like seismic sequences, since such geometries do not necessarily imply shallow water deposition of the sediments. A chronostratigraphic analysis based on the seismic stratigraphy indicates that base level fluctuations were related to eccentricity driven glacio-eustatic fluctuations. Periodic mass wasting, facilitated by foreset over-steepening and possibly triggered by salt tectonics or erosion by the contour current occurred during late base level fall or early base level rise.

Common-reflection-point time migration

Since the early days of seismic processing, time migration has proven to be a valuable tool for a number of imaging purposes. Main motivations for its widespread use include robustness with respect to velocity errors, as well as fast turnaround and low computation costs. In areas of complex geology, in which it has well-known limitations, time migration can still be of value by providing first images and also attributes, which can be of much help in further, more comprehensive depth migration. Time migration is a very close process to common-midpoint (CMP) stacking and, more recently, to zero-offset commonreflection- surface (CRS) stacking. In fact, Kirchhoff time migration operators can be readily formulated in terms of CRS parameters. In the nineties, several studies have shown advantages in the use of common-reflection-point (CRP) traveltimes to replace conventional CMP traveltimes for a number of stacking and migration purposes. In this paper, we follow that trend and introduce a Kirchhoff-type prestack time migration and velocity analysis algorithm, referred to as CRP time migration. The algorithm is based on a CRP operator together with optimal apertures, both computed with the help of CRS parameters. A field-data example indicates the potential of the proposed technique.

Passive seismic source localization via common-reflection-surface attributes

The common-reflection-surface (CRS) stack can be viewed as a physically justified extension of the classical common-midpoint (CMP) stack, utilizing redundant information not only in a single, but in several neighboring CMP gathers. The zero-offset CRS moveout is parameterized in terms of kinematic attributes, which utilize reciprocity and raypath symmetries to describe the two-way process of the actual wave propagation in active seismic experiments by the propagation of auxiliary one-way wavefronts. For the diffraction case, only the attributes of a single one-way wavefront, originating from the diffractor are sufficient to explain the traveltime differences observed at the surface. While paraxial ray theory gives rise to a second-order approximation of the CRS traveltime, many higher-order approximations were subsequently introduced either by squaring the second-order expression or by employing principles of optics and geometry. It was recently discovered that all of these higher-order operators can be formulated either for the optical projection or in an auxiliary medium of a constant effective velocity. Utilizing this duality and the one-way nature of the CRS parameters, we present a simple data-driven stacking scheme that allows for the estimation of the a priori unknown excitation time of a passive seismic source. In addition, we demonstrate with a simple data example that the output of the suggested workflow can directly be used for subsequent focusing-based normal-incidence-point (NIP) tomography, leading to a reliable localization in depth.