scholarly journals Reverse time migration (RTM) imaging of iron-oxide deposits in the Ludvika mining area, Sweden

2020 ◽  
Author(s):  
Yinshuai Ding ◽  
Alireza Malehmir
Keyword(s):  
Iron Oxide ◽  
Large Scale ◽  
Mining Area ◽  
Mineral Deposits ◽  
Great Level ◽  
Reverse Time ◽  
Reverse Time Migration ◽  
Imaging Algorithm ◽  
Time Migration ◽  
Seismic Methods

Abstract. To discover or delineate mineral deposits and other geological features such as faults and lithological boundaries in their host rocks, seismic methods are a qualified choice, given their resolution power at depth. One major goal for seismic methods is to produce a reliable image of the subsurface given the typical discontinuous geology in crystalline environment with low signal-to-noise ratio. In this study, we investigate the usefulness of reverse time migration (RTM) imaging algorithm in hardrock environment by applying it to a legacy 2D dataset, which was acquired in the Ludvika mining area of central Sweden. We provide a how-to solution for applications of RTM in future and similar datasets. When using the RTM imaging technique properly, it is possible to obtain high-fidelity seismic images of the subsurface. Due to good amplitude preservation in the RTM image, the imaged reflectors provide indications to infer their geological origin. Aside from the chosen seismic imaging algorithm, we illustrate that two other important factors for successful RTM imaging workflows are the suitable acquisition and careful data pre-processing. Exemplified with the Ludvika legacy data, the RTM method allows imaging the iron-oxide deposits at a great level of detail down to 1200 m depth as shown from previous studies. It also provides much-improved images of the lithological contacts and crosscutting features relative to the mineralized sheets. Some of the imaged crosscutting features are considered to be crucial when interpreting large-scale geological structures of the site and the likely disappearance of mineralization at depth. The RTM imaging workflows have the potential to be used on hardrock seismic data and for deep targeting mineral deposits, a key message we would like to deliver in this article.

scholarly journals Reverse time migration (RTM) imaging of iron oxide deposits in the Ludvika mining area, Sweden

Solid Earth ◽  
2021 ◽  
Vol 12 (8) ◽  
pp. 1707-1718
Author(s):  
Yinshuai Ding ◽  
Alireza Malehmir
Keyword(s):  
Iron Oxide ◽  
Large Scale ◽  
Random Noise ◽  
Mining Area ◽  
Mineral Deposits ◽  
Reverse Time ◽  
Reverse Time Migration ◽  
Near Surface ◽  
Time Migration ◽  
Seismic Methods

Abstract. To discover or delineate mineral deposits and other geological features such as faults and lithological boundaries in their host rocks, seismic methods are preferred for imaging the targets at great depth. One major goal for seismic methods is to produce a reliable image of the reflectors underground given the typical discontinuous geology in crystalline environments with low signal-to-noise ratios. In this study, we investigate the usefulness of the reverse time migration (RTM) imaging algorithm in hardrock environments by applying it to a 2D dataset, which was acquired in the Ludvika mining area of central Sweden. We provide a how-to solution for applications of RTM in future and similar datasets. When using the RTM imaging technique properly, it is possible to obtain high-fidelity seismic images of the subsurface. Due to good amplitude preservation in the RTM image, the imaged reflectors provide indications to infer their geological origin. In order to obtain a reliable RTM image, we performed a detailed data pre-processing flow to deal with random noise, near-surface effects, and irregular receiver and source spacing, which can downgrade the final image if ignored. Exemplified with the Ludvika data, the resultant RTM image not only delineates the iron oxide deposits down to 1200 m depth as shown from previous studies, but also provides a better inferred ending of sheet-like mineralization. Additionally, the RTM image provides much-improved reflection of the dike and crosscutting features relative to the mineralized sheets when compared to the images produced by Kirchhoff migration in the previous studies. Two of the imaged crosscutting features are considered to be crucial when interpreting large-scale geological structures at the site and the likely disappearance of mineralization at depth. Using a field dataset acquired in hardrock environment, we demonstrate the usefulness of RTM imaging workflows for deep targeting mineral deposits.

Enhanced prestack depth imaging of wide-azimuth data from the Gulf of Mexico: A case history

Geophysics ◽  
2011 ◽  
Vol 76 (5) ◽  
pp. WB79-WB86 ◽  
Author(s):  
Xuening Ma ◽  
Bin Wang ◽  
Cristina Reta-Tang ◽  
Wilfred Whiteside ◽  
Zhiming Li
Keyword(s):  
Image Quality ◽  
Gulf Of Mexico ◽  
Large Scale ◽  
Velocity Model ◽  
Reverse Time ◽  
Reverse Time Migration ◽  
Delayed Imaging ◽  
Data Set ◽  
Depth Imaging ◽  
Time Migration

We present a case study of enhanced imaging of wide-azimuth data from the Gulf of Mexico utilizing recent technologies; and we discuss the resulting improvements in image quality, especially in subsalt areas, relative to previous results. The input seismic data sets are taken from many large-scale wide-azimuth surveys and conventional narrow-azimuth surveys located in the Mississippi Canyon and Atwater Valley areas. In the course of developing the enhanced wide azimuth processing flow, the following three key steps are found to have the most impact on improving subsalt imaging: (1) 3D true azimuth surface-related multiple elimination (SRME) to remove multiple energy, in particular, complex multiples beneath salt; (2) reverse-time migration (RTM) based delayed imaging time (DIT) scans to update the complex subsalt velocity model; and (3) tilted transverse isotropic (TTI) RTM to improve image quality. Our research focuses on the depth imaging aspects of the project, with particular emphasis on the application of the DIT scanning technique. The DIT-scan technique further improves the accuracy of the subsalt velocity model after conventional ray-based subsalt tomography has been performed. We also demonstrate the uplift obtained by acquiring a wide-azimuth data set relative to a standard narrow-azimuth data set, and how orthogonal wide-azimuth is able to enhance the subsalt illumination.

Fast image-domain target-oriented least-squares reverse time migration

Geophysics ◽  
2018 ◽  
Vol 83 (6) ◽  
pp. A81-A86 ◽  
Author(s):  
Zeyu Zhao ◽  
Mrinal K. Sen
Keyword(s):  
Plane Wave ◽  
Least Squares ◽  
Large Scale ◽  
Green's Functions ◽  
Green’S Functions ◽  
Hessian Matrix ◽  
Reverse Time ◽  
Reverse Time Migration ◽  
Image Domain ◽  
Time Migration

We have developed a fast image-domain target-oriented least-squares reverse time migration (LSRTM) method based on applying the inverse or pseudoinverse of a target-oriented Hessian matrix to a migrated image. The image and the target-oriented Hessian matrix are constructed using plane-wave Green’s functions that are computed by solving the two-way wave equation. Because the number of required plane-wave Green’s functions is small, the proposed method is highly efficient. We exploit the sparsity of the Hessian matrix by computing only a couple of off-diagonal terms for the target-oriented Hessian, which further improves the computational efficiency. We examined the proposed LSRTM method using the 2D Marmousi model. We demonstrated that our method correctly recovers the reflectivity model, and the retrieved results have more balanced illumination and higher spatial resolution than traditional images. Because of the low cost of computing the target-oriented Hessian matrix, the proposed method has the potential to be applied to large-scale problems.

scholarly journals A study of infrasonic anisotropy and multipathing in the atmosphere using seismic networks

2013 ◽  
Vol 371 (1984) ◽  
pp. 20110542 ◽  
Author(s):  
Michael A. H. Hedlin ◽  
Kristoffer T. Walker
Keyword(s):  
Gravity Waves ◽  
Large Scale ◽  
Three Dimensional ◽  
Atmospheric Model ◽  
Internal Gravity Waves ◽  
Reverse Time ◽  
Reverse Time Migration ◽  
Layer Cake ◽  
Time Migration ◽  
Seismic Networks

We discuss the use of reverse time migration (RTM) with dense seismic networks for the detection and location of sources of atmospheric infrasound. Seismometers measure the response of the Earth's surface to infrasound through acoustic-to-seismic coupling. RTM has recently been applied to data from the USArray network to create a catalogue of infrasonic sources in the western US. Specifically, several hundred sources were detected in 2007–2008, many of which were not observed by regional infrasonic arrays. The influence of the east–west stratospheric zonal winds is clearly seen in the seismic data with most detections made downwind of the source. We study this large-scale anisotropy of infrasonic propagation, using a winter and summer source in Idaho. The bandpass-filtered (1–5 Hz) seismic waveforms reveal in detail the two-dimensional spread of the infrasonic wavefield across the Earth's surface within approximately 800 km of the source. Using three-dimensional ray tracing, we find that the stratospheric winds above 30 km altitude in the ground-to-space (G2S) atmospheric model explain well the observed anisotropy pattern. We also analyse infrasound from well-constrained explosions in northern Utah with a denser IRIS PASSCAL seismic network. The standard G2S model correctly predicts the anisotropy of the stratospheric duct, but it incorrectly predicts the dimensions of the shadow zones in the downwind direction. We show that the inclusion of finer-scale structure owing to internal gravity waves infills the shadow zones and predicts the observed time durations of the signals. From the success of this method in predicting the observations, we propose that multipathing owing to fine scale, layer-cake structure is the primary mechanism governing propagation for frequencies above approximately 1 Hz and infer that stochastic approaches incorporating internal gravity waves are a useful improvement to the standard G2S model for infrasonic propagation modelling.

CuQ-RTM: A CUDA-based code package for stable and efficient Q-compensated reverse time migration

Geophysics ◽  
2019 ◽  
Vol 84 (1) ◽  
pp. F1-F15 ◽  
Author(s):  
Yufeng Wang ◽  
Hui Zhou ◽  
Xuebin Zhao ◽  
Qingchen Zhang ◽  
Poru Zhao ◽  
...  
Keyword(s):  
Large Scale ◽  
Gpu Computing ◽  
Graphics Processing Unit ◽  
Processing Unit ◽  
Program Optimization ◽  
Adaptive Stabilization ◽  
Reverse Time ◽  
Reverse Time Migration ◽  
Data Set ◽  
Time Migration

Reverse time migration (RTM) in attenuating media should take absorption and dispersion effects into consideration. The latest proposed viscoacoustic wave equation with decoupled fractional Laplacians facilitates separate amplitude compensation and phase correction in [Formula: see text]-compensated RTM ([Formula: see text]-RTM). However, intensive computation and enormous storage requirements of [Formula: see text]-RTM prevent it from being extended into practical application, especially for large-scale 2D or 3D cases. The emerging graphics processing unit (GPU) computing technology, built around a scalable array of multithreaded streaming multiprocessors, presents an opportunity for greatly accelerating [Formula: see text]-RTM by appropriately exploiting GPUs architectural characteristics. We have developed the cu[Formula: see text]-RTM, a CUDA-based code package that implements [Formula: see text]-RTM based on a set of stable and efficient strategies, such as streamed CUDA fast Fourier transform, checkpointing-assisted time-reversal reconstruction, and adaptive stabilization. The cu[Formula: see text]-RTM code package can run in a multilevel parallelism fashion, either synchronously or asynchronously, to take advantages of all the CPUs and GPUs available, while maintaining impressively good stability and flexibility. We mainly outline the architecture of the cu[Formula: see text]-RTM code package and some program optimization schemes. The speedup ratio on a single GeForce GTX760 GPU card relative to a single core of Intel Core i5-4460 CPU can reach greater than 80 in a large-scale simulation. The strong scaling property of multi-GPU parallelism is demonstrated by performing [Formula: see text]-RTM on a Marmousi model with one to six GPU(s) involved. Finally, we further verified the feasibility and efficiency of the cu[Formula: see text]-RTM on a field data set.

3D coupled acoustic-elastic migration with topography and bathymetry based on spectral-element and adjoint methods

Geophysics ◽  
2013 ◽  
Vol 78 (4) ◽  
pp. S193-S202 ◽  
Author(s):  
Yang Luo ◽  
Jeroen Tromp ◽  
Bertrand Denel ◽  
Henri Calandra
Keyword(s):  
Surface Topography ◽  
Large Scale ◽  
Mass Density ◽  
Spectral Element ◽  
Wave Impedance ◽  
P Wave ◽  
Reverse Time ◽  
Reverse Time Migration ◽  
Wave Speeds ◽  
Time Migration

In the context of the adjoint method, we considered 3D coupled acoustic-elastic migration in the presence of surface topography and/or bathymetry. Isotropic elastic imaging involves three primary kernels, related to mass density and shear and bulk moduli, and various secondary kernels, for example, related to P-wave impedance and compressional and shear-wave speeds. Similar to reverse-time migration, these kernels reflect the constructive interference between a forward wavefield generated by active sources and an adjoint wavefield triggered by simultaneously back propagating recorded reflections from all receivers. Forward and adjoint wavefields were simulated using a spectral-element method, which, due to its weak nature, captures free-surface topography in land surveys and bathymetry in marine acquisition. To avoid storing the entire 3D forward wavefield, required for calculating its interaction with the adjoint wavefield, we only saved information on domain boundaries and reconstructed the forward wavefield while simulating the adjoint wavefield. Their interactions were calculated and integrated on the fly, thereby eliminating storage issues but doubling memory and CPU requirements. Our 3D images confirmed a previous conclusion based on 2D simulations, namely, that the impedance kernel best highlights reflectors, whereas wave-speed kernels constrain large-scale structures, i.e., the background model.

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