Prestack Depth Migration Technique Research Articles

Tomographic imaging of South Rewa basin, Central India: Implications of Gondwana rifting and Late Cretaceous volcanism

We have imaged thick (3.0–5.0 km) sub-trappean Gondwana sediments deposited in a typical rift-environment of the south Rewa basin in Central India masked by the Deccan basalts. The basalts intrude through the basin forming several dykes, sills, and other intrusions along with large-scale undulations of the basement showing complex geology and tectonic settings due to Late Cretaceous volcanism (∼65 Ma). To delineate complex subsurface geological structures and understand the tectonic settings, we use long-offset seismic reflection data along the N-S trending 127 km Kuvari-Shahdol profile of the basin. The conventional stack and pre-stack time migration techniques fail to image the complex subsurface structures dominated by steeply dipping faults. The steeply dipping faults with small-scale structures are influenced by strong lateral and vertical velocity variations that cause problems in imaging the basin. Hence, a robust tomographic inversion with pre-stack depth migration technique is adopted to image fine-scale subtle subsurface geological structures with smooth velocity variations. The tomographic velocity model and pre-stack depth migration seismic image could decipher basaltic trap thickness, numerous dyke intrusions, alternate horsts and grabens with deposition of thick hydrocarbon-bearing sub-trappean Gondwana rocks along with the basement configuration. The deep basinal faults with highly distorted basement structures represent the intense tectonic activity of this Gondwana rift-basin. The deep-seated hydrocarbon reservoir is discovered with an excellent trapping mechanism forming both pre-rift and syn-rift settings of the rift-basin. The seismic image is further constrained and corroborated by the inversion of residual Bouguer gravity anomaly data to obtain corresponding density model derived from tomographic velocity model. The large basement faults, horsts and grabens, several intrusives like dyke, sill, laccolith, and thick sub-trappean Gondwana formations with Deccan trap cover indicate complex geology and tectonic settings of south Rewa basin forming the Late Cretaceous Volcanic Province of India.

Seismic depth-domain stratigraphic classification of the Golan Heights, central Dead Sea Fault

A set of twenty five 2-D seismic profiles acquired over the Golan Heights basaltic plateau, central Dead Sea Fault segment, was processed and analyzed in the depth domain. The data were processed by the Pre-Stack Depth Migration techniques and, despite the thick basaltic layer entirely covering the plateau, shows surprisingly good quality. The study presents stratigraphic identification of eleven seismic markers recognized on the output depth-domain sections and their correlation with the adjacent Syrian, Jordanian and Israeli stratigraphic columns. Based on this regional correlation, the deep-seated structure and stratigraphic column underlying the extensive basaltic cover are addressed through structural mapping and isopach calculations, as well as through compilation of regional geological cross-sections. Results of the depth-domain seismic interpretation suggest that the Golan Heights covers a structural depression in which more than 8500 m of Late Proterozoic to Neogene sedimentary succession has accumulated, amid the Jordanian Highlands and the Mt. Hermon Anticline. The Infracambrian–Paleozoic succession attains a thickness of 3000–3500 m, while as much as 1500 m of this figure is attributed to the Late Proterozoic Saramuj Formation. The Mesozoic succession, outlined by the significant northward and north-western thickening of the Triassic and Jurassic successions, attains a cumulative thickness of 5 km in the Northern Golan. The Senonian–Cenozoic succession outlines the syncline nature of the Golan Plateau, attaining a thickness of 1.5–2 km at the central parts of the plateau. The estimated thickness of the Plio–Pleistocene basalt flows that cover the study area locally exceeds 1000 m. Two fault strands of the Dead Sea Fault System are recognized in the subsurface of the plateau: the Sheikh-Ali and Shamir Faults. The strands are interpreted beneath the basalt cover, extending into the plateau at a considerable distance from their surface expression next to the Arabian–Sinai plate boundary frontier, exhibiting various styles of deformation.

Deep structures and seismic stratigraphy of the Egyptian continental margin from multichannel seismic data

Abstract Regional multichannel seismic reflection (MCS) profiles across the Egyptian continental slope, offshore the Nile delta, were recorded during the MEDISIS survey (conducted in 2002 on board the R/V Nadir ). The results of this survey allow an interpretation of the overall structure and evolution of this passive continental margin. The MCS data were processed using an amplitude preserving pre-stack depth migration technique, which has the advantage of providing a quantitative, and geometrically correct, image of seismic horizons. Well-defined reflecting events allow the identification of three main seismic units. The upper unit (a 7 km thick) is interpreted as the post-rift sedimentary cover of the margin; it includes an undisturbed Middle Cretaceous to Upper Miocene sedimentary pile, covered by thick Messinian (latest Miocene) salt-rich layers and by Pliocene to Quaternary sediments, locally intensively deformed by gravity tectonics. The underlying intermediate acoustic unit (6 km thick on average) is interpreted as the Mesozoic syn-rift sedimentary cover of the margin; the end of the last rifting event is marked by a strong angular unconformity, tentatively of Aptian age. The lower unit may correspond to the thinned continental crust of Africa (12 km thick on average in the study area) and its pre-rift cover. Its base is identified by strong, discontinuous reflector packages about 23–25 km below sea floor, interpreted as indicative of the Moho.

Efficient 3D wave-equation migration using virtual planar sources

Full-volume seismic imaging is essential for a sound interpretation of structurally complex geologies. Prestack depth imaging is the most appropriate tool for such imaging, but it requires a precise and often complex velocity model. In such situations, 3D Kirchhoff prestack depth migration can be quite expensive. On the other hand, a wavefield approach, although generally tremendously expensive, is not affected by the complexity of the velocity model. We propose an affordable 3-D wavefield prestack depth-migration technique. It is designed for marine surveys for which the source-receiver azimuth is approximately constant. The technique applies a plane-wave migration algorithm to time-shifted data — quite a surprising approach when we realize that marine surveys do not allow the synthesis of genuine plane-wave data. Additionally, the imaging principle has to be modified to give results consistent with shot-record migration. Our technique also produces image gathers that allow an update of the velocity model by means of migration velocity analysis. Results from synthetics and conventional marine data demonstrate the effectiveness of the method.

3-D Kirchhoff Migration of GPR Data to Image the Inside of a Stone Pagoda

We have chosen the GPR method for investigating the inner structure of a stone pagoda in a non-destructive way. The selection of a suitable source frequency of the GPR antenna is the key because the main frequency of its pulse controls the resolution and the depth of the investigation. Through theoretical consideration and numerical simulation, we found that 500 to 800 MHz is suitable for a field model with a foundation part of 3 to 4 m. To image the inner structure we selected 3-D Kirchhoff prestack depth migration technique used in seismic processing. We have used the modified migration algorithm for the source and receiver configurations of common offset GPR data. To verify the scheme, we calculated the synthetic data using the 3-D FDTD algorithm and applied the migration technique to it. Through these experiments, we confirmed that the 3-D Kirchhoff prestack depth migration technique is a very powerful tool to image the inside of a stone pagoda with high resolution. We have also applied the technique to the field data of the foundation of a five-story stone pagoda at Jeongnim temple site in Buyeo City, Korea. Based on the 3-D migrated images, we inferred that the structure of the foundation of this pagoda seemed to be preserved quite well and the thickness of the outer wall was about 0.5 m.

Migração sísmica 2-D pré-empilhamento em profundidade com operadores de extrapolação "split-step"

Three 2D prestack depth migration techniques using split-step extrapolation operators were developed and tested on seismic data sorted into common shot gathers. In the first method, which we name simultaneous split-step migration (SS-S), the migration procedure is carried out simultaneously for the sources and receivers. The recorded receiver data are depropagated in depth and the source wavefield is downward propagated using the split-step operators for both. The final depth section is achieved by summing all the frequencies of interest after the correlation of the propagated and depropagated wavefields, for each depth level and by the sum of all migrated shot gathers. To decrease the computational time of the SS-S method, we can calculate the source wavefield's through a finite difference solution of the eikonal equation. This second method we call the hybrid split-step migration method (SS-H). In the third migration method, we combine the SS-S with the PSPI method. In this case the wavefields are depropagated using split-step operators for different velocities and then interpolated as in the PSPI method. We called this method PSPI-SS. The choice of the split-step operator for migration is mainly due to its easy implementation, high accuracy and robustness even in situations with very strong lateral velocity variation. The results we present in this work were obtained using the Marmousi data and also the SEG-EAGE salt model, which present very high geologic complexity. The results obtained with the three differentes methods were compared and all show satisfactory images.

Prestack depth imaging via model-independent stacking

Most seismic reflection imaging methods are confronted with the difficulty of accurately knowing input velocity information. To eliminate this, we develop a special prestack depth migration technique which avoids the necessity of constructing a macro-velocity model. It is based upon the weighted Kirchhoff-type migration formula expressed in terms of model-independent stacking velocity and arrival angle. This formula is applied to synthetic sub-basaltic data. Numerical results show that the method can be used to successfully image beneath basalts.