Interpretation Of Seismic Reflection Data Research Articles

INTERPRETASI DATA SEISMIK REFLEKSI : PICKING HORIZON DAN PICKING FAULT

Seismic method practicum has been carried out with the title "Interpretation of reflection seismic data: picking horizon and picking fault". The seismic method is a geophysical method that is often used in imaging the subsurface conditions of the earth. The purpose of this practicum is to find out how to do picking horizon and picking fault. Picking horizon and picking faults are done with petrel software. Picking Horizon is a method that is carried out by making a horizon line on a continuous layer on a seismic cross section. For picking horizon, petrel software is used. From these data it is known that there are 3 horizons (layers). Fault picking is carried out simultaneously with seismic horizon picking. Fault picking is carried out starting from a clear shift in the horizon and continuing to the vertical shift zone. For picking faults, petrel software is used. From these data it is known that there are 4 faults (faults).

Implications of Timanian thrust systems in the Barents Sea and Svalbard on using paleontological constraints for plate tectonics reconstructions.

The Svalbard Archipelago is commonly believed to have been located at comparable latitude and, possibly, to have been attached to Laurentia in the early Paleozoic (500-420 Ma) based on trilobite assemblage similarities. Trilobite assemblage differences and lack of mixing between Laurentia-Svalbard and Baltica were further used to propose that these continents were separated by the Iapetus Ocean at that time. However, recent structural correlation of Timanian (650-550 Ma) thrust systems throughout the Barents Sea show that Svalbard was already attached to Baltica in the latest Neoproterozoic and remained so during the Phanerozoic. The present study presents a new interpretation of seismic reflection data from the DISKOS database, which were tied to nearby exploration wells. The study uses recently acquired knowledge of the seismic facies of intensely deformed pre-Caledonian rocks and principles of sequence stratigraphy to interpret the data. The present study reconciles the proximity of Svalbard and Laurentia with the early accretion of Svalbard to Baltica in the latest Neoproterozoic. It also describes the influence of Timanian thrust systems on paleoenvironments and possible effects on trilobite assemblages, e.g., the lack of mixing between those of Laurentia-Svalbard and Baltica. The results suggest that paleontological constraints are robust markers to discuss continent amalgamation but should be considered with greater care when discussing continent separation since other factors, such as major thrust systems, may create major, linear, topographical boundaries, which may act as major faunal barriers within a single tectonic plate. Other factors to consider include paleoclimatic belts.

The Langeland Fault System unravelled: Quaternary fault reactivation along an elevated basement block between the North German and Norwegian–Danish basins

The reactivation of faults and possible impact on barrier integrity marks a critical aspect for investigations on subsurface usage capabilities. Glacial isostatic adjustments, originating from repeated Quaternary glaciations of northern Europe, cause tectonic stresses on pre‐existing fault systems and structural elements of the North German and Norwegian–Danish basins. Notably, our current understanding of the dynamics and scales of glacially induced fault reactivation is rather limited. A high‐resolution 2D seismic data set recently acquired offshore northeastern Langeland Island allows the investigation of a fault and graben system termed the Langeland Fault System. Seismo‐stratigraphic interpretation of reflection seismic data in combination with diffraction imaging unravels the spatial character of the Langeland Fault System along an elevated basement block of the Ringkøbing–Fyn High. In combination with sediment echosounder data, the data set helps to visualize the continuation of deep‐rooted faults up to the sea floor. Initial Mesozoic faulting occurred during the Triassic. Late Cretaceous inversion reactivated a basement fault flanking the southern border of the elevated basement block of the Ringkøbing–Fyn High while inversion is absent in the Langeland Fault System. Here, normal faulting occurred in the Maastrichtian–Danian. We show that a glacial or postglacial fault reactivation occurred within the Langeland Fault System, as evident by the propagation of the faults from the deeper subsurface up to the sea floor, dissecting glacial and postglacial successions. Our findings suggest that the Langeland Fault System was reactivated over a length scale of a minimum of 8.5 km. We discuss the causes for this Quaternary fault reactivations in the context of glacially induced faulting and the present‐day stress field. The combination of imaging techniques with different penetration depths and vertical resolution used in this study is rarely realized in the hinterland. It can therefore be speculated that many more inherited, deep‐rooted faults were reactivated in Pleistocene glaciated regions.

Cross-scale rockmass characterization by high resolution seismic imaging around tunnels

Reflection seismic surveys are relevant to the detailed characterisation of crystalline bedrock. Relatively small-scale features, even single fractures, can demonstrably be detected. Integrated analysis and modelling of geological, hydrogeological and geophysical data is instrumental in the interpretation of reflection seismic data. This requires the inference of the nature of the reflectors, e.g. lithological contacts or deformation zones and resolving the orientation ambiguity of the reflectors. Brittle deformation zones and large fractures may be heterogeneous in their detailed structure, making their characterization a challenging task. Several examples of structure characterization ahead and around tunnels are presented, with focus on the safety assessment for engineering and mining applications. Seismic imaging techniques adapted for tunnels and galleries are presented with examples from high resolution seismic surveys carried out at ONKALO (Finland) and Äspö HRL (Sweden). Studies performed over a span of several years demonstrate that large fractures identified initially through geological mapping, can also be found, positioned and characterized by seismics at the small scale of tunnels and/or boreholes. We show that reflection seismic surveys are relevant to the detailed characterization of crystalline bedrock. The detection of some distinctive features, even large-scale, can be uncertain if the survey layout is spatially constrained. Combinations of borehole and tunnel measurements using measuring arrays with diverse orientations helped reduce the location ambiguities and are recommended to be used in mining and tunneling rock characterization surveys wherever possible.

Deformation features and tectonic transfer of the Gumubiezi Fault in the northwestern margin of Tarim Basin, NW China

Through field geologic survey, fine interpretation of seismic reflection data and analysis of well drilling data, the differential deformation, tectonic transfer and controlling factors of the differential deformation of the Gumubiezi Fault (GF) from east to west have been studied systematically. The study shows that GF started to move southward as a compressive decollement along the Miocene gypsum-bearing mudstone layer in the Jidike Formation at the Early Quaternary and thrust out of the ground surface at the northern margin of the Wensu Uplift, and the Gumubiezi anticline formed on the hanging wall of the GF. The displacement of the GF decreases gradually from 1.21 km in the east AA′ transect to 0.39 km in the west CC′ transect, and completely disappears in the west of the Gumubiezi anticline. One part of the displacement of the GF is converted into the forward thrust, and another part is absorbed by Gumubiezi anticline. The formation of the GF is related to the gypsum-bearing mudstone layer in the Jidike Formation and barrier of the Wensu Uplift. The differential deformation of the GF from east to west is controlled by the development difference of gypsum-bearing mudstone layer in the Jidike Formation. In the east part, gypsum-bearing mudstone layer in the Jidike Formation is thicker, the deformation of the duplex structure in the north of the profile transferred to the basin along gypsum-bearing mudstone layer; to the west of the Gumubiezi structural belt (GSB), the gypsum-bearing mudstone layer in Jidike Formation decreases in thickness, and the transfer quantity of deformation of the duplex structure along the gypsum-bearing mudstone layer to the basin gradually reduces. In contrast, on the west DD′ profile, the gypsum-bearing mudstone is not developed, the deformation of the deep duplex structure cannot be transferred along the Jidike Formation into the basin, the deep thrust fault broke to the surface and the GF disappeared completely. The displacement of the GF to the west eventually disappeared, because the lateral ramp acts as the transitional fault between east and west part of GSB.

Basin analysis using seismic interpretation as a tool to examine the extent of a basin ore ‘play’

Stratiform and stratabound base metal ores typically form in sedimentary basins during the overall rifting process with mineralising fluids transported along the growing normal faults. Understanding the detailed structural evolution, i.e. the timing, the growth and the extent of the faults, and the distribution and thickness of the syn-faulting sedimentary packages, is critical for focusing exploration efforts. In this paper, we describe how seismic interpretation and basin analysis techniques can help to do this. We assess the potential for Pb-Zn mineralisation within the Northumberland Trough, northern England, in the context of the wider Early Carboniferous basin evolution and the associated base metal ores. Through structural interpretation of seismic reflection data, we consider the detailed evolution of the fault geometries and sedimentation in time and space, to show the extent and distribution of the Early Carboniferous faulting and growth packages at depth in the study area. We conclude that basin evolution and structural framework in northern England is very similar to that associated with the significant Pb-Zn mineralisation in Ireland. We suggest a refined model for the Carboniferous evolution of this part of the basin. The study demonstrates how the techniques of basin analysis can be a used in ore exploration to establish whether the basic structural and sedimentary framework exists to enable mineralisation. In addition to assessing the general potential of base metal mineralisation, a more precise identification of potentially suitable areas for further investigation can be made. The seismic data and basin analysis approach used in this paper and exemplified through the Northumberland case should be directly applicable to any basin ore 'play' associated with rifting and/or sedimentation. The added, significant advantage of this method is the ability to assess the 3D fault geometries, including fault linkage and growth in space and time, and the associated sedimentation – an unachievable outcome if relying solely on other geophysical and geological data traditionally used in regional ore exploration.

Geochemical Characterization and Thermal Maturation of Cerrejón Formation: Implications for the Petroleum System in the Ranchería Sub-Basin, Colombia

The Upper Paleocene Cerrejón Formation is a great source of coal in Colombia. The northeastern part of the Ranchería Sub-Basin sees the most intense mining activity. As a consequence, all geological studies have been concentrated on this region. Consequently, neither the distribution of the Cerrejón Formation, nor the quality and quantity of organic matter in the rest of the sub-basin is clear. In this study, we analyzed new geochemical data from Rock–Eval pyrolysis analyses and vitrinite reflectance using core samples from the ANH-CAÑABOBA-1 and ANH-CARRETALITO-1 wells. Based on this information, it was possible to classify the geochemical characteristics of the Cerrejón Formation as a source rock, particularly in the central area of the sub-basin, which had not been extensively studied before. Additionally, based on the interpretation of seismic reflection data, the numerical burial history models were reconstructed using PetroMod software, in order to understand the evolution of the petroleum system in the sub-basin. The models were calibrated with the data of maximum pyrolysis temperature (Tmax), vitrinite reflectance (%Ro), and bottom hole temperature (BHT). We infer the potential times of the generation and expulsion of hydrocarbon from the source rock.

Transition from amagmatic to volcanic margin: Mantle exhumation in the Vøring Basin before the Icelandic plume influence

The outer Vøring Basin, Norwegian Sea, is an abnormally deep and distal part of the Norwegian passive margin, known as “magma-rich”. Yet, the lastest borehole drilled in its northernmost part led to a drastic change in the interpretation of seismic reflection data. This update motivates a new model for the entire Mesozoic-Eocene rifting period. Here I evaluate the link between tectonics, serpentinization and magmatism in the Norwegian margin from the Ryazanian-Valanginian to the Palaeocene-Eocene magmatic breakup. Maps of the regional Nise sandstones and main regional unconformities specifically highlight the fundamental role of the Nyk-Vema Structure to understand the basin and to question the deformation timing related to deep structures. The top of partially serpentinized mantle is supported by high-amplitude reflectors clearly visible on certain seismic lines, known as “T-Reflector”, covered with gravity-driven pre-exhumation sediments and further deposits. A new structural scheme based on the interpretation of 2D and 3D seismic data shows the complex organization of fault networks and constrains a major deformation period between the Late Campanian and the Late Palaeocene. Ocean-scale complementary arguments are in good agreement with Lower-Cretaceous mantle exhumation. Before becoming a volcanic margin in the Palaeocene, this segment of the Norwegian margin appears as amagmatic until the Late Campanian, at least. I propose an integrated model since the onset of hyperextension in the end of the Jurassic until the cessation of activity of the Aegir Ridge in the Miocene. This model has implications regarding the context-dependent interpretation of lower-crustal bodies, the ubiquity of serpentinization and mantle exhumation worldwide, and on the hydrocarbon system.

Fault interpretation in seismic reflection data: an experiment analysing the impact of conceptual model anchoring and vertical exaggeration

Abstract. The use of conceptual models is essential in the interpretation of reflection seismic data. It allows interpreters to make geological sense of seismic data, which carries inherent uncertainty. However, conceptual models can create powerful anchors that prevent interpreters from reassessing and adapting their interpretations as part of the interpretation process, which can subsequently lead to flawed or erroneous outcomes. It is therefore critical to understand how conceptual models are generated and applied to reduce unwanted effects in interpretation results. Here we have tested how interpretation of vertically exaggerated seismic data influenced the creation and adoption of the conceptual models of 161 participants in a paper-based interpretation experiment. Participants were asked to interpret a series of faults and a horizon, offset by those faults, in a seismic section. The seismic section was randomly presented to the participants with different horizontal–vertical exaggeration (1:4 or 1:2). Statistical analysis of the results indicates that early anchoring to specific conceptual models had the most impact on interpretation outcome, with the degree of vertical exaggeration having a subdued influence. Three different conceptual models were adopted by participants, constrained by initial observations of the seismic data. Interpreted fault dip angles show no evidence of other constraints (e.g. from the application of accepted fault dip models). Our results provide evidence of biases in interpretation of uncertain geological and geophysical data, including the use of heuristics to form initial conceptual models and anchoring to these models, confirming the need for increased understanding and mitigation of these biases to improve interpretation outcomes.

Predicting Missing Seismic Velocity Values Using Self-Organizing Maps to Aid the Interpretation of Seismic Reflection Data from the Kevitsa Ni-Cu-PGE Deposit in Northern Finland

We use self-organizing map (SOM) analysis to predict missing seismic velocity values from other available borehole data. The site of this study is the Kevitsa Ni-Cu-PGE deposit within the mafic-ultramafic Kevitsa intrusion in northern Finland. The site has been the target of extensive seismic reflection surveys, which have revealed a series of reflections beneath the Kevitsa resource area. The interpretation of these reflections has been complicated by disparate borehole data, particularly because of the scarce amount of available sonic borehole logs and the varying practices in logging of borehole lithologies. SOM is an unsupervised data mining method based on vector quantization. In this study, SOM is used to predict missing seismic velocities from other geophysical, geochemical, geological, and geotechnical data. For test boreholes, for which measured seismic velocity logs are also available, the correlation between actual measured and predicted velocities is strong to moderate, depending on the parameters included in the SOM analysis. Predicted reflectivity logs, based on measured densities and predicted velocities, show that some contacts between olivine pyroxenite/olivine websterite-dominant host rocks of the Kevitsa disseminated sulfide mineralization—and metaperidotite—earlier extensively used “lithology” label that essentially describes various degrees of alteration of different olivine pyroxenite variants—are reflective, and thus, alteration can potentially cause reflectivity within the Kevitsa intrusion.

3D mapping and gravity modelling of Capel and Faust basins

The Capel and Faust basins lie at water depths of 1500- 3000 m, 800 km east of Brisbane. Geoscience Australia began a petroleum prospectivity study of these remote frontier basins with acquisition of reflection and refraction seismic, gravity, magnetic and multi-beam bathymetry data during 2006/07. The approach mapped a complex distribution of sub-basins via traditional 2D reflection seismic interpretation techniques and 3D mapping and gravity modelling. Gravity models were used to inform the seismic interpretation of basement. Gravity models had three sediment layers with average densities inferred from refraction modelling of 1.85, 2.13, 2.31 t/m3 overlying a pre-rift basement of density 2.54 t/m3, itself consisting in part of intruded older basin material. Gravity modelling of the simple density model arising from the initial interpretation of reflection seismic data indicated a first order agreement between observed and calculated data. Second order misfits were accounted for by adjustments to the sediment density values, localised adjustments to basement depths, and heterogeneity in the basement densities. The study concluded that sediment of average velocity 3500 m/s exceeds 6000 m thickness in the northwest of the area, which is sufficient for potential petroleum generation.

Utilization of AEM Methods for Cost-Effective Mapping of Shallow Neogene Intra-Plate Fault Systems in Eastern Australian Coal Seam Gas Basins

Neogene fault systems are increasingly recognised as an important control on hydraulic connectivity in some of Australia’s energy rich basins. However, accurate delineation of these faults systems is challenging and expensive. In this context, the main objective of the Exploring for the Future (EFTF) Surat-Galilee Basin (Phase 1) Project is to test novel methods for more cost-effective mapping of Neogene fault systems in the Coal Seam Gas (CSG) basins of eastern Australia. Methods assessed in this project include morphotectonic mapping using temporal remote sensing data and high-resolution terrain mapping techniques, airborne electromagnetics (AEM), and the use of earthquake databases to inform active tectonic and geomechanical analysis. The project is funded by Geoscience Australia (GA) as part of its EFTF Programme, and is focussed on exemplar areas in the Surat and Galilee Basins where Neogene fault activity has been interpreted on high-resolution 2D and 3D seismic reflection surveys. This paper reports on the use of airborne electromagnetics (AEM) for detecting near-surface (<50–150m) Neogene faults in both basins. Approximately 4,500 line km of AEM data were acquired in a number of smaller acquisition blocks where Neogene faults had previously been identified. The AEM inversion results are compared with interpretation of seismic reflection data, morphotectonic mapping, and other hydrogeological and tectonic/geomechanical data. The utility of AEM to map the broader hydrogeological system in these basins, including groundwater-surface water connectivity (springs and rivers), is also assessed.

Structural implications of strain localization towards a continental transform fault: The example of the shift between the Levant margin and the Dead Sea Fault plate boundary

Continental transform faults accommodate lateral motion between two adjacent plates. Often, evidence for such motion is hard to detect due to onland processes of erosion. Investigation of a submerged passive continental margin adjacent to a transform plate boundary might provide indications for the developmental stages of the transform. To examine this hypothesis, we analyzed the Messinian-to-recent stratigraphy and structure of the Levant continental margin that resides ca. 100 km from the Dead Sea fault (DSF) continental transform. The analysis is based on interpretation of seismic reflection data (2D and 3D time migrated, and pre-stack 3D depth migrated) and four boreholes. It includes construction of structural maps, tracking of stacking patterns and calculations of sedimentation rates. Data show that the Levant margin developed through three phases: (1) Late Miocene-Earliest Zanclean (∼6-∼5 Ma) NNE-SSW left lateral strike-slip faulting (2) Zanclean-Late Gelasian (∼5–1.8 Ma) syn-depositional folding striking in the same direction. The top Gelasian surface marks an abrupt change, which is expressed as (3) mass slumping that occurred due to regional basinward tilt. Continuation of differential subsidence is manifested by Calabrian-to-recent progradation (1.8–0 Ma). While Nile sediment flux peaked at 1.8 Ma and decreased during the Calabrian-to-recent, our data shows an increase in sedimentation on the Levant margin throughout the entire Plio-Pleistocene. This discrepancy is caused by the regional tilting of phase 3, which shifted the depocenter to the west. Correlations to onshore findings suggest that the faulting, folding and tilting observed on the continental margin represent localization of strain towards the DSF during the Pliocene-Gelasian (5.3–1.8 Ma). This is attributed to the consequent deepening of the DSF and the incipient collision of the Eratosthenes Seamount with the Cyprus Arc. The continental margin records the development of the nearby active transform through structural and sedimentary modifications.

Structural validation as an input into seismic depth conversion to decrease assigned structural uncertainty

While the interpretation of seismic reflection imagery is powerful and well established for evaluating subsurface structures it is never perfectly accurate. Structural validation techniques are widely used to geometrically test geological interpretations of seismic reflection data. Commonly these techniques are performed on depth sections converted from seismic time-based data using velocity models. Velocity model choices in seismic depth conversion have an impact on the final depth image and hence the structural geometry of interpretations. The impact of these choices in depth conversion on structural validation is rarely examined. Here we explore how multiple versions of a depth section, converted using different velocity models, influence the performance of structural validations for a fold-thrust structure from the deep water Niger Delta. The example illustrates that a range of kinematic models can validate the depth-converted profiles, regardless of the depth conversion choice and are thus poor diagnostic tools. Area-depth-strain (ADS) analysis can constrain the choice both of a kinematic model and the depth conversion, provided the seismic data allow the detachment level and excess areas to be recognised. Incorporation of ADS analysis within an interpretation-depth conversion workflow helps reduce assigned uncertainty in depth conversion, the seismic interpretation, and in the implicit geological model.

Gondwana breakup: no evidence for a Davie Fracture Zone offshore northern Mozambique, Tanzania and Kenya

AbstractPlate tectonic reconstructions assume a major inactive transform fault, the Davie Fracture Zone, in the West Somali Basin, along which Madagascar is thought to have migrated southwards following Gondwana breakup in the Mesozoic. Based on the interpretation of reflection seismic data, we show that the Walu Ridge offshore Kenya and the Kerimbas Basin offshore northern Mozambique are tectonically unrelated to the southward motion of Madagascar and correlate with Late Cretaceous volcanism and inversion in Kenya and the evolution of the East African Rift System respectively. Offshore Tanzania, geophysical data do not show basement structures indicating the presence of a major transform fault. These results challenge the commonly supported transform margin concept and imply a more southerly pre‐breakup position of Madagascar within Gondwana. Opening of the West Somali Basin by SW‐propagating oblique rifting and seafloor spreading is proposed.

Wavelet‐based cepstrum decomposition of seismic data and its application in hydrocarbon detection

ABSTRACTHow to use cepstrum analysis for reservoir characterization and hydrocarbon detection is an initial question of great interest to exploration seismologists. In this paper, wavelet‐based cepstrum decomposition is proposed as a valid technology for enhancing geophysical responses in specific frequency bands, in the same way as traditional spectrum decomposition methods do. The calculation of wavelet‐based cepstrum decomposition, which decomposes the original seismic volume into a series of common quefrency volumes, employs a sliding window to move over each seismic trace sample by sample. The key factor in wavelet‐based cepstrum decomposition is the selection of the sliding‐window length as it limits the frequency ranges of the common quefrency section. Comparison of the wavelet‐based cepstrum decomposition with traditional spectrum decomposition methods, such as short‐time Fourier transform and wavelet transform, is conducted to demonstrate the effectiveness of the wavelet‐based cepstrum decomposition and the relation between these two technologies. In hydrocarbon detection, seismic amplitude anomalies are detected using wavelet‐based cepstrum decomposition by utilizing the first and second common quefrency sections. This reduces the burden of needing dozens of seismic volumes to represent the response to different mono‐frequency sections in the interpretation of spectrum decomposition in conventional spectrum decomposition methods. The model test and the application of real data acquired from the Sulige gas field in the Ordos Basin, China, confirm the effectiveness of the seismic amplitude anomaly section using wavelet‐based cepstrum decomposition for discerning the strong amplitude anomalies at a particular quefrency buried in the broadband seismic response. Wavelet‐based cepstrum decomposition provides a new method for measuring the instantaneous cepstrum properties of a reservoir and offers a new field of processing and interpretation of seismic reflection data.

Improving 2D seismic interpretation in challenging settings by integration of restoration techniques: A case study from the Jura fold-and-thrust belt (Switzerland)

The structural geologic interpretation of reflection seismic data is affected by conceptual uncertainty, particularly in challenging onshore settings. This uncertainty can be significantly reduced by the integration of cross-section restoration and balancing techniques into the seismic interpretation workflow. Moreover, these techniques define a solid and comprehensive basis, grounding the interpretation and allowing a closer investigation of the deformation history that led to the interpreted structures. These benefits are demonstrated on the basis of a case study from the eastern Jura Mountains in northern Switzerland. This mountain range was formed by a thin-skinned foreland fold-and-thrust belt with a multiphase prethrusting tectonic history. Despite significant seismic acquisition and processing efforts, seismic imaging of the strongly deformed parts of the belt widely remains ambiguous. We have developed a detailed systematic interpretation workflow that is exemplified here for a single seismic profile across the Jura Main Thrust. Classical cross-section balancing techniques of equal bed lengths and areas were applied to validate and reinterpret the given seismic interpretation. Our results suggest that most of the observed structures resulted from thin-skinned deformation along a basal décollement in Lower Triassic evaporites, which is generally inferred for the Jura Mountains. Nevertheless, secondary detachment levels in above lying strata have to be considered as well. The stepwise restoration of the analyzed cross section points toward different styles of thin-skinned deformation and possibly several episodes of earlier basement-rooted faulting events, which are indicated by subtle stratigraphic thickness changes. In summary, our workflow allowed us to significantly improve the original seismic interpretation, highlight specific deformation styles, and illuminate possible prethrusting deformation events that would otherwise be easily overlooked.

Geologic pattern recognition from seismic attributes: Principal component analysis and self-organizing maps

Interpretation of seismic reflection data routinely involves powerful multiple-central-processing-unit computers, advanced visualization techniques, and generation of numerous seismic data types and attributes. Even with these technologies at the disposal of interpreters, there are additional techniques to derive even more useful information from our data. Over the last few years, there have been efforts to distill numerous seismic attributes into volumes that are easily evaluated for their geologic significance and improved seismic interpretation. Seismic attributes are any measurable property of seismic data. Commonly used categories of seismic attributes include instantaneous, geometric, amplitude accentuating, amplitude-variation with offset, spectral decomposition, and inversion. Principal component analysis (PCA), a linear quantitative technique, has proven to be an excellent approach for use in understanding which seismic attributes or combination of seismic attributes has interpretive significance. The PCA reduces a large set of seismic attributes to indicate variations in the data, which often relate to geologic features of interest. PCA, as a tool used in an interpretation workflow, can help to determine meaningful seismic attributes. In turn, these attributes are input to self-organizing-map (SOM) training. The SOM, a form of unsupervised neural networks, has proven to take many of these seismic attributes and produce meaningful and easily interpretable results. SOM analysis reveals the natural clustering and patterns in data and has been beneficial in defining stratigraphy, seismic facies, direct hydrocarbon indicator features, and aspects of shale plays, such as fault/fracture trends and sweet spots. With modern visualization capabilities and the application of 2D color maps, SOM routinely identifies meaningful geologic patterns. Recent work using SOM and PCA has revealed geologic features that were not previously identified or easily interpreted from the seismic data. The ultimate goal in this multiattribute analysis is to enable the geoscientist to produce a more accurate interpretation and reduce exploration and development risk.

Characterization of a heterogeneous landfill using seismic and electrical resistivity data

Understanding the processes occurring inside a landfill is important for improving the treatment of landfills. Irrigation and recirculation of leachate are widely used in landfill treatments. Increasing the efficiency of such treatments requires a detailed understanding of the flow inside the landfill. The flow depends largely on the heterogeneous distribution of density. It is, therefore, of great practical interest to determine the density distribution affecting the flow paths inside a landfill. Studies in the past have characterized landfill sites but have not led to high-resolution, detailed quantitative results. We performed an S-wave reflection survey, multichannel analysis of surface waves (MASW), and electrical resistivity survey to investigate the possibility of delineating the heterogeneity distribution in the body of a landfill. We found that the high-resolution S-wave reflection method offers the desired resolution. However, in the case of a very heterogeneous landfill and a high noise level, the processing of high-resolution, shallow reflection data required special care. In comparison, MASW gave the general trend of the changes inside the landfill, whereas the electrical resistivity (ER) survey provides useful clues for interpretation of seismic reflection data. We found that it is possible to localize fine-scale heterogeneities in the landfill using the S-wave reflection method using a high-frequency vibratory source. Using empirical relations specific to landfill sites, we then estimated the density distribution inside the landfill, along with the associated uncertainty considering different methods. The final interpretation was guided by supplementary information provided by MASW and ER tomography.

New discovery and geological significance of Late Silurian–Carboniferous extensional structures in Tarim Basin

Late Silurian–Carboniferous extensional structures have been discovered after careful interpretation of seismic reflection data in western Manjiaer Sag, Central Tarim Basin in central Asia. The extensional structures comprise numerous small normal faults in nearly N–S strike direction. Groups of normal faults in profile show features suggestive of negative flower structures and small horst-graben structures. Based on growth index calculation, these extensional structures formed in the Late Silurian period, continued activity in the Devonian and Carboniferous and then ceased at the end of Carboniferous. The peak-stage of normal fault activity occurred in Late Silurian. Late Silurian–Carboniferous normal faults also developed in the Tazhong and Tabei areas, which implies that Tarim Basin were under regional extensional tectonic setting during that periods. The extensional structure in southern Tarim resulted from the post-orogeny stress relaxation of the Kunlun Early Paleozoic orogenic belt, and those in northern Tarim resulted from the Paleozoic back-arc rifting which led to the opening of South Tianshan ocean.