Evidence of tectonic reactivation after continental breakup in the Ceará Terrace, Equatorial margin of Brazil, from 2D reflection seismics

2020 ◽  
Author(s):  
Aline Cristine Tavares ◽  
David Lopes de Castro ◽  
Ole Rønø Clausen ◽  
Diógenes Custódio de Oliveira ◽  
Francisco Hilario R. Bezerra ◽  
...  
Keyword(s):  
Oil And Gas ◽  
Evolutionary Process ◽  
Spreading Center ◽  
Equatorial Atlantic ◽  
Borehole Data ◽  
Reflection Seismic ◽  
Oceanic Spreading ◽  
Reflection Seismics ◽  
Seismic Sections ◽  
Transform Margin

<p>The Brazilian equatorial margin has its origin in the fragmentation of the supercontinent Pangea with the separation of the South American and African continents and is composed of divergent oblique and transform segments related to large oceanic fracture zones, which are typical of the Equatorial Atlantic (e.g., Saint Paul, Romanche, and Chain). The dynamic evolution of this margin is related to the generation of marginal ridges, which are basement highs that follow the same trend of the continental-oceanic boundary in a transform margin.</p><p>The Ceará Terrace (CT), the main target of this investigation, is an E-W-striking marginal ridge located south of the western end of the Romanche Fracture Zone (RFZ) in the continental margin of Brazil. The CT has a counterpart in the African margin, the Ivory Coast-Ghana Ridge (ICGR), which is located north of the eastern termination of the RFZ. Earlier studies show that the evolution of both marginal ridges (CT and ICGR) was mainly influenced by (1) tectonic uplift due to Late Albian-Cenomanian transpressional tectonics and (2) flexural uplift due to erosion and thermal changes caused by the passage of the oceanic spreading center.</p><p>While ICGR is the most intensely studied marginal ridge in the Atlantic equatorial margin, the CT still needs further analysis to unravel its evolutionary process. The objective of the present study is thus to map and analyze the CT to understand its time and spatial evolution. Therefore, we have used and interpreted 2D reflection seismic sections and boreholes from the Brazilian Agency of Oil and Gas.</p><p>Our study shows that the CT is an intensely deformed Lower Cretaceous structure, which originates from the Atlantic opening process. The CT is controlled by the RZF and preexisting fault zones in the continent such as the Transbrasiliano lineament (TB). The interpretation of the seismic sections shows an intense ductile and brittle deformation of the CT paleo structure (syn-rift sequence) and the sedimentary units deposited after it (drift sequence). It indicates that tectonic reactivation occurred in the period where the transform movements were already restricted to the furthest spreading center. There is also evidence that some faults affect the whole rift sequence suggesting a possible brittle reactivation of the offshore continuation of the TB due to changes in plate movements in the Late Albian. This plate shifts agrees with previous works that show compressional features concentrated in continental shelf near of CT and half-grabens linked with the offshore TB prolongation. On the other hand, there is no evidence of the influence of weakness zones in the CIGR, where the Kandi lineament (the prolongation of the TB in the African continent) is far more than 300 km of that marginal ridge.</p><p> </p><p>Acknowledgments:</p><p>This research was supported by Programa Institucional de Internacionalização - Coordenação de Aperfeiçoamento de Pessoal (PRINT-CAPES) and Aarhus University (AU). Brazilian Agency of Oil and Natural Gas (ANP) is thanked for providing the seismic and borehole data. We also thank Schlumberger for giving access to Petrel.</p>

Automated phase attribute-based picking applied to reflection seismics

Geophysics ◽  
2016 ◽  
Vol 81 (2) ◽  
pp. V141-V150 ◽  
Author(s):  
Emanuele Forte ◽  
Matteo Dossi ◽  
Michele Pipan ◽  
Anna Del Ben
Keyword(s):  
Signal To Noise Ratio ◽  
Phase Method ◽  
Data Sets ◽  
Reflection Seismic ◽  
Instantaneous Phase ◽  
Whole Process ◽  
Specific Analysis ◽  
Reflection Seismics ◽  
Selection Of ◽  
Energy Package

We have applied an attribute-based autopicking algorithm to reflection seismics with the aim of reducing the influence of the user’s subjectivity on the picking results and making the interpretation faster with respect to manual and semiautomated techniques. Our picking procedure uses the cosine of the instantaneous phase to automatically detect and mark as a horizon any recorded event characterized by lateral phase continuity. A patching procedure, which exploits horizon parallelism, can be used to connect consecutive horizons marking the same event but separated by noise-related gaps. The picking process marks all coherent events regardless of their reflection strength; therefore, a large number of independent horizons can be constructed. To facilitate interpretation, horizons marking different phases of the same reflection can be automatically grouped together and specific horizons from each reflection can be selected using different possible methods. In the phase method, the algorithm reconstructs the reflected wavelets by averaging the cosine of the instantaneous phase along each horizon. The resulting wavelets are then locally analyzed and confronted through crosscorrelation, allowing the recognition and selection of specific reflection phases. In case the reflected wavelets cannot be recovered due to shape-altering processing or a low signal-to-noise ratio, the energy method uses the reflection strength to group together subparallel horizons within the same energy package and to select those satisfying either energy or arrival time criteria. These methods can be applied automatically to all the picked horizons or to horizons individually selected by the interpreter for specific analysis. We show examples of application to 2D reflection seismic data sets in complex geologic and stratigraphic conditions, critically reviewing the performance of the whole process.

scholarly journals Role of multiple reflections in the formationof wave field in the cretaceous successions of the Middli Kura depression in Azerbaijan

2021 ◽  
Vol 43 (3) ◽  
pp. 123-134
Author(s):  
T. R. Akhmedov ◽  
T. Kh. Niyazov
Keyword(s):  
Wave Field ◽  
Upper Cretaceous ◽  
Oil And Gas ◽  
Geophysical Methods ◽  
Geological Structure ◽  
Gas Content ◽  
Seismic Exploration ◽  
Time Interval ◽  
Multiple Reflections ◽  
Seismic Sections

The article is devoted to the elucidation of the nature of the wave field recorded below the supporting-dominant seismic horizon «P» in the Middle Kura depression of Azerbaijan. A brief overview of the work carried out here is given; it is indicated that some geologists and geophysicists of our country, in our opinion, mistakenly assume that the observed wave field below the specified horizon is formed mainly by multiple reflections. Since the introduction of the common depth point method into the practice of seismic exploration, individual areas of the Middle Kura depression in Azerbaijan, including the Yevlakh-Agjabedi trough, have been repeatedly studied with varying degrees of frequency tracking. On the basis of this, a fairly large number of promising structures have been identified and mapped. But the structure of the Mesozoic, in particular the deposits of the Upper Cretaceous, still remains insufficiently studied. The study of the geological structure of the Mesozoic sediments, which are considered promising in terms of oil and gas content, is an urgent geological task; exploration work was carried out in the studied areas of the Middle Kura depression using a complex of geophysical methods at the modern technical and methodological level and new results were obtained. The constructed seismic sections show a dynamically pronounced and well-traceable seismic horizon corresponding to the Mesozoic surface and located deeper than it, relatively weak, short, discontinuous reflective boundaries that characterize the structure within the Mesozoic deposits. The studies carried out on the basis of modeling and velocity analysis made it possible to prove that the wave field in the time interval corresponding to the Mesozoic deposits owes its origin to intermittent single reflections from volcanic-carbonate deposits of the Upper Cretaceous age.

scholarly journals Structural analysis of S-wave seismics around an urban sinkhole; evidence of enhanced subrosion in a strike-slip fault zone

2017 ◽  
Author(s):  
Sonja H. Wadas ◽  
David C. Tanner ◽  
Ulrich Polom ◽  
Charlotte M. Krawczyk
Keyword(s):  
Strike Slip ◽  
Strike Slip Fault ◽  
Key Factors ◽  
S Wave ◽  
Seismic Profiles ◽  
Reflection Seismic ◽  
Dextral Strike Slip Fault ◽  
Seismic Sections ◽  
The Town ◽  
Dextral Strike Slip

Abstract. In November 2010, a large sinkhole opened up in the urban area of Schmalkalden, Germany. To determine the key factors which benefited the development of this collapse structure and therefore the subrosion, we carried out several shear wave reflection seismic profiles around the sinkhole. In the seismic sections we see evidence of the Mesozoic tectonic movement, in the form of a NW–SE striking, dextral strike-slip fault, known as the Heßleser Fault, which faulted and fractured the subsurface below the town. The strike-slip faulting created a zone of small blocks (

Groundwater exploration using combined controlled-source and radiomagnetotelluric techniques

Geophysics ◽  
2005 ◽  
Vol 70 (1) ◽  
pp. G8-G15 ◽  
Author(s):  
Laust B. Pedersen ◽  
M. Bastani ◽  
L. Dynesius
Keyword(s):  
Transfer Functions ◽  
Three Dimensional ◽  
Groundwater Exploration ◽  
Impedance Tensor ◽  
Two Dimensional ◽  
Controlled Source ◽  
Reflection Seismic ◽  
Seismic Sections ◽  
Clay Layers ◽  
Clay Lenses

Radiomagnetotelluric (RMT) (14–250 kHz) combined with controlled-source magnetotelluric (CSMT) (1–12 kHz) measurements were applied to the exploration of groundwater located in sandy formations at depths as great as 20 m below thick clay lenses. A combination of approximately 30 radio frequencies and controlled-source frequencies is essential for penetrating the thick clay layers. The electromagnetic transfer functions of impedance tensor and tipper vectors point toward a structure that is largely two-dimensional, although clear three-dimensional effects can be observed where the sandy formation is close to the surface. The determinant of the impedance tensor was chosen for inversion using two-dimensional models. The final two-dimensional model fits the data to within twice the estimated standard errors, which is considered quite satisfactory, given that typical errors are on the level of 1% on the impedance elements. Comparison with bore-hole results and shallow-reflection seismic sections show that the information delivered by the electromagnetic data largely agrees with the former and provides useful information for interpreting the latter by identifying lithological boundaries between the clay and sand and between the sand and crystalline basement.

Integrated interpretation of reflection seismic and aeromagnetic data in a marine geological complex area: a case study.

2020 ◽  
Author(s):  
Silvana Fais ◽  
Emile Eduard Klingele ◽  
Raffaele Tocco ◽  
Giuseppe Casula
Keyword(s):  
Magnetic Anomaly ◽  
Tectonic Evolution ◽  
Analytical Signal ◽  
Western Mediterranean ◽  
Aeromagnetic Data ◽  
Reflection Seismic ◽  
Magnetic Pattern ◽  
Volcanic Source ◽  
Integrated Interpretation ◽  
Seismic Sections

<p>This paper presents an integrated seismic and aeromagnetic approach applied in the geological complex area of the Cagliari Gulf in the southern Sardinian margin (Western Mediterranean). The investigated area represents the southern extreme part of the main branch of the Sardinian Rift (SR) (Western Mediterranean) that is made up here of a sub-basin bounded by approximately NW faults. The study was also integrated by complementary information deduced from the GNSS network in southern Sardinia.</p><p>The aim of this study was to give a contribution on the knowledge of the tectonic evolution and volcanism of the investigated area. For this purpose we used an integrated interpretation of two-dimensional reflection seismic sections and aeromagnetic data. In the same area a well drilled for oil prospection was used for calibrating the seismic interpretation up to approximately 1.8 sec.. It is worth noting that the interpretation of the seismic data can be problematic in structurally complex areas where volcanic formations occur, but it can be assisted effectively by magnetic interpretation. An interesting magnetic pattern represented by a strong, well-localized positive magnetic anomaly extending N-S for approximately 35 km is present in the western part of the Gulf. Its width in the W-E direction is of almost 20 km. The anomaly seems to be linked with the magnetic anomalies that characterize the southern Sardinian Rift in correspondence to the Campidano Graben. In fact, a set of localized high-gradient anomalies generally corresponding to the Oligo-Miocene andesitic calc-alkaline complexes is present in this Graben. The aeromagnetic interpretation was carried out to explain the origin of the above strong elongated magnetic anomaly that has never been quantitatively interpreted. In this work, this anomaly has been interpreted by means of Euler deconvolution, the analytical signal and by a delineation technique based on the maxima of the radial horizontal derivative of the total magnetic field. The geological knowledge of the area by means of earlier studies also on land contributed to give a petrographic meaning to the magnetic sources, while by the magnetic and seismic integrated interpretation it was possible to carry out a spatial reconstruction of the volcanic source body and to give an useful contribution to the knowledge on the volcano-tectonic evolution of the area. Recently the area of the Gulf of Cagliari was affected in its western sector by a weak earthquake with hypocenter at around 10 km of depth, localized by Istituto Nazionale di Geofisica e Vulcanologia (INGV). The results of this study also provided new elements of knowledge which have contributed to understand this seismic event.</p><p>Acknowledgements: This work was partially supported by FIR (Fondi integrativi per la Ricerca) funded by the University of Cagliari (Italy) and by RAS/FBS (grant number: F71/17000190002) grants for funding.</p>

New Forms of Work and Employment in an `Old Industrial Region'? The Offshore Construction Industry in the North East of England

1994 ◽  
Vol 8 (4) ◽  
pp. 531-552 ◽  
Author(s):  
Andy Cumbers
Keyword(s):  
Labour Market ◽  
Construction Industry ◽  
Oil And Gas ◽  
Evolutionary Process ◽  
The Past ◽  
North East ◽  
The North ◽  
Local Labour ◽  
New Forms Of Work ◽  
Work And Employment

This paper examines the nature of the new forms of work and employment brought to the North East of England by the development of offshore construction activities, serving the North Sea's oil and gas industries in the period since the early 1970s. In particular, it assesses the extent to which these activities differ from traditional forms of work and employment organisation within the region. The results of this analysis suggest the need to interpret contemporary patterns of restructuring, both in a particular local labour market context and more generally, as part of an on-going evolutionary process, rather than as a decisive break (or shift) from the past.

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