Two-dimensional velocity model of the crust beneath the South Cambay Basin, India from refraction and wide-angle reflection data

Abstract. The difficulties of seismic imaging beneath high velocity structures are widely recognised. In this setting, theoretical analysis of synthetic wide-angle seismic reflection data indicates that velocity models are not well constrained. A two-dimensional velocity model was built to simulate a simplified structural geometry given by a basaltic wedge placed within a sedimentary sequence. This model reproduces the geological setting in areas of special interest for the oil industry as the Faroe-Shetland Basin. A wide-angle synthetic dataset was calculated on this model using an elastic finite difference scheme. This dataset provided travel times for tomographic inversions. Results show that the original model can not be completely resolved without considering additional information. The resolution of nonlinear inversions lacks a functional mathematical relationship, therefore, statistical approaches are required. Stochastic tests based on Metropolis techniques support the need of additional information to properly resolve sub-basalt structures.

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Lithospheric structure in northwestern Canada from Lithoprobe seismic refraction and related studies: a synthesis

Canadian Journal of Earth Sciences ◽

10.1139/e04-069 ◽

2005 ◽

Vol 42 (6) ◽

pp. 1277-1293 ◽

Cited By ~ 41

Author(s):

Ron M Clowes ◽

Philip TC Hammer ◽

Gabriela Fernández-Viejo ◽

J Kim Welford

Keyword(s):

Seismic Data ◽

Seismic Refraction ◽

Velocity Model ◽

Wide Angle ◽

Slave Craton ◽

Reflection Data ◽

Western Cordillera ◽

Thermal Constraints ◽

Geological Information ◽

Tectonic Boundaries

The SNORCLE refraction wide-angle reflection (R/WAR) experiment, SNORE'97, included four individual lines along the three transect corridors. A combination of SNORE'97 results with those from earlier studies permits generation of a 2000 km long lithospheric velocity model that extends from the Archean Slave craton to the present Pacific basin. Using this model and coincident near-vertical incidence (NVI) reflection data and geological information, an interpreted cross section that exemplifies 4 Ga of lithospheric development is generated. The velocity structural models correlate well with the reflection sections and provide additional structural, compositional, and thermal constraints. Geological structures and some faults are defined in the upper crust. At a larger scale, the seismic data identify a variety of orogenic styles ranging from thin- to thick-skinned accretion in the Cordillera and crustal-scale tectonic wedging associated with both Paleoproterozoic and Mesozoic collisions. Models of Poisson's ratio support the NVI interpretation that a thick wedge of cratonic metasediments underlies the eastern accreted Cordilleran terranes. Despite the variety of ages, orogenic styles, and tectono-magmatic deformations that are spanned by the seismic corridors, the Moho remains remarkably flat and shallow (3336 km) across the majority of the transect. Significant variations only occur at major tectonic boundaries. Laterally variable crustal velocities are consistently slower beneath the Cordillera than beneath the cratonic crust. This is consistent with the high temperatures (800900 °C) required by the slow upper mantle velocities (7.87.9 km/s) observed beneath much of the Cordillera. Heterogeneity of the lithospheric mantle is indicated by wide-angle reflections below the Precambrian domains and the western Cordillera.

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Two-dimensional Crustal Velocity Structure along Hirapur-Mandla Profile from Seismic Refraction and Wide-angle Reflection Data

Pure and Applied Geophysics ◽

10.1007/s000240050153 ◽

1998 ◽

Vol 152 (2) ◽

pp. 247-266 ◽

Cited By ~ 16

Author(s):

A. S. N. Murty ◽

D. M. Mall ◽

P. R. K. Murty ◽

P. R. Reddy

Keyword(s):

Velocity Structure ◽

Seismic Refraction ◽

Wide Angle ◽

Two Dimensional ◽

Reflection Data ◽

Crustal Velocity ◽

Crustal Velocity Structure

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Study on the limitations of traveltime inversion in the presence of extreme velocity anomalies

Solid Earth Discussions ◽

10.5194/sed-5-189-2013 ◽

2013 ◽

Vol 5 (1) ◽

pp. 189-226

Author(s):

I. Flecha ◽

R. Carbonell ◽

R. W. Hobbs

Keyword(s):

Oil Industry ◽

Velocity Model ◽

Wide Angle ◽

Seismic Reflection Data ◽

Traveltime Inversion ◽

Additional Information ◽

Velocity Models ◽

Reflection Data ◽

Velocity Anomalies ◽

Tomographic Inversions

Abstract. The difficulties of seismic imaging beneath high velocity structures are widely recognised. In this setting, theoretical analysis of synthetic wide-angle seismic reflection data indicates that velocity models are not well constrained. A two-dimensional velocity model was built to simulate a simplified structural geometry given by a basaltic wedge placed within a sedimentary sequence. This model reproduces the geological setting in areas of special interest for the oil industry as the Faroe-Shetland Basin. A wide-angle synthetic dataset was calculated on this model using an elastic finite difference scheme. This dataset provided travel times for tomographic inversions. Results show that the original model can not be completely resolved without considering additional information. The resolution of nonlinear inversions lacks a functional mathematical relationship, therefore, statistical approaches are required. Stochastical tests based on Metropolis techniques support the need of additional information to properly resolve subbasalt structures.

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c-Perpendicular Orientation of Poly(ʟ-lactide) Films

Polymers ◽

10.3390/polym13101572 ◽

2021 ◽

Vol 13 (10) ◽

pp. 1572

Author(s):

Baku Nagendra ◽

Paola Rizzo ◽

Christophe Daniel ◽

Lucia Baldino ◽

Gaetano Guerra

Keyword(s):

Low Temperature ◽

Film Plane ◽

Wide Angle ◽

Two Dimensional ◽

X Ray Diffraction ◽

Amorphous Films ◽

High Transparency ◽

X Ray ◽

Crystalline Forms ◽

Induced Crystallization

Poly(ʟ-lactide) (PLLA) films, even of high thickness, exhibiting co-crystalline and crystalline α phases with their chain axes preferentially perpendicular to the film plane (c⊥ orientation) have been obtained. This c⊥ orientation, unprecedented for PLLA films, can be achieved by the crystallization of amorphous films as induced by low-temperature sorption of molecules being suitable as guests of PLLA co-crystalline forms, such as N,N-dimethylformamide, cyclopentanone or 1,3-dioxolane. This kind of orientation is shown and quantified by two-dimensional wide-angle X-ray diffraction (2D-WAXD) patterns, as taken with the X-ray beam parallel to the film plane (EDGE patterns), which present all the hk0 arcs centered on the meridian. PLLA α-form films, as obtained by low-temperature guest-induced crystallization, also exhibit high transparency, being not far from those of the starting amorphous films.

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Data-driven wavefield focusing and imaging with multidimensional deconvolution: Numerical examples for reflection data with internal multiples

Geophysics ◽

10.1190/geo2013-0307.1 ◽

2014 ◽

Vol 79 (3) ◽

pp. WA107-WA115 ◽

Cited By ~ 67

Author(s):

Filippo Broggini ◽

Roel Snieder ◽

Kees Wapenaar

Keyword(s):

Green’S Function ◽

Green's Function ◽

Imaging Techniques ◽

Velocity Model ◽

Single Scattering ◽

Data Driven ◽

Multiple Reflections ◽

Prestack Migration ◽

Reflection Data ◽

Internal Multiples

Standard imaging techniques rely on the single scattering assumption. This requires that the recorded data do not include internal multiples, i.e., waves that have bounced multiple times between reflectors before reaching the receivers at the acquisition surface. When multiple reflections are present in the data, standard imaging algorithms incorrectly image them as ghost reflectors. These artifacts can mislead interpreters in locating potential hydrocarbon reservoirs. Recently, we introduced a new approach for retrieving the Green’s function recorded at the acquisition surface due to a virtual source located at depth. We refer to this approach as data-driven wavefield focusing. Additionally, after applying source-receiver reciprocity, this approach allowed us to decompose the Green’s function at a virtual receiver at depth in its downgoing and upgoing components. These wavefields were then used to create a ghost-free image of the medium with either crosscorrelation or multidimensional deconvolution, presenting an advantage over standard prestack migration. We tested the robustness of our approach when an erroneous background velocity model is used to estimate the first-arriving waves, which are a required input for the data-driven wavefield focusing process. We tested the new method with a numerical example based on a modification of the Amoco model.

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Marchenko multiple elimination and full wavefield migration in a resonant pinch-out model

Geophysics ◽

10.1190/geo2020-0867.1 ◽

2021 ◽

pp. 1-59

Author(s):

Evert Slob ◽

Lele Zhang ◽

Eric Verschuur

Keyword(s):

Constant Velocity ◽

Local Minimum ◽

Velocity Model ◽

Dominant Frequency ◽

Data Sampling ◽

Multiple Reflections ◽

Linear Inversion ◽

Acoustic Reflection ◽

Reflection Data ◽

Multiple Elimination

Marchenko multiple elimination schemes are able to attenuate all internal multiple reflections in acoustic reflection data. These can be implemented with and without compensation for two-way transmission effects in the resulting primary reflection dataset. The methods are fully automated and run without human intervention, but require the data to be properly sampled and pre-processed. Even when several primary reflections are invisible in the data because they are masked by overlapping primaries, such as in the resonant wedge model, all missing primary reflections are restored and recovered with the proper amplitudes. Investigating the amplitudes in the primary reflections after multiple elimination with and without compensation for transmission effects shows that transmission effects are properly accounted for in a constant velocity model. When the layer thickness is one quarter of the wavelength at the dominant frequency of the source wavelet, the methods cease to work properly. Full wavefield migration relies on a velocity model and runs a non-linear inversion to obtain a reflectivity model which results in the migration image. The primary reflections that are masked by interference with multiples in the resonant wedge model, are not recovered. In this case, minimizing the data misfit function leads to the incorrect reflector model even though the data fit is optimal. This method has much lower demands on data sampling than the multiple elimination schemes, but is prone to get stuck in a local minimum even when the correct velocity model is available. A hybrid method that exploits the strengths of each of these methods could be worth investigating.

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