Integrating high‐resolution refraction data into near‐surface seismic reflection data processing and interpretation

Geophysics ◽  
1998 ◽  
Vol 63 (4) ◽  
pp. 1339-1347 ◽  
Author(s):  
Kate C. Miller ◽  
Steven H. Harder ◽  
Donald C. Adams ◽  
Terry O’Donnell
Keyword(s):  
Seismic Reflection ◽  
Velocity Model ◽  
Surface Velocity ◽  
Seismic Profiles ◽  
Seismic Reflection Data ◽  
Near Surface ◽  
Interval Velocity ◽  
Velocity Models ◽  
Reflection Data ◽  
Seismic Reflection Profiles

Shallow seismic reflection surveys commonly suffer from poor data quality in the upper 100 to 150 ms of the stacked seismic record because of shot‐associated noise, surface waves, and direct arrivals that obscure the reflected energy. Nevertheless, insight into lateral changes in shallow structure and stratigraphy can still be obtained from these data by using first‐arrival picks in a refraction analysis to derive a near‐surface velocity model. We have used turning‐ray tomography to model near‐surface velocities from seismic reflection profiles recorded in the Hueco Bolson of West Texas and southern New Mexico. The results of this analysis are interval‐velocity models for the upper 150 to 300 m of the seismic profiles which delineate geologic features that were not interpretable from the stacked records alone. In addition, the interval‐velocity models lead to improved time‐to‐depth conversion; when converted to stacking velocities, they may provide a better estimate of stacking velocities at early traveltimes than other methods.

scholarly journals Stratigraphic and structural framework of the Neoproterozoic Paracuellos Group, Iberian Chains, NE Spain

2002 ◽  
Vol 173 (3) ◽  
pp. 219-227 ◽  
Author(s):  
J. Javier Álvaro ◽  
Marie-Madeleine Blanc-Valleron
Keyword(s):  
Seismic Reflection ◽  
Structural Complexity ◽  
Gradual Transition ◽  
Seismic Profiles ◽  
Seismic Reflection Data ◽  
Reflection Data ◽  
Sedimentary Evolution ◽  
Structural Framework ◽  
Bedded Chert ◽  
Seismic Reflection Profiles

Abstract The Neoproterozoic Paracuellos Group of the Iberian Chains constitutes the core of two disconnected faulted blocks, named the Paracuellos and Codos antiforms. Precise lithostratigraphic correlations between both areas are not possible due to the structural complexity and because marker beds do not persist laterally. This paper presents a crustal cross-section of the Neoproterozoic axial core (the Paracuellos antiform) based on surface geology, boreholes and seismic reflection profiles. Seismic reflection data reveal that the basement was directly involved by a major Hercynian structure, named here the Paracuellos fault, which splits longitudinally the Paracuellos axial core. In seismic profiles this fault occurs as a northeasterly-dipping reflector (60–70° steep), evidencing a bivergent geometry of the lateral crustal elements. The sedimentary evolution of the Neoproterozoic Iberian platform ranges from transgressive, non-cyclic, offshore to hemipelagic, black and green shales (Sestrica Formation) to progradational trends recording shoaling during episodes of rapid sediment influx (Saviñán Formation), presumably in response to a low standing sea-level. The siliciclastic succession is punctuated in the inner platform by deposition of phosphatic limestones (Codos Bed), representing a major shoaling event and demarcating a sharp regional change of sedimentation separating two similar siliciclastic tendencies. A diagenetically induced bedded chert (Frasno Bed) occurs in the outer platform, and is interpreted as being the product of at least two silicification episodes. Both the Codos and Frasno Beds are overlain by the Aluenda Formation, which exhibits nearshore to offshore features. An important sedimentary discontinuity appears across the Neoproterozoic-Cambrian transition. The Cambrian(?) Bámbola Formation is paraconformable with the Paracuellos Group displaying a gradual transition in inner platform areas, whereas an erosive unconformity occurs in outer areas. The horizon of the Neoproterozoic-Cambrian boundary is not identified in the Iberian Chains, where neither Cadomian deformation nor discordances are recognisable.

Large near‐surface velocity gradients on shallow seismic reflection data

Geophysics ◽  
1998 ◽  
Vol 63 (4) ◽  
pp. 1348-1356 ◽  
Author(s):  
Richard D. Miller ◽  
Jianghai Xia
Keyword(s):  
Seismic Reflection ◽  
Surface Velocity ◽  
Coherent Noise ◽  
Lower Velocity ◽  
Seismic Reflection Data ◽  
Near Surface ◽  
Reflection Data ◽  
Shallow Seismic ◽  
Velocity Gradients ◽  
Large Velocity

Extreme velocity gradients occasionally present within near‐surface materials can inhibit optimal common midpoint (CMP) stacking of near‐surface reflection arrivals. For example, abrupt increases in velocity are observed routinely at the bedrock surface and at the boundary between the vadose and the saturated zone. When a rapid increase in near‐surface velocity is found, NMO correction artifacts manifested on CMP gathers as sample reversion, sample compression, or duplication of reflection wavelets can reduce S/N ratio on stacked data or can stack coherently. Elimination of these nonstretch‐related artifacts using conventional NMO-stretch muting requires near‐vertically incident reflection arrivals and allowable stretch ratios as small as 5% in some shallow environments. Radical allowable stretch mutes are not a feasible means to subdue these artifacts if high‐amplitude coherent noise on near‐offset traces inhibits identification and digital enhancement of shallow reflections. On most shallow seismic reflection data, long‐offset reflection arrivals (but less than wide angle) are critical to the generation of an interpretable stacked section. The difference in offset between the optimum window for shallow reflections within unsaturated sediments and reflections from the underlying saturated or consolidated‐material portion of the section inherently limits the effectiveness of conventional NMO corrections. Near‐surface average velocity increases of 200% in less than two wavelengths and at two‐way traveltimes less than 60 ms are not uncommon on shallow reflection data. Near‐surface reflections separated by large velocity gradients can rarely be accurately or optimally CMP processed using conventional approaches to NMO corrections. Large velocity‐gradient shallow reflection data require segregation of shallow lower velocity reflections from higher velocity reflections during processing to maximize the accuracy and resolution potential of the stacked section, as shown by examples herein.

scholarly journals Study on the limitations of travel-time inversion applied to sub-basalt imaging

Solid Earth ◽  
2013 ◽  
Vol 4 (2) ◽  
pp. 543-554 ◽  
Author(s):  
I. Flecha ◽  
R. Carbonell ◽  
R. W. Hobbs
Keyword(s):  
Oil Industry ◽  
Velocity Model ◽  
Time Inversion ◽  
Wide Angle ◽  
Seismic Reflection Data ◽  
Additional Information ◽  
Velocity Models ◽  
Reflection Data ◽  
Travel Time Inversion ◽  
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. Stochastic tests based on Metropolis techniques support the need of additional information to properly resolve sub-basalt structures.

A multioffset, three‐component VSP study in the Sudbury Basin

Geophysics ◽  
1995 ◽  
Vol 60 (2) ◽  
pp. 341-353 ◽  
Author(s):  
Xiao‐Gui Miao ◽  
Wooil M. Moon ◽  
B. Milkereit
Keyword(s):  
Data Processing ◽  
Seismic Reflection ◽  
Velocity Structure ◽  
Least Square ◽  
Seismic Reflection Data ◽  
S Waves ◽  
Velocity Models ◽  
Reflection Data ◽  
Wavefield Separation ◽  
Vsp Data

A multioffset, three‐component vertical seismic profiling (VSP) experiment was carried out in the Sudbury Basin, Ontario, as a part of the LITHOPROBE Sudbury Transect. The main objectives were determination of the shallow velocity structure in the middle of the Sudbury Basin, development of an effective VSP data processing flow, correlation of the VSP survey results with the surface seismic reflection data, and demonstration of the usefulness of the VSP method in a crystalline rock environment. The VSP data processing steps included rotation of the horizontal component data, traveltime inversion for velocity analysis, Radon transform for wavefield separation, and preliminary analysis of shear‐wave data. After wavefield separation, the flattened upgoing wavefields for both P‐waves and S‐waves display consistent reflection events from three depth levels. The VSP-CDP transformed section and corridor stacked section correlate well with the high‐resolution surface reflection data. In addition to obtaining realistic velocity models for both P‐ and S‐waves through least‐square inversion and synthetic seismic modeling for the Chelmsford area, the VSP experiment provided an independent estimation for the reflector dip using three component hodogram analysis, which indicates that the dip of the contact between the Chelmsford and Onwatin formations, at an approximate depth of 380 m in the Chelmsford borehole, is approximately 10.5° southeast. This study demonstrates that multioffset, three‐component VSP experiments can provide important constraints and auxiliary information for shallow crustal seismic studies in crystalline terrain. Thus, the VSP technique bridges the gap between the surface seismic‐reflection technique and well‐log surveys.

Automating the acquisition of 3D near‐surface seismic reflection data

2009 ◽  
Author(s):  
Steven D. Sloan ◽  
Don W. Steeples ◽  
Georgios P. Tsoflias ◽  
Mihan H. McKenna
Keyword(s):  
Seismic Reflection ◽  
Seismic Reflection Data ◽  
Near Surface ◽  
Reflection Data

Crustal structure and surface zonation of the Canadian Appalachians: implications of deep seismic reflection data

1989 ◽  
Vol 26 (2) ◽  
pp. 305-321 ◽  
Author(s):  
François Marillier ◽  
Charlotte E. Keen ◽  
Glen S. Stockmal ◽  
Garry Quinlan ◽  
Harold Williams ◽  
...  
Keyword(s):  
Seismic Reflection ◽  
Three Dimensional ◽  
Surface Expression ◽  
Seismic Profiles ◽  
Crust And Upper Mantle ◽  
Seismic Reflection Data ◽  
Central Block ◽  
Reflection Data ◽  
Lower Crustal ◽  
Canadian Appalachians

In 1986, 1181 km of marine seismic reflection data was collected to 18–20 s of two-way traveltime in the Gulf of St. Lawrence area. The seismic profiles sample all major surface tectono-stratigraphic zones of the Canadian Appalachians. They complement the 1984 deep reflection survey northeast of Newfoundland. Together, the seismic profiles reveal the regional three-dimensional geometry of the orogen.Three lower crustal blocks are distinguished on the seismic data. They are referred to as the Grenville, Central, and Avalon blocks, from west to east. The Grenville block is wedge shaped in section, and its subsurface edge follows the form of the Appalachian structural front. The Grenville block abuts the Central block at mid-crustal to mantle depths. The Avalon block meets the Central block at a steep junction that penetrates the entire crust.Consistent differences in the seismic character of the Moho help identify boundaries of the deep crustal blocks. The Moho signature varies from uniform over extended distances to irregular with abrupt depth changes. In places the Moho is offset by steep reflections that cut the lower crust and upper mantle. In other places, the change in Moho elevation is gradual, with lower crustal reflections following its form. In all three blocks the crust is generally highly reflective, with no distinction between a transparent upper crust and reflective lower crust.In general, Carboniferous and Mesozoic basins crossed by the seismic profiles overlie thinner crust. However, a deep Moho is found at some places beneath the Carboniferous Magdalen Basin.The Grenville block belongs to the Grenville Craton; the Humber Zone is thrust over its dipping southwestern edge. The Dunnage Zone is allochthonous above the opposing Grenville and Central blocks. The Gander Zone may be the surface expression of the Central block or may be allochthonous itself. There is a spatial analogy between the Avalon block and the Avalon Zone. Our profile across the Meguma Zone is too short to seismically distinguish this zone from the Avalon Zone.

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