scholarly journals Observations of tunnel channels in glacial sediments with shallow land-based seismic reflection

1996 ◽  
Vol 22 ◽  
pp. 176-180 ◽  
Author(s):  
A. Pugin ◽  
S. E. Pullan ◽  
D. R. Sharpe
Keyword(s):  
Seismic Reflection ◽  
Three Dimensional ◽  
Seismic Profiles ◽  
Glacial Sediments ◽  
Oak Ridges Moraine ◽  
Depositional Processes ◽  
Hydrogeological Study ◽  
Seismic Sections ◽  
Seismic Reflection Profiles ◽  
Subglacial Meltwater

A regional hydrogeological study conducted by the Geological Survey of Canada acquired 35 line-km of 12-fold seismic reflection profiles on or adjacent to the Oak Ridges moraine, north of Toronto, Ontario, Canada. The three-dimensional geometry provided by these data aids in understanding the erosional and depositional processes that occurred beneath the Laurentide ice sheet during the late stages of glaciation. The seismic sections indicate large infilled channels in the subsurface which are interpreted as tunnel channels eroded by large, subglacial meltwater discharges. Two seismic profiles from different areas of the moraine show channel-cutting events of different ages and different types of infilling.

scholarly journals Observations of tunnel channels in glacial sediments with shallow land-based seismic reflection

1996 ◽  
Vol 22 ◽  
pp. 176-180 ◽  
Author(s):  
A. Pugin ◽  
S. E. Pullan ◽  
D. R. Sharpe
Keyword(s):  
Seismic Reflection ◽  
Three Dimensional ◽  
Seismic Profiles ◽  
Glacial Sediments ◽  
Oak Ridges Moraine ◽  
Depositional Processes ◽  
Hydrogeological Study ◽  
Seismic Sections ◽  
Seismic Reflection Profiles ◽  
Subglacial Meltwater

A regional hydrogeological study conducted by the Geological Survey of Canada acquired 35 line-km of 12-fold seismic reflection profiles on or adjacent to the Oak Ridges moraine, north of Toronto, Ontario, Canada. The three-dimensional geometry provided by these data aids in understanding the erosional and depositional processes that occurred beneath the Laurentide ice sheet during the late stages of glaciation. The seismic sections indicate large infilled channels in the subsurface which are interpreted as tunnel channels eroded by large, subglacial meltwater discharges. Two seismic profiles from different areas of the moraine show channel-cutting events of different ages and different types of infilling.

Seismic facies and regional architecture of the Oak Ridges Moraine area, southern Ontario

1999 ◽  
Vol 36 (3) ◽  
pp. 409-432 ◽  
Author(s):  
A Pugin ◽  
S E Pullan ◽  
D R Sharpe
Keyword(s):  
Seismic Reflection ◽  
High Energy ◽  
Seismic Facies ◽  
Coarse Grained ◽  
Oak Ridges Moraine ◽  
Shallow Seismic ◽  
Glaciofluvial Deposits ◽  
Buried Channels ◽  
Seismic Reflection Profiles ◽  
Subglacial Meltwater

Analysis of over 50 line-kilometres of land-based, shallow, seismic reflection profiles has provided a means of investigating the subsurface architecture and stratigraphic relationships of the glacial deposits in and beneath the Oak Ridges Moraine (ORM). The focus of this paper is the role of seismic reflection surveys, and the derived seismic facies and facies geometry, in the development of a well-constrained, regional, conceptual model of the subsurface stratigraphy in the area and the improved inferences these data allow regarding glacial event sequence and process interpretations. The data define four major seismic facies that characterize the complex glacial sequence of the ORM area. High-reflectivity facies (I) can be traced regionally and related to an eroded Newmarket Till surface. Medium (II) and low (III) reflectivity facies are generally associated with coarse-grained glaciofluvial deposits and laterally extensive, glaciolacustrine sequences of sand, silt, and clay, respectively. A chaotic facies (IV) is common within buried channels, and attributed to instability and (or) rapid channel-fill deposition. Seismic geometry (with borehole verification) shows that a broad surface network of channels extends below thick ORM sediments. The channel system is part of a regional unconformity formed on the Newmarket Till (facies I). The buried channels can have steep sides, and their fills frequently include tabular sheets, eskers, and (or) large cross-beds. The observations are consistent with the scenario of sheet flow and channel cutting by high-energy subglacial meltwater and filling with gravel, sand, and silt in succession (facies II and III) as the flows waned.

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.

scholarly journals STUDY OF THE ARCHITECTURE OF SEDIMENTARY DEPOSITS IN THE IVORIAN ONSHORE BASIN THROUGH SEISMIC REFLECTION

2020 ◽  
Vol 8 (12) ◽  
pp. 575-584
Author(s):  
Assa Maxime Abbey ◽  
◽  
Loukou Nicolas Kouame ◽  
Lacine Coulibaly ◽  
Simon Pierre Djroh ◽  
...  
Keyword(s):  
Seismic Reflection ◽  
Upper Cretaceous ◽  
Seismic Facies ◽  
Seismic Profiles ◽  
Sedimentary Deposits ◽  
Sedimentary Model ◽  
Seismic Sections ◽  
Two Phases ◽  
Two Stages ◽  
Stratigraphic Evolution

The seismic profiles analysis of 4,533 km study area made it possible to study the sedimentary deposits in the Ivorian onshore basin. The method used consisted of manual plots of the seismic sections leading to the production of isochronos, iso-velocity, isobaths and isopac maps. As for the stratigraphic interpretation, it was used to develop a sedimentary model to extract information on the nature of sedimentary deposits and the mechanisms of their establishment based on the analysis of seismic facies. Examination of the different seismic profiles of the study area allowed the onshore sedimentary series to be subdivided into four main sequences which are: sequences I, II, III and IV. Thus, this analysis revealed two stages of sedimentary deposits linked to the behavior of the reflectors: 1. a syn-rift stage, characterized by significant fracturing in the sedimentation with faults and tilted blocks inthe Lower Cretaceous 2. a post-rift stage , corresponding to a less deformed sedimentation with parallel and continuous reflectors from the Upper Cretaceous to the present . These two phases allow us to understand the stratigraphic evolution of the onshore basin.

scholarly journals Interpretation of shallow seismic profiles over the continental shelf in West Greenland between latitudes 64° and 69°30'N

1980 ◽  
Vol 100 ◽  
pp. 58-61
Author(s):  
E.F.K Zarudzki
Keyword(s):  
Continental Shelf ◽  
Seismic Reflection ◽  
Preliminary Report ◽  
Early Stage ◽  
Sidescan Sonar ◽  
Seismic Profiles ◽  
West Greenland ◽  
Shallow Seismic ◽  
Seismic Reflection Profiles

The work included the study of parts of the data obtained during the survey cruise WESTMAR 78, described in a preliminary report (Brett & Zarudzki, 1979). The data consist of 10 741 km seismic reflection profiles obtained with sparker, sub-bottom, airgun and boomer systems; 8474 km of bathymetric profiles, 3894 km of sidescan sonar profiles and 8545 km of magnetic profiles. The study objectives in the area and its subdivision were established at an early stage.

scholarly journals Ice sheet scale subglacial meltwater conduit dimensions and processes: insights from 3D morphometry of a large sample of eskers

2021 ◽  
Author(s):  
Robert Storrar ◽  
Andrew Jones ◽  
Frances Butcher ◽  
Nico Dewald ◽  
Chris Clark ◽  
...  
Keyword(s):  
Numerical Models ◽  
Three Dimensional ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Process Models ◽  
Cross Sectional ◽  
Large Sample ◽  
Subglacial Environment ◽  
Depositional Processes ◽  
Subglacial Meltwater

<p>Meltwater exerts an important influence on ice sheet dynamics and has attracted an increasing amount of attention over the last 20 years. However, the active subglacial environment remains difficult to study mainly due to its inaccessibility. Understanding of the dimensions, pattern, and extent of subglacial meltwater conduits at the ice sheet scale is limited to relatively sparse observations. We address this gap by using the geomorphological record of Quaternary ice sheets as a proxy to quantify the dimensions and pattern of subglacial conduits at the ice sheet scale. We present the results of a high-resolution (2 m), large sample (n>50,000) study of three-dimensional esker morphometry at sample locations in SW Finland and Nunavut, Canada. Detailed mapping of esker crestlines and outlines permits the quantification of a number of parameters, including: length, width, height, cross-sectional area, volume, sinuosity, cross-sectional symmetry, and uphill/downhill trends. Whilst the dimensions of eskers reflect depositional processes as well as simply the size of the parent conduit, they nevertheless offer a powerful tool for understanding the size and shape of meltwater conduits and the configuration of subglacial drainage systems across large areas (entire ice sheets), and over long periods of time (from years to thousands of years) in both high spatial and temporal resolution. The results may be used to: (1) inform numerical models of subglacial meltwater drainage, (2) inform process models of esker formation, and (3) provide a dataset of esker morphometry against which other features may be compared (e.g. sinuous ridges on Mars).</p>

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.

COMPUTER MIGRATION OF OBLIQUE SEISMIC REFLECTION PROFILES

Geophysics ◽  
1975 ◽  
Vol 40 (6) ◽  
pp. 961-980 ◽  
Author(s):  
William S. French
Keyword(s):  
Seismic Reflection ◽  
Three Dimensional ◽  
Migration Velocity ◽  
Dimensional Structure ◽  
Two Dimensional ◽  
Reflection Data ◽  
Line Imaging ◽  
Geometrical Factors ◽  
Seismic Reflection Profiles

A reflecting interface with irregular shape is overlain by a material of constant velocity [Formula: see text]. Multifold reflection data are collected on a plane above the reflector and the reflector is imaged by first stacking then migrating the reflection data. There are three velocity functions encountered in this process: the measured stacking velocity [Formula: see text]; the true overburden velocity [Formula: see text]; and a profile migration velocity [Formula: see text], which is required by present point‐imaging migration programs. Methods of determining [Formula: see text] and, subsequently, [Formula: see text] are well‐known. The determination of [Formula: see text] from [Formula: see text], on the other hand, has not been previously discussed. By considering a line‐imaging migration process we find that [Formula: see text] depends not only on the true section velocity but also on certain geometrical factors which relate the profile direction to the structure. The relation between [Formula: see text] and [Formula: see text] is similar to, but should not be confused with, the known relation between [Formula: see text] and [Formula: see text]. The correct profile migration velocity is always equal to or greater than the true overburden velocity but may be less than, equal to, or greater than the best stacking velocity. When a profile is taken at an angle of (90−θ) degrees to the trend of a two‐dimensional structure, then the appropriate migration velocity is [Formula: see text] and is independent of the magnitude of any dips present. If, in addition, the two‐dimensional structure plunges along the trend at an angle γ, then the correct migration velocity is given by [Formula: see text]. The time axis of the migrated profile for the plunging two‐dimensional case must be rescaled by a factor of [Formula: see text], and structures on the rescaled profile must be projected to the surface along diagonal lines to find their true positions. When three‐dimensional data are collected and automatic three‐dimensional migration is performed, the geometrical factors are inherently incorporated. In that case, the migration velocity is always equal to the true velocity regardless of whether the structure is two‐dimensional, plunging two‐dimensional, or three‐dimensonal. Processed model data support these conclusions. The equations given above are intended for use in conventional migration‐after‐stack. Recently developed schemes combining migration‐before‐stack with velocity analysis give [Formula: see text] directly. In that case, the above equations provide a method of determining [Formula: see text] from [Formula: see text].

Delineating the Tuwu porphyry copper deposit at Xinjiang, China, with seismic-reflection profiling

Geophysics ◽  
2005 ◽  
Vol 70 (6) ◽  
pp. B53-B60 ◽  
Author(s):  
Tonglin Li ◽  
David W. Eaton
Keyword(s):  
Seismic Reflection ◽  
Porphyry Copper ◽  
Copper Deposit ◽  
Three Dimensions ◽  
P Wave ◽  
Seismic Profiles ◽  
Line Drawings ◽  
Geophysical Surveys ◽  
Out Of Plane ◽  
Seismic Reflection Profiles

The Tuwu deposit is one of a series of recently discovered porphyry copper deposits in the eastern Tian Shan range of Xinjiang, China. Since its discovery in 1997, more than ten boreholes have been drilled and a suite of geophysical surveys has been acquired to delineate the deposit. As part of the geophysical program, a set of eight seismic reflection profiles was acquired in 2000, followed by a physical rock-property study in 2001. The ores are characterized by slightly higher density (Δρ ∼ 0.1 g/cm[Formula: see text]) and significantly higher P-wave velocity ([Formula: see text] ∼ 1.0–1.5 km/s) than the dioritic host rocks. The seismic surveys used 0.6- to 0.9-kg shallow dynamite sources, with a 24-channel end-on spread and offsets up to 350 m. The orebody and associated igneous layers dip steeply (>45°) toward the south, so careful processing of the seismic data was required. Weak reflections from stratigraphic contacts are visible on most of the profiles, including the top of the intrusion and the base of the orebody. Since the observed reflections include a significant out-of-plane component, we developed a simple 2.5D migration procedure. This method was applied to line drawings of the seismic profiles, providing the basis for delineation of the orebody in three dimensions. Synthetic seismic sections computed using the inferred bounding surfaces of the ore deposit are in reasonable agreement with observed reflections, even for along-strike lines not used to build the model. The ability to verify interpreted reflections using line intersections was critical to the development of our model. The results of this work indicate that seismic methods may be useful as an aid for mapping the flanks of shallow, moderately dipping porphyry copper orebodies and associated strata, particularly for defining the structure of deeper sections of the mineralized zones in advance of drilling.

Seismic reflection constraints on imbrication and underplating of the northern Cascadia convergent margin

1996 ◽  
Vol 33 (9) ◽  
pp. 1294-1307 ◽  
Author(s):  
A. J. Calvert
Keyword(s):  
Continental Shelf ◽  
Seismic Reflection ◽  
Deep Structure ◽  
Vancouver Island ◽  
Cascadia Subduction Zone ◽  
Accretionary Wedge ◽  
Seismic Profiles ◽  
Outer Continental Shelf ◽  
E Region ◽  
Seismic Reflection Profiles

An interpretation of the deep structure of the continental shelf offshore southern Vancouver Island, subject to constraints from other geophysical data, is derived by combining seismic reflection profiles shot in 1989 with those from an earlier 1985 survey. Accretionary wedge sediments, which extend landward beneath the volcanic Crescent terrane, comprise two primary units, both of which have shortened through duplex formation. The maximum thickness of the Crescent terrane, 6–8 km, occurs just seaward of its contact with the inboard, largely metasedimentary Pacific Rim terrane. The E region of reflectivity, first detected dipping landward beneath Vancouver Island, is regionally extensive, being observed on all the seismic profiles. The E reflectivity thins seaward and splits into two or more strands that probably link into major faults within the accreted sedimentary wedge. Reflections from the interplate décollement beneath the outer continental shelf separate from the downgoing plate, continue into the deepest level of the E reflectivity, and are interpreted to represent a single décollement surface above which imbrication of accreted units occurred. It is proposed that at the southern end of Vancouver Island the E reflections represent mainly underthrust sediments above a former subduction décollement, both of which were incorporated into the overlying continent when the subduction thrust stepped down into the descending oceanic plate. This change in depth of the subduction thrust underplated one or more mafic units to the continent. The reflection from the top of the subducting Juan de Fuca plate appears to be around 5 km shallower farther north along the margin, indicating that the underplated region could be confined to the embayment in the Cascadia subduction zone.

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