Seismic studies of the crust under the Williston Basin

1987 ◽  
Vol 24 (11) ◽  
pp. 2160-2171 ◽  
Author(s):  
E. R. Kanasewich ◽  
Z. Hajnal ◽  
A. G. Green ◽  
G. L. Cumming ◽  
R. F. Mereu ◽  
...  
Keyword(s):  
Seismic Refraction ◽  
Three Dimensional ◽  
Good Evidence ◽  
Dimensional Structure ◽  
Williston Basin ◽  
Mobile Belt ◽  
Low Velocity ◽  
Reflection Data ◽  
Yield Information ◽  
Seismic Recording

The seismic refraction method was used in 1981 to study the crust under the northern half of the Williston Basin, in Saskatchewan. A new method of spatial seismic recording, based on a triangular arrangement of receivers, was used for the first time to obtain three-dimensional structure and velocity information. The broadside seismic refraction and wide-angle reflection data obtained by the technique were of particular value in defining several faulted blocks. These blocks are also characterized by aeromagnetic anomalies trending in a northerly direction. The crustal thickness in the southern part of the western provinces shows large variation ranging from 35 to 50 km. Much of the area is also notable for the presence of one or more low-velocity layers and a high-velocity lower crust. There is good evidence for significant lateral heterogeneity, and detailed deep seismic reflection and refraction studies would likely yield information on dips and strikes of beds and faults around the basin as well as define the properties of the various terranes of the Hudsonian mobile belt.

Broadside wide-angle seismic studies and three-dimensional structure of the crust in the southeast Canadian Cordillera

1997 ◽  
Vol 34 (8) ◽  
pp. 1156-1166 ◽  
Author(s):  
M. J. A. Burianyk ◽  
E. R. Kanasewich ◽  
N. Udey
Keyword(s):  
Signal To Noise Ratio ◽  
Seismic Refraction ◽  
Three Dimensional ◽  
Dimensional Structure ◽  
High Signal ◽  
Canadian Cordillera ◽  
Wide Angle ◽  
Low Velocity ◽  
Seismic Properties ◽  
High Degree

Broadside, or fan, recordings of a Lithoprobe seismic refraction – wide-angle reflection experiment in the southeastern Canadian Cordillera show several features further illuminating the crustal structure beyond that previously derived from SCoRE '90 (Southern Cordillera Refraction Experiment of 1990) in-line data. Analysis of a nearly in-line profile centred on Castlegar, British Columbia, shows lower velocities in the upper crust associated with the Purcell Anticlinorium as well as velocity variations that may have some association with the Purcell fault zone. The depth to Moho is almost 38 km, somewhat deeper and on trend with the structure that has been established farther north. The broadside records show high signal-to-noise ratio PmP arrivals (i.e., reflections from the bottom of the crust). These PmP fan picks were analysed in regions away from in-line profiles, providing further measurements of the depth to Moho in the southeastern Cordillera. The analysis of the broadside records combined with the earlier in-line interpretations as well as older crustal seismic measurements make up a relatively high resolution database, compared with most other regions in Canada, from which we have generated maps of depth to Moho and average crustal velocity in the southeastern Cordillera of Canada. The maps show thin, low-velocity crust over much of the region and indicate a high degree of correlation between current crustal seismic properties and regional isotherms.

Periodic motion embedded in plane Couette turbulence: regeneration cycle and burst

2001 ◽  
Vol 449 ◽  
pp. 291-300 ◽  
Author(s):  
GENTA KAWAHARA ◽  
SHIGEO KIDA
Keyword(s):  
Periodic Motion ◽  
Temporal Structure ◽  
Three Dimensional ◽  
Dimensional Structure ◽  
Navier Stokes ◽  
Low Velocity ◽  
Mean Velocity ◽  
Navier Stokes Equation ◽  
Time Periodic Solutions ◽  
Regeneration Cycle

Two time-periodic solutions with genuine three-dimensional structure are numerically discovered for the incompressible Navier–Stokes equation of a constrained plane Couette flow. One solution with strong variation in spatial and temporal structure exhibits a full regeneration cycle, which consists of the formation and breakdown of streamwise vortices and low-velocity streaks; the other one, of gentle variation, represents a spanwise standing-wave motion of low-velocity streaks. These two solutions are unstable and the corresponding periodic orbits in the phase space are connected with each other. A turbulent state wanders around the strong one for most of the time except for occasional escapes from it. As a result, the mean velocity profile and the root-mean-squares of velocity fluctuations of the plane Couette turbulence agree very well with the temporal averages of those of this periodic motion. After an occasional escape from the strong solution, the turbulent state reaches the gentle periodic solution and returns. On the way back, it experiences an overshoot accompanied by strong turbulence activity like an intermittent bursting phenomenon.

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].

Seismic refraction observations north of the Brownson Deep*

1952 ◽  
Vol 42 (4) ◽  
pp. 291-306
Author(s):  
J. B. Hersey ◽  
Charles B. Officer ◽  
H. R. Johnson ◽  
S. Bergstrom
Keyword(s):  
High Speed ◽  
Seismic Refraction ◽  
Low Frequency ◽  
Good Evidence ◽  
Constant Frequency ◽  
Reflected Waves ◽  
Surface Reflection ◽  
The North ◽  
Reflection Data ◽  
Compressional Velocity

Abstract Results of several refraction profiles made on the rise to the north of the Brownson Deep are presented. Good evidence for a high-speed layer with travel-time curves showing a compressional velocity of 7.94 km/sec. and an intercept of 8.4 sec. is presented, and the presence of an overlying lower-speed layer (6.64 km/sec., intercept 8.1 sec.) is demonstrated on less complete evidence. Neither layer correlates with existing reflection data in the area. Two sets of secondary low-frequency arrivals are tentatively interpreted as a refracted shear wave and a wave that has taken a bottom and surface reflection and then a basement refraction. Evidence is presented for a newly observed forerunner of the refracted-surface reflected waves of the permanent sound channel (RSR waves) consisting of a train of nearly constant frequency waves which appear to travel between surface and bottom via the RSR path and along the bottom at the speed of sound in water at the bottom.

Interpretation of three-dimensional seismic refraction data from western Hecate Strait, British Columbia: structure of the Queen Charlotte Basin

1993 ◽  
Vol 30 (7) ◽  
pp. 1427-1439 ◽  
Author(s):  
J. A. Hole ◽  
R. M. Clowes ◽  
R. M. Ellis
Keyword(s):  
Tectonic Evolution ◽  
Seismic Reflection ◽  
Three Dimensional ◽  
Strike Slip ◽  
Dimensional Structure ◽  
Three Dimensional Structure ◽  
Queen Charlotte Islands ◽  
Reflection Data ◽  
Basement Depth ◽  
Refraction Data

The Queen Charlotte Basin consists of up to 6 km of Tertiary clastic sediments in a complex sequence of fault-bounded subbasins. The tectonic evolution of the basin in still being debated, with recent interpretations including distributed strike-slip extension, oblique or en echelon rifting, simple extension orthogonal to the plate margin, and block faulting and vertical tectonics. A combined seismic reflection and refraction survey was carried out in 1988 to investigate the structure and tectonic evolution of the basin and underlying crust. While the marine multichannel reflection data were being collected, refracted and wide-angle reflected energy from the large air-gun array was recorded at surrounding land sites in both two-dimensional (in-line) and three-dimensional (broadside) geometries. The broadside refraction data recorded on the Queen Charlotte Islands provide good three-dimensional coverage of western Hecate Strait. These data are modelled to determine the three-dimensional structure of the Queen Charlotte Basin. The reflection data indicate that the sedimentary Queen Charlotte Basin beneath the shotpoints varies rapidly in thickness and is highly three-dimensional. First-arrival traveltimes from the broadside refraction data are inverted to find the three-dimensional structure of the basement interface beneath the shots and out of the planes of the reflection sections. A map of basement depth is derived for a region several kilometres wide adjacent to the reflection lines. Basin thickness varies rapidly between ~ 200 m and ~ 6 km. The model is consistent with the seismic reflection and potential field data sets. Although most of the basin is modelled as sediments overlying rocks with crustal velocities, a thick sequence of interbedded sedimentary and volcanic rocks is interpreted to underlie the shot lines in one region that lies east of the central Queen Charlotte Islands. Four major faults are also interpreted. These are based on sharp vertical relief of over 2 km on the map of basement depth. The orientation and topography across the faults and the small lateral scale and large topographic changes of the subbasins support the distributed strike-slip extension evolutionary model for the basin.

Modeling of zero-offset reflection profiles with asymptotic ray theory

1981 ◽  
Vol 18 (3) ◽  
pp. 551-560
Author(s):  
George A. McMechan
Keyword(s):  
Seismic Reflection ◽  
Constant Velocity ◽  
Seismic Refraction ◽  
Drill Core ◽  
Ray Theory ◽  
Low Velocity ◽  
Tectonic Structures ◽  
Seismic Reflection Data ◽  
Reflection Data ◽  
Zero Offset

Synthetic reflection profiles computed by asymptotic ray theory can be used in the interpretation of laterally varying tectonic structures. The algorithm is implemented for normally incident (zero-offset) rays in two-dimensional models that are specified in terms of constant velocity layers separated by piecewise cubic boundaries. Applications include modeling of profiles containing lenses, interbedded high- and low-velocity layers, and oceanic ridges. The method is practical and flexible in the sense that structural, lithologic, drill core, and seismic refraction constraints can be directly combined with the seismic reflection data.

Effects of three‐dimensional structure on magnetotelluric sounding curves

Geophysics ◽  
1983 ◽  
Vol 48 (10) ◽  
pp. 1402-1405 ◽  
Author(s):  
Stephen K. Park ◽  
Arnold S. Orange ◽  
Theodore R. Madden
Keyword(s):  
Surface Layer ◽  
Three Dimensional ◽  
Dimensional Structure ◽  
Two Dimensional ◽  
Regional Structure ◽  
One Dimensional ◽  
Three Dimensional Structure ◽  
Regional Effects ◽  
Yield Information ◽  
Geologic Map

Significant errors may result when applying one‐dimensional (1-D) or two‐dimensional (2-D) interpretation methods to magnetotelluric (MT) data collected in three‐dimensional (3-D) environments. Both depths and resistivities can be grossly incorrect if 1-D or 2-D methods are applied in a 3-D setting. We present examples of MT sounding curves generated using a 3-D modeling program (Madden and Park, 1982) and illustrate some interpretation pitfalls if 3-D effects are not considered. The 3-D effects discussed herein are attributed to a surface layer heterogeneity, and can be readily identified in MT data from a well‐designed MT survey. The MT survey must include stations chosen to yield information about regional structure. Alternatively, carefull examination of a geologic map will help the intepreter estimate the regional effects present in the data.

Sign in / Sign up

Export Citation Format

Share Document