Three-dimensional structure from feathered two-dimensional marine seismic reflection data: The eastern Nankai Trough

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].

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

Canadian Journal of Earth Sciences ◽

10.1139/e93-123 ◽

1993 ◽

Vol 30 (7) ◽

pp. 1427-1439 ◽

Cited By ~ 6

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.

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Three-Dimensional Structure of Cloned T3 Connector Protein at 1.6nm Resolution

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100180161 ◽

1990 ◽

Vol 48 (1) ◽

pp. 282-283

Author(s):

José L. Carrascosa ◽

José M. Valpuesta ◽

Hisao Fujisawa

Keyword(s):

Dna Sequences ◽

Expression Vector ◽

Three Dimensional ◽

Deae Cellulose ◽

Dna Packaging ◽

Dimensional Structure ◽

Two Dimensional ◽

Freezing And Thawing ◽

Three Dimensional Structure ◽

Dimensional Reconstruction

The head to tail connector of bacteriophages plays a fundamental role in the assembly of viral heads and DNA packaging. In spite of the absence of sequence homology, the structure of connectors from different viruses (T4, Ø29, T3, P22, etc) share common morphological features, that are most clearly revealed in their three-dimensional structure. We have studied the three-dimensional reconstruction of the connector protein from phage T3 (gp 8) from tilted view of two dimensional crystals obtained from this protein after cloning and purification.DNA sequences including gene 8 from phage T3 were cloned, into Bam Hl-Eco Rl sites down stream of lambda promotor PL, in the expression vector pNT45 under the control of cI857. E R204 (pNT89) cells were incubated at 42°C for 2h, harvested and resuspended in 20 mM Tris HC1 (pH 7.4), 7mM 2 mercaptoethanol, ImM EDTA. The cells were lysed by freezing and thawing in the presence of lysozyme (lmg/ml) and ligthly sonicated. The low speed supernatant was precipitated by ammonium sulfate (60% saturated) and dissolved in the original buffer to be subjected to gel nitration through Sepharose 6B, followed by phosphocellulose colum (Pll) and DEAE cellulose colum (DE52). Purified gp8 appeared at 0.3M NaCl and formed crystals when its concentration increased above 1.5 mg/ml.

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