Seismic section

Since faults are zones of inherent weakness they may be reactivated over geologic time. Usually, faulting occurs well after the sediments have been deposited. An exception to this is a growth feu/f (also termed a syn-sedimentary fault), shown in Figure 5.7. They are extensional structures and can frequently be observed on seismic sections through deltaic sequences. The fault plane is curved and in a three dimensional view has the shape of a spoon. This type of plane is called listric. Growth faults can be visualised as submarine landslides caused by rapid deposition of large quantities of water-saturated... 

Of particular interest in Figure 4-292 is the shaly sandstone in the 690-720-ft interval. In this zone, the LWD sonic measurements are consistently faster than the wireline measurements. Since the wireline logs were acquired 10 days after drilling, it is likely that shale swelling in the shaly sandstone has taken place. This phenomenon, known as formation alteration, causes the wireline sonic measurements to be slower. In this type of zone, LWD sonic yields a more correct At, which will better match surface seismic sections. 

Fig. 8. interpreted refiection-seismic section from Venezuela, earned out in the period 1939-1941, showing the limited resolution in the period prior to the 1960s (from LeRoy, 1951). 

Fig. 8. This figure shows a cross-section of the effective stress, in psi, versus two way time over a prospect in the deepwater. Gulf of Mexico. A pressure cell is clearly visible, which is bounded by salt on the left hand side. The discovery well location through the bright spots is also noted on the seismic section.

It was shown earlier that there is some discussion over the composition of the lower continental crust and whether it is felsic or basaltic. One possible solution is that lower continental crustal compositions have changed with time. Durrheim and Mooney (1991, 1994) studied seismic sections through Archaean and Proterozoic cratons and suggested that Archaean continental crust is between 27 and 40 km thick and has a thin mafic layer at its base, making up between 5 and 10% of the total crustal thickness. In contrast Proterozoic crust is between 40 and 55 km... 

Fig. 18. The same line of traverse as shown in Fig. 16, illustrating the variable synthetic seismic response over the major calcite-cemented zones (arrows) in the Lower Namur Sandstone. Note that where the calcite-cemented zones are thickest (Gidgealpa-23) two peaks are produced which are separated by a broad trough. In contrast, where only a relatively thin carbonate-cemented zone is present (Gidgealpa-17) only a small peak is produced. The gross carbonate-cemented interval is mappable on seismic sections below the C horizon (top Cadna-Owie Formation).

It is important to realize that small faults which may be important with respect to fluid flow properties can be in some cases easily overlooked in cores or thin sections (Sverdrup Bjorlykke 1992). It is generally assumed that in the Halten Terrace most of the faulting occurred pene-contemporaneously with the rifting in the Upper Jurassic. Most of the faults seen on seismic section only extend into the base Cretaceous... 

The status of the faults in such a situation, however, is not a simple matter, as structural elements like faults in sedimentary basins have physical and chemical attributes that influence fluid dynamics, and which are best understood in the context of sedimentary poroperm and diagenetic mineral reaction kinetics and thermodynamics. Faults appear as geometrical phenomena, seen as lines on seismic sections or planes in 3D modelling but are in reality complex. 

Kokkalas S, Kamberis E, Xypolias P, Sotiropoiilos S, Koukouvelas I (2013) Coexistence of thin- and thiek-skinned tectonics in Zakynthos area (western Greece) insights from seismic sections and regional seismicity. Tectonophysics 597-598 73-84... 

Fig. 1. [Reproduced in colour in Plate 1 on page 421.] Seismic section showing one example of a reflection termination surface or sequence boundary. Reflection termination surfaces are the boundaries of seismic bodies.

Reflection-Free Areas. Reflection-free textures on seismic sections indicate large igneous masses (e.g. buried volcanoes), salt features or shales. 

Fig. 1. A seismic section showing three different textures. The ovals mark regions of interest.

Harris Corner Detector Applied to Seismic Sections... 

Figure 1 shows an example of a sparse extrema representation of a seismic section, illustrating the cube containing amplitude values. All events from the original seismic section are preserved in the extrema value cube, but are represented only through the position of its minimum or maximum. 

Fig. 2. Reconstruction of a single trace from a seismic section. Image (a) shows the seismic section, with the seismic trace marked with white. The plots in (b) show the seismic trace (solid curve) and corresponding reconstructions (dashed curves). The number of attributes applied in the reconstructions increases from left to right.

D visualization is imperative to the analysis tool. Figure 5 shows an example of 3D visualization of extracted surfaces from a field offshore mid Norway. The horizontal slice is an enhanced attribute produced by the ant tracking, mapping all extracted surfaces, and a transparent seismic section. More about applying the fault interpretation workflow on this data can be found in [8]. 

Fig. 5. The fault surfaces can be displayed as 2D lines on seismic or attributes, or as 3D patches by double clicking on the 2D lines. A seismic section and a fault attribute slice from the main field example are displayed together with the fault surfaces.

Fig. 15. Seismic section containing two sait domes. The framed region is shown in greater detail in Figure 17.

The seismic section of the Safety Evaluation Report (SER) has been divided into seven subsections Geology, Seismic Ground Motion, Geotechnical Engineering and Site Soil Conditions, System Response to Seismic Motion, Structures and Foundations, Piping, and Equipment. 

Demonstrate that structural integrity of the CWS is maintained under normal and abnormal load conditions using applicable codes, standards, and analysis methods, including those specified in the seismic section of the SER. Components which are part of the CWS shall be subject to ... 

This restart criterion requires that WSRC demonstrate the structural safety margins stated in the Safety Analysis Report (SAR) are consistent with current plant configuration and will be maintained. These margins should be consistent with the national codes and standards pertaining to seismic (discussed in the seismic section of the SER) and other postulated design basis accidents. 

The ECS is designed to prevent fuel melting for worst case single failure accidents. Full ECS flow to the reactor is required within 20 seconds after an actuation signal is received or when plenum inlet pressure reaches 90 psi (at approximately 20 seconds for a large break LOCA). Seismic qualification of the ECS is addressed in the Seismic Section of the SER. 

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