Fault planes

Similar conclusions can be formed by studying the results of Bursill, Netherway, and Grey They examined the situation in rutile, Ti02- Instead of calculating the 

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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... 

A secondary feature is the development of rollover anticlines which form as a result of the downward movement close to the fault plane which decreases with increasing distance from the plane. Rollover anticlines may trap considerable amounts of hydrocarbons. 

Clay smear soft clay, often of marine origin, is smeared into the fault plane during movement and provides an effective seal. 

Diagenetic Healing late precipitation of minerals on or near the fault plane has created a sealing surface (see diagenesis for more detail). 

Cataclasis the fault movement has destroyed the rock matrix close to the fault plane. Individual quartz grains have been ground up creating a seal comprising of rock flour . 

This kind of pressure solution / precipitation is active over prolonged periods of time and may almost totally destroy the original porosity. Precipitation of material may also occur in a similar way on the surface of fault planes thus creating an effective seal via a process introduced earlier as diagenetic healing. 

Verwerfimg, /. rejection (Aftnin ) disloca tion, throw, slip, fault, faulting. Verwerfungs-flache, /. Qeol.) fault plane. 

Dip—ihe angle the fault plane makes with the horizontal, measured from the horizontal to the fault plane. 

Strike—di line on the horizontal surface represented by the intersection of the fault plane and the horizontal surface. The strike line is always horizontal, and since it has direction, it is measured either by azimuth or bearing. Strike is always perpendicular to the dip. 

Slip—[ c actual linear movement along the fault plane. 

Fault traps—involve the movement of the reservoir rock formation to a position where the formation across the fault plane provides a seal preventing further migration of hydrocarbons (see Figure 2-48). 

Regarding the development of a structural model of the refinery subsurface, it was observed that the discontinuities present in the area can be grouped into three distinct systems. With the exception of stratification (primary discontinuity), all three of these systems are represented by joints (fractures where the two opposing faces do not shift with respect to one another), shear joints (where the two faces do shift with respect to one another) and faults (fault planes or zones, marked by cataclasis, rubble and mylonite with clear evidence of shifting of the two faces). 

Site 997 was drilled at the crest of the Blake-Bahama Ridge (where the strongest BSR occurs) at 450 mbsf. One large solid piece of gas hydrate was recovered from approximately 331 mbsf at a suspected small fault plane. However, the presence of more disseminated hydrates was inferred over a zone from approximately 180 to 450 mbsf. It was indicated that gas hydrate development may be extensive at this location, possibly acting as a means of sealing with permeability and porosity reduction. 

Stacking faults are characterised by a fault plane and a fault displacement vector. On one side of the fault plane, the atoms that are located fer from the fault are displaced by a vector R in relation to the positions they would occupy in the absence of the fault. Strain fields emanating from any reconstructive bonding that is present near the fault plane will lead to additional displacements for atoms near the fault plane. Thus, the specification of R determines the positions of the atoms that are sufficiently distant so that the strain field generated by the fault is below some specified tolerance. For a planar fault, R may be determined experimentally by analysis of the diffraction contrast obtained with different diffraction vectors g. The positions of atoms near the fault may be determined theoretically by total energy minimisation calculations. Knowledge of these positions is essential to determine the electronic structure of the fault. 

FIGURE 2 Stacking sequence and associated stacking fault displacement vectors for three types of basal plane stacking fault in GaN. The double lines indicate the fault plane. The stacking fault vectors are shown for each fault. 

Fault plane layers in a crystal structure at which defect(s) arrangements in the normal stacking of the layer can occur... 

Silanation reaction of silane (SiELi) with OH groups Sorption uptake of liquid or gas by a microporous material Space-filling spatial arrangement of polyhedra such that each polyhedron shares all its faces with other polyhedra Stacking fault misalignment of layer(s) arising from a fault plane... 

Field and optical microscope studies showed that the fault plane is defined by a 2-3 cm wide cataclastic zone that is bounded laterally by a 1-3 m envelope of plastic and cataclastic deformation. Outside this envelope, the quartz microstructures displayed no evidence of significant deformation. Quartz in the fault envelope contains well-developed deformation bands, deformation lamellae, and intragranular healed fractures, which are visible at all scales of observation. 

The spatial distribution of plastic deformation adjacent to the fault plane can be explained by a model in which the propagating fault is preceded by a zone of stress concentration at its tip. Calculations by Blenkin-sop and Drury (1988) indicate that, for remote applied stresses of less than 100,MPa, the zone of stress concentration, with stress greater than 145 MPa, will have a lateral width of 1-3 m once the initial fracture is longer than 12 m. The high stresses estimated from the quartz microstructures adjacent to the fault are consistent with a low average stress in the crust because very high transient values of stress may occur locally, particularly at the propagating termination of fractures, shear zones, and folds. 

Thrust fault— A I ow-angle reverse fault in which the dip of the fault plane is 45° or less and displacement is primarily horizontal. 

There are some comments to make here. First, the positions of the Sn, Pb, or Ba atoms in these phases is not known, so that for these compounds the model must be regarded as hypothetical. Secondly, it does not suit needle-shaped crystals, as the first layer laid down must already include the fault planes inherently contained within it. This point will be returned to later. Thus the alkali-metal intergrowth phases, which are needle shaped, do not fall into this class. This growth mechanism can also be applied to the barium ferrites, which are plate-like crystals that form from a molten flux, and it is possible that it could account for the sort of faulting noted in the amphibole chain minerals described on p. 135 et seq. 

Other illustrations could be given. However, we have taken this model far enough for the present purposes, and ultimately it should be regarded as hypothetical. Careful comparison with experiment is needed to elucidate matters further. The purpose of the preceding discussion is simply to point out that interactions between fault planes and elaborate solid-state rearrangements involving a flux of point defects are not necessary in order to produce some of the seemingly complex structural sequences illustrated in this review. 

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