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Fault-attributed Correlation lines

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__NOTOC__
{{OR/15/046}}
==Fault construction==
Faults can be constructed in both map and cross-section as fault linework. Where fault linework is created in the map these are referred to as '''Fault Trace '''objects; where fault linework is created in cross-section these are referred to as '''Fault Stick '''objects. Fault information is also attached to some map '''croplines '''and cross-section '''correlation lines'''.

===Fault Traces===
Fault traces represent the top of a fault plane in the map as a simple line. These lines serve mainly as a reference to the surface or subsurface expression of the top of the fault plane, and are used to associate a series of fault sticks together from cross-sections.

To draw a fault trace, pick the '''Fault '''code from the lower panel in the object tree '''Codes '''tab and use the pen or digitizing drawing tools to construct the line on the map.

[[Image:OR15046fig146.jpg|frameless|center|350px|]]
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[[Image:OR15046fig147.jpg|frameless|center|350px|]]

Fault trace networks can be constructed by snapping fault trace lines together. Simply drag the end node of a fault trace towards the other trace.

[[Image:OR15046fig148.jpg|frameless|center|350px|]]

===Fault Sticks===
Fault sticks represent the fault plane in cross-section. They are constructed much like a normal correlation line. To draw a fault stick, pick the '''Fault '''code from the lower panel in the object tree '''Codes '''tab and use the pen or digitizing drawing tools to construct the line in the cross-section.

[[Image:OR15046fig149.jpg|frameless|center|350px|]]

Positions where fault traces cross the section are shown as dashed vertical markers. This aids you in positioning of fault sticks to tie-in with the map traces.

[[Image:OR15046fig150.jpg|frameless|center|500px|]]

[[Image:OR15046fig151.jpg|frameless|center|500px|]]

Drag the top node of the fault stick towards the vertical marker to snap it.

[[Image:OR15046fig152.jpg|frameless|center|500px|]]

Note that fault sticks do not have to come up to the terrain profile — they can terminate within horizons. In the map view the top node of a fault stick is shown as a dot. If the stick reaches the terrain profile the dot will be red, if it terminates at depth it will be orange.

[[Image:OR15046fig153.jpg|frameless|center|350px|]]

Once fault sticks are constructed, correlation lines can be snapped to them, as described in general editing in the main Cross-Section Window part of this manual.

===Fault-attributed Croplines===
Croplines can honour faults in two ways;

====1 – Snap to fault trace====
Croplines can be snapped to fault traces in the map. This is not always desirable, depending on the nature of the geology however. Two scenarios where it '''''does '''''make geological sense are;

# Where the fault plane is exactly vertical
# Where the fault comes to the surface '''and '''the cropline is at outcrop

[[Image:OR15046fig154.jpg|frameless|center|350px|]]

====2 – Construct fault crop====
Where the cropline runs into the fault plane at depth it often makes no geometric sense to snap the cropline to the fault trace, especially if the fault plane is non-vertical. In these cases, construct a cropline to represent the crop of the horizon on the fault plane.

Consider the following map;

[[Image:OR15046fig155.jpg|frameless|center|350px|]]

Sketch the “fault crop” as two additional lines (implies the fault is dipping to the South East in this example).

[[Image:OR15046fig156.jpg|frameless|center|350px|]]

Join the croplines together by dragging their end nodes together.

[[Image:OR15046fig157.jpg|frameless|center|350px|]]

'''Right click '''on the cropline segments which run along the fault crop and choose '''Add Fault Crop Attribute'''. This flags the cropline as a “'''''fault crop'''''” — note that for this approach to work the croplines on the fault crop must be separate objects — if necessary, split down existing croplines to achieve this.

[[Image:OR15046fig158.jpg|frameless|center|350px|]]

Fault crop attributed cropline shows with red nodes to indicate fault crop;

[[Image:OR15046fig159.jpg|frameless|center|350px|]]

Completed linework for the blue horizon, showing two segments of fault crop (hangingwall and footwall crops), two other segments of normal cropline. Presence side seeds have been set here too (refer to editing croplines general section in the manual for more detail);

[[Image:OR15046fig160.jpg|frameless|center|350px|]]

Repeat for other horizons.

[[Image:OR15046fig161.jpg|frameless|center|350px|]]

If you need to drag the end of a cropline across a fault trace without it snapping, hold down the CTRL key as you drag.

===Fault-attributed correlation lines===
By snapping correlation lines to fault sticks in section you can start to build up the relationships and throws on the fault planes.

[[Image:OR15046fig162.jpg|frameless|center|500px|]]

Three sections above displayed as 3D linework in SKUA-GOCAD;

[[Image:OR15046fig163.jpg|frameless|center|500px|]]
[[Category: OR/15/046 BGS Groundhog® Desktop Geoscientific Information System External User Manual | 07]]

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Ajhil: /* Fault-attributed Correlation lines */