Fault terminology (R.P – 8.3.1.3, 8.3.1.2)
A fault is a break in the Earth’s crust along which there is or has been discernible movement. Displacement along faults can vary from a few millimeters to several hundred miles. Some faults move blocks up or down, others move blocks laterally over one another, and others move blocks laterally to slide by each other.
Faulting is an important adjunct to structural deformation because it establishes the orientations of stress directions that develop the geometry of tectonic provinces and facilitates their exploration.
The angle that a fault plane makes with the horizontal is the dip of the fault plane. Fault plane dips vary from vertical to horizontal and are oriented in response to the stress field in which they form.
The strike of a fault plane is represented by the line of intersection between the fault and horizontal surface. Strike line is always horizontal and since it has direction, is measured either by azimuth or bearing.
Horizontal movement component of a fault is known as the heave of the fault. The throw of a fault is the vertical movement component of its displacement. Both heave and throw are variable with movement along the fault and the dip of the fault plane.
| Fig. 50 Fault anatomy |
The hanging wall of a fault is located above the fault surface and bears upon it. The footwall of a fault is beneath the fault. It occupies the position beneath the fault regardless of whether the hanging wall has moved up or down.
Compression is usually responsible for reverse faulting where the hanging wall is moved up relative to the footwall. A reverse fault that dips 30 or less becomes a thrust fault.
Strike-slip faults occur where crustal blocks slide laterally by each other along nearly vertical zones of movement.
| Fig. 51 Three types of fault motion |
Strike-slip faults are referred to in many ways, including wrench, tear, and transcurrent faults. They are identified by the sense of movement of the block on the far side of the fault from the viewer. If the viewer is observing the fault and the block on the far side of the fault has moved to the right, the fault is known as a right-lateral strike-slip fault. Right lateral faults are also known as right-slip, right-handed or dextral strike-slip faults. Faults with left-handed displacement are referred to with similar nomenclature. However, left-handed faults are sinistral, as opposed to dextral or right-handed faults. ( Абрамова Р . Н ., Квеско Н . Г ., Introduction to Continuum Mechanics- учебное пособие , Томск , ТПУ . 2005.)
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EXERCISES
1. Match the English term with the Russian variant. (TEXT: Fault
terminology)
1. fault a. сдвиг
2. normal fault b. простирание
3. reverse fault c. висячий блок
4. throw d. косой, наклонный
5. heave e. сброс
6. hanging wall f. наклон, падение
7. footwall g. взброс
8. dip h. горизонтальная амплитуда смещения
9. strike i. лежачий блок
10. strike-slip fault j. вертикальная амплитуда смещения
11. oblique k. разлом, разрыв
2. Re-read the text “Fault terminology”. Look at the diagram (anatomy of a fault). Label the letters and give an explanation. (R.P – 8.3.1.2)
Match the term with its definition and then find its translation.
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