Question

• Explain how rocks respond to those stresses within the Earth's crust by brittle, elastic, or plastic deformation, or by fracturing
• Summarize how rocks become folded
• Describe the conditions under which rocks fracture
• Briefly describe the different types of faults, including normal, reverse, thrust, and strike-slip

Answer 1

2. How rocks become folded. - wave like bends are formed in the crustal rocks due to tangential compressive force resulting from horizontal movement caused by the endogenetic force originating deep within the earth. Such bends are called folds wherein some parts are bent up and some parts are bent down. The upfolds are called anticlines and downfolds are called synclines.

3. The crustal fracture is the main reason why rocks undergo fault or fractures, depending on the intensity of the force and the direction of the force acting on the rock. Generally fractures are divided into joints and faults.

• JOINT - it is defined as a fracture in the crustal rocks wherein no appreciable movement of rock takes place.
• FAULT - here appreciable displacement of the rocks on both sides of a fracture , which is also parallel, takes place.

4. Types of faults :

• Normal faults - displacement of rocks blocks in the opposite direction due to fracture consequent upon greatest stress. fault plane is usually between 45 degrees and the vertical.
• Reverse fault - movement of both fractured rock blocks towards each other. It is usually inclined between 40 degrees and the horizontal.
• Lateral / strike slip fault - rock blocks are displaced horizontally along the fault plane.
• Step faults - when a series of faults occur in any area in such a way that the slopes of all the fault planes of al the faults are in the same direction, the resultant faults are called step faults.