Structure Geology

Structure Geology

Structure Geology as the name indicates it is related to structures. What kind of structures are to be observed in this field?.
The basic structures that is often used are

• Faults 
• Folds 

Faults

Faults are defined as the displacement or the movement in the rocks that make up the Earth's crust.

Figure 1. Fault in the Earth's crust.

As shown in the figure 1 the arrows indicate the movement of the rocks, the movement is referred as comparative movement. there are different types of fault's as further divided by the way of displacement.
The block that moves relative to another is the hanging-wall and the block which is static at it's position is the foot wall. The foot wall can Move upward and downward. So the fault as divided are by this movement.
When hanging-wall moves downward with respect to action of gravity of the above burden it is called normal fault. And the hanging wall upward movement is called reverse fault as is against the gravity.
The major division of the faults are strike-slip and dip-slip
Strike slip faults are along strike so in order to understand the strike slip 1st strike should be known.
Strike is the line which is at right angle to the dip direction. Strike is formed by the intersection of dip direction and imaginary line that run along the horizontal surface.

Figure 2. Strike and dip directions are shown.

So strike slip faults are called transform faults their movement is along strike and pass one another.

Figure 3. On the lower left is reverse fault and to the right is strike slip or transform fault.

Dip-slip faults includes normal and reverse fault. Once again had to acknowledge that normal faults are those which moves according to the gravity action and reverse faults are those which moves anti-gravity. These faults are the reason for the earthquakes. When movement of the two Earth crust block trigger it rubs against each other and as their are solid rocks, they are rough and keeps the crust intact so their movement triggers earthquake.

Folds

Folds are the structures that are formed due to plate movements. Faults are also responsible in its forming. These are the folded starta of the Earth's crust the fold are formed when originally horizontal strata as deposition is always horizontal it is curved or bent, deformation in the strata due to forces.

Figure 4. Component of fold.

Fold are basically the deformation and it occurs when forces on both sides, somewhere the forces have to be accommodated so the strata where it can bend, forms the fold. There are types of folds anticline and syncline.
Anticline is shown in the figure 4 it is the convex upward fold. In it's inner part, lowest one will have the older rocks as it is the core and younger on the limbs and hinge. the syncline is the vice-versa. It will be concave upward and in the core the inner portion will have the younger rocks the limbs will have older rocks.