Understanding Rock Fractures and Movement in Earth's Crust

The question describes a geological process involving rocks within the Earth's crust that undergo fracturing, followed by the movement of the rock masses on either side of the fracture in different directions. This specific geological feature is a key concept in structural geology.

Defining Geological Features

Let's look at the terms provided in the options to understand what each one represents in geology:

• Fold: A fold is a bend in layers of rock, usually resulting from compression. It's a plastic deformation rather than a brittle fracture with movement along the break.
• Joint: A joint is a fracture or crack in rock along which there has been little or no movement. It's a break without significant displacement of the rock masses.
• Fault: A fault is a fracture or zone of fractures between two blocks of rock. Faults allow the blocks to move relative to each other. This movement can be sudden (causing earthquakes) or gradual (creep). The key characteristic is significant displacement along the fracture plane.
• Crack: 'Crack' is a general term for a break. While a fault is a type of crack, the term 'fault' is specifically used in geology when there is displacement along the fracture surface in the Earth's crust.

Analyzing the Question's Description

The question states: "When rocks fracture in earth crust and again the same rock masses move in different directions". This description precisely matches the definition of a geological fault. The fracture is created, and then the rock blocks on either side move relative to each other along this fracture plane.

Based on the definitions, the geological feature where rock masses fracture and move in different directions along the fracture is a fault.

Conclusion

The phenomenon where rocks fracture in the Earth's crust, and the rock masses move relative to each other along the fracture, is known as a fault.

Revision Table: Rock Fracture & Movement

Here's a quick review of the key terms:

• Fault: Fracture with relative movement of rock blocks.
• Joint: Fracture with little to no movement.
• Fold: Bending of rocks without fracturing or movement along a break.

Additional Information: Types of Faults

Faults are fundamental structures in the Earth's crust. They are classified based on the direction of relative movement:

• Normal Fault: The hanging wall moves down relative to the footwall. This occurs under tensional stress.
• Reverse Fault: The hanging wall moves up relative to the footwall. This occurs under compressional stress. If the dip angle is low, it's called a Thrust Fault.
• Strike-Slip Fault: Rocks move horizontally past each other. This occurs under shear stress. Examples include the San Andreas Fault.

Faults are important because they are often associated with earthquakes, as sudden slips along fault planes release energy.