Tensional Forces

Imagine you are pulling apart a chocolate bar slowly with both hands. At first, tiny cracks appear, and then—snap!—it breaks along a jagged line. Now, replace the chocolate with the Earth’s crust, and what you have just witnessed is a process called crustal fracture.

Deep within the Earth, tremendous forces are always at play, shaping the land we live on. Among these, tensional forces play a key role in pulling apart large sections of the crust, creating fractures, faults, and even reshaping entire landscapes over millions of years.

Crustal Fracture

The Earth’s crust is not a single unbroken shell; instead, it’s made of large rock masses that are continuously stressed by internal forces. When these forces pull apart (tensional forces) or push together (compressional forces) beyond the rock’s ability to bend, something dramatic happens—the crust breaks.

This breaking and displacement of rock along a plane is called a crustal fracture.

• If there is no significant movement along the break, it is simply a fracture or a joint.
• If the rocks actually move along the fracture, it is called a fault.

Faults and Their Types

When the crustal rocks are displaced, due to tensional movement caused by the Endogenetic forces along a plane is called fault & that plane is called fault plane.

These movements define the different types of faults.

1. Normal Fault

This occurs when tensional forces stretch the crust apart, causing one block of rock to drop downward relative to the other.

Effect: The area between the fault lines extends (becomes wider).

📍 Example: The Great Rift Valley in Africa is a classic case of a normal fault where the land is literally being pulled apart.

2. Reverse Fault

Here, if you see at the figure it seems compressional forces push two blocks towards each other, forcing one to rise over the other.

🚨 But wait! Shouldn’t compression create folds instead of faults?

Good question! Normally, compression bends rock layers into folds, but if the rocks are already fractured, they cannot bend anymore. Instead, one block thrusts over the other, creating a reverse fault.

Effect: The land shortens and becomes more compact.

📍 Example: The Himalayas were formed due to massive reverse faulting as the Indian Plate pushed into the Eurasian Plate.

3. Strike-Slip Fault (Lateral Fault)

Now, imagine two people walking side by side, but suddenly one moves ahead while the other lags behind. This sideways displacement is what happens in a strike-slip fault.

Here, the rock blocks move horizontally past each other instead of moving up or down.

Depending on the direction of movement, these faults can be:

• Left-lateral (Sinistral): If the block on the far side moves to the left.

• Right-lateral (Dextral): If the block on the far side moves to the right.

Real-World Analogy: Imagine placing your hands together and rubbing them in opposite directions—your hands remain level, but they slide past each other.

📍 Example: The San Andreas Fault in California, which is responsible for many earthquakes in the region, is a classic strike-slip fault.