Question

An assertion (A) and a reason (R) are given below. Choose the correct option.

Assertion (A): Transform boundaries often cause strong earthquakes.

Reason (R): In these regions, as two plates slide past each other, a large amount of pressure builds up in the rocks, which is then suddenly released.

• A. Both A and R are true, but R is not the correct explanation of A.
• B. A is true, but R is false.
• C. A is false, but R is true.
• D. Both A and R are true, and R is the correct explanation of A.

Answer 1

Answer:

D. Both A and R are true, and R is the correct explanation of A.

Plate Tectonics and Earthquakes

The Earth's lithosphere is divided into several tectonic plates that move relative to each other. The boundaries where these plates interact are zones of significant geological activity, including earthquakes and volcanic eruptions.

Types of Plate Boundaries

• Divergent Boundaries: Plates move apart, creating new crust. Example: Mid-Atlantic Ridge.
• Convergent Boundaries: Plates move towards each other. This can lead to subduction (one plate slides beneath another) or continental collision. Example: Himalayas.
• Transform Boundaries: Plates slide horizontally past each other. Example: San Andreas Fault.

Transform Boundaries and Earthquakes

• Mechanism: At transform boundaries, the plates do not collide or pull apart; they grind past each other. This movement is not smooth. Friction between the plates causes them to stick.
• Stress Accumulation: As the plates try to move, immense stress builds up in the rocks along the fault line. This accumulated stress is stored as elastic strain energy.
• Sudden Release: When the stress exceeds the strength of the rocks or the friction holding them, the rocks suddenly break and slip, releasing the stored energy in the form of seismic waves. This rapid release of energy causes an earthquake.
• Earthquake Intensity: The magnitude and intensity of earthquakes at transform boundaries depend on the amount of stress released and the length and depth of the fault rupture. These boundaries are known for producing powerful and shallow earthquakes.

Key Examples

• The San Andreas Fault in California is a classic example of a transform boundary responsible for numerous earthquakes, some of which have been very destructive.
• The North Anatolian Fault in Turkey is another major transform fault system that experiences frequent and strong seismic activity.

Relevance to Exam Preparation

• Understanding the different types of plate boundaries is crucial for geography and geology-related competitive exams.
• The relationship between plate movement, stress accumulation, and earthquake generation at transform boundaries is a frequently tested concept.
• Knowing specific examples like the San Andreas Fault can help in answering questions related to real-world geological phenomena.