SSC Selection Post - Higher Secondary Level - 28th July 2025 - Shift 2

Correct Answer

Plate Tectonics

Explanation

Plate tectonics is the scientific theory that explains the large-scale motions of Earth's lithosphere (the crust and uppermost mantle). The Earth's outer shell is divided into several large and small rigid plates, known as tectonic plates. When these plates collide with each other (convergent), move away from each other (divergent), or slide parallel past each other (transform), heavy friction and stress build up along their edges. When this stress is suddenly released, energy is discharged in the form of seismic waves, which we experience as earthquakes.

The other terms listed in the options relate to geographical and geological processes but are not the direct cause of earthquakes. Erosion is the process by which natural forces like water, wind, or ice wear away and transport rocks and soil. Sedimentation is the process where small particles or sediment suspended in water or air settle down and accumulate. Convection is the process of circulation of hot fluids within the Earth's mantle; although convection currents are the engines responsible for driving the movement of tectonic plates, the movement of the plates themselves is called plate tectonics.

Key Points

The movement and interaction of tectonic plates are responsible for most of the world's earthquakes and volcanic eruptions. The boundaries between these plates are called fault lines, and most seismic activities occur near these boundaries. The Pacific Ring of Fire is the prime example of this, where 90% of the world's earthquakes occur due to highly active tectonic plate movements.

Additional Facts

Tectonic plate movements occur at three types of boundaries: convergent (when plates collide, such as the formation of the Himalayas), divergent (when plates pull apart, such as the Mid-Atlantic Ridge), and transform (when plates grind horizontally past each other, such as California's San Andreas Fault). Earthquakes occurring at transform boundaries like the San Andreas Fault are often highly destructive because the plates grind directly past each other without any vertical movement.

Important Questions and Answers

Question: Which scale is used to measure the intensity of an earthquake, and by which instrument is it recorded?

Answer: The intensity or magnitude of an earthquake is measured on the Richter Scale or the Mercalli Scale, and the instrument used to record it is called a seismograph or seismometer.

Question: What is the point within the Earth where seismic energy waves originate called?

Answer: The point within the Earth is called the focus or hypocenter, and the point directly above it on the Earth's surface is called the epicenter.