The question asks to identify the type of plate boundary associated with the maximum number of earthquakes. To answer this, we need to understand the characteristics of each type of plate boundary (convergent, divergent, and transform) and how they generate seismic activity.
A) Convergent boundary — Convergent boundaries, particularly subduction zones, are associated with the most intense tectonic activity, leading to both frequent and the most powerful earthquakes, including deep-focus earthquakes. The collision and subduction processes generate immense stress and friction, causing a high number of seismic events.
The question asks for the primary cause of earthquakes in the Himalayan region. This requires knowledge of plate tectonics, specifically the geological processes occurring in the Himalayan mountain range.
B) Collision between the Indian and Eurasian plates — This is the fundamental geological process responsible for the formation of the Himalayas and the high seismic activity in the region. The northward movement of the Indian plate and its collision with the Eurasian plate generates immense stress, leading to frequent and powerful earthquakes.
The question asks to identify the cause of "Reservoir-induced seismicity". This phenomenon refers to earthquakes triggered by human activities related to large water bodies. We need to evaluate each option to determine which one directly leads to such seismic events.
Correct Option: B) Filling of large dams with water
Reservoir-induced seismicity is a well-documented phenomenon where the filling of large reservoirs behind dams leads to an increase in seismic activity. The primary mechanisms involve the increased load on the Earth's crust due to the water's weight and, more importantly, the increase in pore pressure within the rock fractures beneath the reservoir. This increased pore pressure reduces the effective normal stress on existing faults, making them more likely to slip and generate earthquakes.
The question asks to identify the type of earthquake exemplified by the 1967 Koyna earthquake. This requires knowledge of different earthquake types and specific historical seismic events in India.
Correct Option: C) Reservoir-induced earthquake. The Koyna earthquake of 1967 is a classic and well-studied example of seismicity induced by the impoundment of water in a large reservoir.
The question asks to identify the fastest seismic wave among the given options. Seismic waves are vibrations generated by earthquakes or explosions, which travel through the Earth's interior and along its surface. They are broadly classified into body waves (P-waves and S-waves) and surface waves (Love waves and Rayleigh waves).
B) P-waves (Primary waves) — P-waves are compressional body waves that travel through solids, liquids, and gases. They are the fastest seismic waves, arriving first at seismograph stations.
This question tests knowledge about the properties of different types of seismic waves, specifically their ability to propagate through various states of matter (solids, liquids, gases). Understanding the nature of P-waves and S-waves is key to answering this question.
B) S-waves — S-waves are shear waves that require a solid medium to propagate because they depend on the shear strength of the material. Liquids and gases lack shear strength, so S-waves cannot pass through them. This property is crucial for understanding the Earth's interior, as the absence of S-waves in certain regions indicates the presence of liquid layers (like the outer core).