All questions of Natural Hazards & Disasters for BPSC (Bihar) Exam

D.

The correct answer is option 'A': A is correct, and R is an appropriate explanation of A.

Explanation:
Observing the passage of earthquake waves through different layers of the Earth is a reliable method to understand the structure of the Earth. This is because different types of earthquake waves behave differently as they pass through various layers of the Earth.

- Earthquake Waves: Earthquake waves can be classified into two main types: body waves and surface waves. Body waves include primary waves (P-waves) and secondary waves (S-waves), while surface waves include Love waves and Rayleigh waves.

- Propagation of Earthquake Waves: P-waves are compressional waves that can travel through solids, liquids, and gases. They are the fastest seismic waves and can travel through all layers of the Earth, including the liquid outer core. S-waves, on the other hand, are shear waves and can only travel through solids. They cannot propagate through the liquid outer core and are only observed in the solid layers of the Earth.

- Explanation of Assertion and Reason: The assertion states that the structure of the Earth can be understood by observing the passage of earthquake waves through different layers. This is correct because the behavior of earthquake waves can provide valuable information about the composition and properties of the Earth's layers. The reason states that some type of earthquake waves do not travel through liquid material in Earth's layers. This is also correct because S-waves, which are a type of earthquake wave, cannot pass through the liquid outer core. Therefore, Reason is an appropriate explanation of Assertion.

In conclusion, by observing the behavior of earthquake waves, particularly the transmission and reflection of P-waves and S-waves, scientists can gather information about the different layers of the Earth. The passage of seismic waves through Earth's layers provides insights into the composition, density, and other physical properties of these layers.

The correct answer is option 'C' - 1 and 2 only. Let's understand each statement.

1. Body waves are generated due to the release of energy at the focus and move in all directions travelling through the body of the Earth.

- Body waves are seismic waves that travel through the interior of the Earth. They are generated due to the release of energy at the focus of an earthquake. There are two types of body waves: P waves (primary waves) and S waves (secondary waves).

- P waves are the fastest seismic waves and they travel through solids, liquids, and gases. They move in a push-pull or compressional motion, causing particles in the material to move back and forth in the direction of wave propagation. P waves can travel through both the Earth's mantle and core.

- S waves are slower than P waves and can only travel through solids. They move in a shearing or shaking motion, causing particles in the material to move perpendicular to the direction of wave propagation. S waves cannot travel through the Earth's outer core, which is liquid.

- Therefore, the first statement is correct as body waves are generated at the focus of an earthquake and they travel in all directions through the body of the Earth.

2. The body waves interact with the surface rocks and generate a new set of waves called surface waves.

- Surface waves are seismic waves that travel along the Earth's surface. They are generated when body waves interact with the surface rocks. Surface waves are slower than body waves but they cause more damage during an earthquake due to their larger amplitudes.

- There are two types of surface waves: Love waves and Rayleigh waves. Love waves move in a side-to-side motion, similar to the motion of a snake or a wave on the surface of water. Rayleigh waves move in an elliptical motion, causing particles in the material to move in a rolling motion.

- Therefore, the second statement is correct as body waves interact with surface rocks and generate surface waves.

3. The denser the material, the lower is the velocity of these waves.

- This statement is incorrect. The velocity of seismic waves depends on the properties of the material through which they travel, including its density, elasticity, and rigidity. In general, denser materials tend to have higher velocities for seismic waves.

- For example, P waves travel faster through solids compared to liquids and gases because solids are denser and have higher elasticity and rigidity. Similarly, S waves can only travel through solids because they require a certain level of density and rigidity to propagate.

- Therefore, the third statement is incorrect as the velocity of seismic waves is generally higher in denser materials.

In conclusion, only statements 1 and 2 are correct.

Assertion (A): Shallow-focus earthquakes occur along transform boundaries.
Reason (R): Transform faults are found where plates slide past one another.

The correct answer is option 'A' - A is correct, and R is an appropriate explanation of A.

Explanation:
- Shallow-Focus Earthquakes:
- Shallow-focus earthquakes are earthquakes that occur within the upper 70 kilometers of the Earth's surface.
- The focus refers to the location within the Earth where the seismic energy is released.
- Shallow-focus earthquakes are typically associated with tectonic plate boundaries.

- Transform Boundaries:
- Transform boundaries are areas where tectonic plates slide past one another horizontally.
- These boundaries are characterized by transform faults, which are large strike-slip faults that accommodate the horizontal movement of the plates.
- Transform boundaries are found along oceanic ridges, where they connect segments of spreading mid-ocean ridges, and on land where they form the boundaries between two plates.

- Relationship between Shallow-Focus Earthquakes and Transform Boundaries:
- Transform boundaries are associated with shallow-focus earthquakes because of the intense stress and friction generated by the sliding of the plates.
- As the plates slide past each other, they can become locked due to friction. When the stress along the fault exceeds the strength of the rocks, it is released in the form of an earthquake.
- The shallow-focus earthquakes along transform boundaries are often characterized by strong shaking and can cause significant damage in populated areas.

- Assertion and Reason:
- The assertion (A) states that shallow-focus earthquakes occur along transform boundaries, which is true.
- The reason (R) provides an appropriate explanation for this phenomenon by stating that transform faults are found where plates slide past one another.
- The sliding motion at transform boundaries generates stress and friction, leading to the occurrence of shallow-focus earthquakes.

- Conclusion:
- Based on the above explanation, it can be concluded that assertion (A) is correct, and reason (R) is an appropriate explanation of assertion (A).
- Therefore, the correct answer is option 'A'.

The what? Can you please provide more context or clarify your question?

Mid-Atlantic ridges, hot spots and plate boundaries are major sources for volcanoes.

Highly fluid ones are less viscous, hence are less explosive while the acidic ones arc explosive due to high viscosity.

Distribution of Volcanoes: Overview
The distribution of volcanoes on Earth is closely related to tectonic plate boundaries. Understanding the statements provided helps clarify volcanic activity in various regions.
Statement 1: Atlantic Coasts and Active Volcanoes
- The Atlantic Ocean is generally not known for a high concentration of active volcanoes.
- Most volcanic activity occurs along the Pacific Ring of Fire, not the Atlantic.
- The mid-Atlantic ridge does host some volcanic activity, but it's primarily undersea and not characterized by many active volcanoes on the coasts.
Statement 2: Pacific Ocean and Active Volcanoes
- The Pacific Ocean is home to the majority of the world’s active volcanoes, particularly along its coastlines.
- The Ring of Fire, which encircles the Pacific Ocean, is a major area for volcanic activity due to tectonic plate interactions, including subduction zones and fault lines.
- This region has a significant number of folded and faulted landforms, contributing to the high volcanic activity.
Conclusion
Given the above analysis, only Statement 2 is correct. The Pacific Ocean indeed has the highest number of active volcanoes due to its geological features, while Statement 1 incorrectly suggests a significant presence of active volcanoes along the Atlantic coasts.
Thus, the correct answer is option 'B': 2 only.

Seismic Waves

Seismic waves are vibrations that travel through the Earth's layers in response to an earthquake or other geological events. These waves carry energy and provide valuable information about the Earth's interior.

P Waves

P waves, also known as primary waves or compressional waves, are the fastest type of seismic waves. They are longitudinal waves that travel through both solids and liquids. P waves cause particles to move back and forth in the same direction as the wave is traveling. Due to their ability to propagate through liquids, P waves can travel through the Earth's core, which is predominantly liquid.

S Waves

S waves, also known as secondary waves or shear waves, are slower than P waves. They are transverse waves that cause particles to move perpendicular to the direction of wave propagation. S waves can only travel through solids and cannot propagate through liquids or gases. This is because liquids do not possess the necessary rigidity to support shear stresses.

Explanation of the Statements

(a) The statement "P wave or primary wave is the fastest kind of seismic wave and, consequently, the first to arrive at a seismic station" is correct. P waves have a higher velocity compared to S waves, allowing them to reach a seismic station before the arrival of S waves. The arrival time of P waves is used to determine the epicenter of an earthquake.

(b) The statement "S wave or secondary wave can only move through solid rock, not through any liquid medium" is also correct. S waves require a solid medium for propagation and cannot transmit through liquids. When an earthquake occurs, the absence of S waves at a seismic station indicates the presence of a liquid layer, such as the Earth's outer core.

Conclusion

In summary, both statements (a) and (b) are correct. P waves are the fastest seismic waves and arrive first at a seismic station, while S waves can only propagate through solid media and are unable to pass through liquids.

Sources of earthquakes

• Tectonic earthquakes - sliding of plates along a fault plane.
• Volcanic earthquakes - Collapse of roofs of underground mines.

Explanation:

Laccoliths and batholiths are both forms of intrusive igneous rock formations. However, the given descriptions of these formations are not accurate. Let's discuss each one separately:

Laccoliths:
- Laccoliths are formed when magma is injected into the crust and spreads out between existing rock layers.
- The magma pushes the overlying rock layers upward, creating a dome or mushroom-like shape.
- As the magma cools and solidifies, it forms a concordant intrusive body (meaning it follows the layering of the surrounding rocks).
- Laccoliths are typically smaller in size compared to batholiths.

Batholiths:
- Batholiths are also formed by the intrusion of magma into the crust, but they are much larger in size.
- They are characterized by their level base and lack of a pipe-like conduit.
- Batholiths represent a massive body of igneous rock that extends over a large area and is typically exposed at the surface due to erosion of the overlying rocks.
- They are also concordant intrusive bodies.

Understanding the given statements:
- The given statements incorrectly describe laccoliths as "large domes that cool in the deeper depth of the crust."
- Similarly, batholiths are inaccurately described as "large dome-shaped bodies with a pipe-like conduit from below."
- These descriptions do not match the actual definitions of laccoliths and batholiths, making the given statements incorrect.

Correct Answer:
- Based on the above explanation, the correct answer is option 'D' - None of the above, as both statements are inaccurate.

There are three types of plate boundaries: spreading zones, transform faults and subduction zones.