Interior of the Earth
EXERCISES
1. Multiple choice questions.
(i) Which one of the following earthquake waves is more destructive?
(a) P-waves (c) Surface waves
(b) S-waves (d) None of the above
Ans: (c) Surface waves.
(ii) Which one of the following is a direct source of information about the interior of the earth?
(a) Earthquake waves (c) Gravitational force
(b) Volcanoes (d) Earth magnetism
Ans: (b) Volcanoes.
(iii) Which type of volcanic eruptions have caused Deccan Trap formations?
(a) Shield (c) Composite
(b) Flood (d) Caldera
Ans: (b) Flood.
(iv) Which one of the following describes the lithosphere:
(a) upper and lower mantle (c) crust and core
(b) crust and upper mantle (d) mantle and core
Ans: (b) crust and upper mantle
2. Answer the following questions in about 30 words.
(i) What are body waves?
Ans: Earth's inside shivers! Body waves travel through the planet itself, like ripples shaking a Jell-O. There are two types:
*P-waves: Push and pull like sound waves, zooming through any material.
*S-waves: Shake the ground sideways, needing solid rock to wiggle through.
These silent tremors reveal Earth's hidden layers and warn us of distant earthquakes. So next time you feel a rumble, remember, body waves are shaking the planet beneath your feet!
(ii) Name the direct sources of information about the interior of the earth.
Ans: Deep Earth! Mining, volcanic eruptions, and drilling projects crack Earth's shell, offering firsthand glimpses of what lies within. These direct sources tell tales of hidden rocks, scorching temperatures, and even ancient mysteries.
(iii) Why do earthquake waves develop shadow zone?
Ans: Liquid core plays tricks! P-waves bend, S-waves get blocked, creating a zone beyond 105° where Earth whispers no quake secrets to seismographs. It's like an Earthly cloak of silence around the hot, molten heart.
(iv) Briefly explain the indirect sources of information of the interior of the earth other than those of seismic activity.
Ans: Beyond the tremors, Earth whispers:
*Gravity: Uneven density across the planet reveals internal structures.
*Magnetic field: Its fluctuations hint at swirling currents deep within.
*Meteorites: Studying their composition gives clues about Earth's early materials.
*Temperature & Pressure: Increase with depth, offering hints about core conditions.
Through these whispers, we piece together the story of Earth's hidden layers, one clue at a time.
3. Answer the following questions in about 150 words.
(i) What are the effects of propagation of earthquake waves on the rock mass through which they travel?
Ans: When earthquake waves rip through the Earth's crust, they don't just pass silently. Their journey through the rock mass leaves a trail of effects, both subtle and dramatic:
Rock Deformation:
*Compression and Extension: P-waves push and pull rocks, causing temporary changes in shape.
*Shearing: S-waves shake rocks sideways, potentially causing permanent deformation and even fractures.
*Rock Bursts: Sudden releases of stored energy within rock masses, triggered by wave-induced stresses.
Ground Shaking:
*Vibrations: All types of waves cause the ground to tremble, with intensity depending on magnitude and distance.
*Amplification: Seismic waves can increase in intensity when encountering specific rock formations.
*Landslides and Liquefaction: Strong shaking can trigger landslides in unstable slopes and even liquefy loose, saturated soils.
Other Effects:
*Acoustic Emissions: Rocks emit faint sounds as they undergo stress and deformation.
*Changes in Groundwater Levels: Seismic waves can alter the flow of groundwater within the rock mass.
*Damage to Infrastructure: Ground shaking and rockfalls can damage buildings, bridges, and other structures.
These effects highlight the significant impact of earthquake waves on the rock mass. They remind us that earthquakes are not just tremors; they are powerful forces capable of reshaping landscapes and posing serious threats to life and infrastructure.
(ii) What do you understand by intrusive forms? Briefly describe various intrusive forms.
Answer By: Himashree Bora.