Glossary with Definitions:
Term | Definition |
Natural Phenomenon | An event occurring in nature not caused by human beings, like earthquakes, cyclones, and volcanoes. |
Meteorological Phenomenon | Natural events related to weather, such as thunderstorms, lightning, and cyclones. |
Geological Phenomenon | Natural events related to the earth’s structure, like earthquakes and volcanic eruptions. |
Earthquake | A sudden shaking of the Earth’s surface caused by the movement of tectonic plates beneath the earth. |
Tectonic Plates | Large, rigid slabs of the Earth’s crust that move slowly over the mantle. |
Focus (of Earthquake) | The point inside the Earth where an earthquake originates. |
Epicenter | The point on the Earth’s surface directly above the earthquake’s focus. |
Seismic Waves | Shock waves that spread outward from the earthquake’s focus, causing the ground to shake. |
Tsunami | A series of huge sea waves caused mainly by underwater earthquakes, moving very fast and growing tall near shores. |
Aftershocks | Smaller earthquakes that follow the main shock of a major earthquake. |
Foreshocks | Small earthquakes that occur before a major earthquake, in the same area. |
Seismometer | An instrument that detects and records the strength and duration of earthquakes. |
Richter Scale | A logarithmic scale used to measure the magnitude (energy release) of earthquakes. |
Magnitude | A measure of the amount of energy released during an earthquake. |
Seismic Zone | Areas where earthquakes are more likely to occur due to active tectonic plates. |
Disaster Management Supplies | Emergency supplies like flashlights, first aid kits, and communication tools prepared to deal with disasters. |
Lithosphere | The rigid outer layer of the Earth, including the crust and the upper part of the mantle. |
Molten Magma | Hot, molten rock beneath the Earth’s surface that causes movement of tectonic plates. |
Structural Safety | The design and construction of buildings to withstand earthquakes and reduce damage. |
Something To Know
A. Fill in the blanks.
- ________ are the smaller earthquakes that happen in the same place before the main quake follows.
Answer – Foreshocks
- The ‘high wall sea waves’, caused by underwater earthquakes, are called ________.
Answer – Tsunami
- Earthquake is caused by a disturbance deep inside the ________ of earth.
Answer – Lithosphere
- The waves, associated with the tremors caused by earthquakes, are known as ________ waves.
Answer – Seismic
- Geologists, call the point of origin of earthquakes, as its ________.
Answer – Focus
- Destructive energy of an earthquake is measured on the ________ scale.
Answer – Richter
B. State True or False for the following statements.
- It is now possible to give exact predictions about the earthquakes.
Answer – False
- Earthquakes, beneath the ocean floor, can generate huge tidal waves.
Answer – True
- When the plates of the earth slide past each other, the energy released gives rise to waves known as seismic waves.
Answer – True
- Richter Scale is a simple linear scale.
Answer – False
- An earthquake, of magnitude 2.5 on Richter Scale, cannot be recorded on a seismometer.
Answer – False
- In highly seismic areas, it is better to have house made from mud or timber, than those made by using heavy construction materials.
Answer – True
C. Tick (✓) the correct option.
- The minor quake, that might occur before the main earthquake, is known as a—
major shock
main shock
aftershock
foreshock
Answer – foreshock
- A natural phenomenon, whose triggering is not associated with an earthquake, is—
tsunami
flood
landslide
eruption of volcano
Answer – flood
- Earthquakes occur when there is a sudden release of stored up energy in earth’s—
inner core
mantle
outer core
crust
Answer – crust
- The various layers of earth are marked as A, B, C and D as shown in the given figure.
The correct labelling, of these layers A, B, C and D of earth, is
- crust, B. outer core, C. mantle, D. inner core
- outer core, B. crust, C. mantle, D. inner core
- crust, B. mantle, C. outer core, D. inner core
- outer core, B. mantle, C. crust, D. inner core
Answer – A. crust, B. mantle, C. outer core, D. inner core ✅
Explanation:
Crust (A): The outermost, solid layer (thinnest part).
Mantle (B): The thickest layer, semi-solid, below the crust.
Outer Core (C): Liquid layer of molten iron and nickel.
Inner Core (D): Solid, extremely hot, and dense center.
- The epicenter of an earthquake is—
deep under the crust of earth.
on the surface of earth.
in the mantle of earth.
in the core of earth.
Answer – on the surface of earth
- The magnitudes of two earthquakes, A and B, on the Richter Scale, were 7 and 5, respectively. The strength of—
earthquake A is 100 times that of earthquake B.
earthquake A is 10 times that of earthquake B.
earthquake A is 2 times that of earthquake B.
earthquake A is 1/10 times that of earthquake B.
Answer – earthquake A is 100 times that of earthquake B.
D. Answer the following questions in brief:
- What is an earthquake?
Answer – An earthquake is a sudden shaking or trembling of the earth caused by the sudden release of energy stored in the earth’s crust.
- State any three of the ‘damaging effects’ of an earthquake.
Answer – Loss of human and animal lives.
Destruction of buildings, roads, and bridges.
Triggering of landslides, floods, and tsunamis.
- Explain the phenomenon of production of shock waves.
Answer – Use light-weight construction materials like wood and steel instead of heavy concrete.
Build flexible structures that can absorb seismic shocks.
Design houses with wide bases and low heights to provide stability.
Ensure proper foundation and use shock-absorbing materials.
Follow all seismic safety building codes and regulations.
- In the context of an earthquake, which of the two points: the focus or the epicenter, is deep under the ground?
Answer – (a) Inside the house:
Take shelter under a sturdy table or bed.
Stay away from windows, mirrors, and heavy furniture.
Do not use elevators; use stairs if evacuation is necessary.
(b) Outdoors:
Move to an open area away from buildings, trees, and electric poles.
Stay low to the ground and protect your head and neck.
Stay away from slopes that may trigger landslides.
- – Name the scale used for measuring the strength of an earthquake. Write the likely magnitude of (a) a mild earthquake (b) a highly destructive earthquake on this scale.
Answer – Build earthquake-resistant buildings.
Conduct regular earthquake drills and awareness programs.
Fix heavy furniture and appliances firmly to walls.
Keep emergency kits ready with food, water, medicines, and first-aid.
Follow government guidelines and seismic zone regulations strictly.
- An earthquake measures 3 on Richter Scale.
(a) Would it be recorded on the seismometer?
Answer – Yes, an earthquake measuring 3 on the Richter Scale would be recorded by a seismometer.
Explanation: According to the Richter Scale table provided in the text, earthquakes with a magnitude of 2.5 or higher are detectable by seismometers, even if they are not felt by people.
(b) Is it likely to cause much damage?
Answer – No, an earthquake of magnitude 3 on the Richter Scale is not likely to cause significant damage.
Explanation:
Earthquakes below 4.5 on the Richter Scale typically cause little to no damage.
Noticeable shaking may occur, but structural damage is rare.
Significant damage usually starts around magnitude 6.0 or higher.
E. Answer the following questions.
- Explain, in brief, the cause of an earthquake.
Answer – Earthquakes are caused by the sudden release of energy stored in the earth’s crust due to the movement of tectonic plates. When these plates collide, slide past, or move away from each other, stress builds up and eventually releases as seismic waves, causing the ground to shake.
- Where are the earthquakes more likely to occur?
Answer – Earthquakes are more likely to occur along the boundaries of tectonic plates, especially in seismic zones where two plates meet, such as the Himalayan region, the Pacific Ring of Fire, and other fault zones.
- Mr. Sarthak is the head of a construction company. He got a contract to design and build a housing complex in an area which was under the ‘seismic zone’. State the main precautions which Mr. Sarthak’s company should take so that houses, built by it, are durable.
Answer – Use light-weight construction materials like wood and steel instead of heavy concrete.
Build flexible structures that can absorb seismic shocks.
Design houses with wide bases and low heights to provide stability.
Ensure proper foundation and use shock-absorbing materials.
Follow all seismic safety building codes and regulations.
- State the precautions, that one should take for protection during an earthquake if one is (a) inside the house (b) outdoors.
Answer – (a) Inside the house:
Take shelter under a sturdy table or bed.
Stay away from windows, mirrors, and heavy furniture.
Do not use elevators; use stairs if evacuation is necessary.
(b) Outdoors:
Move to an open area away from buildings, trees, and electric poles.
Stay low to the ground and protect your head and neck.
Stay away from slopes that may trigger landslides.
- State the main precautions that can be taken to minimise the effect of an earthquake.
Answer – Build earthquake-resistant buildings.
Conduct regular earthquake drills and awareness programs.
Fix heavy furniture and appliances firmly to walls.
Keep emergency kits ready with food, water, medicines, and first-aid.
Follow government guidelines and seismic zone regulations strictly.
Value Based Questions
Rahul and Aakash are very good friends. When Rahul had fever a few weeks before the examination, Aakash decided to help him. He did not go for his badminton sessions and used this time to give Rahul all the help and information about the lessons taught in the school. Rahul’s mother observed this and remarked that the overall effect of Aakash’s timely help is, in a way, similar, but opposite, to the multiplicative effects of the magnitudes on the Richter Scale.
- State the values displayed by Aakash.
Answer – Aakash displayed the values of friendship, helpfulness, selflessness, compassion, and dedication.
- Name the quantity that is measured on the Richter Scale.
Answer – The Richter Scale measures the magnitude of an earthquake.
- By what factor does that quantity go up when its magnitude, on the Richter Scale, increases by one?
Answer – When the magnitude increases by one unit on the Richter Scale, the energy released increases by about 10 times.
Something To Do
- Visit an organisation which provides relief to those suffering from natural disasters. Discuss the role these organisations play in determining how cities/ regions prepare for, and react to, earthquakes. Prepare a brief report.
Answer – Relief organisations like the Red Cross, NDRF (National Disaster Response Force), and UNICEF play a major role in disaster management. They educate people about earthquake safety, conduct mock drills, create emergency kits, and help design earthquake-resistant buildings. After an earthquake, they provide medical aid, food, shelter, and emotional support. Their efforts make cities better prepared to face earthquakes and help reduce loss of life and property.
2- On the map of world, indicate the places where tsunami is more likely to occur. Try to find out the problems faced by people living in these regions. Take the help of newspaper clippings, school library or internet sources.
Answer – Tsunamis are more likely to occur along:
The Pacific Ring of Fire (Japan, Indonesia, Philippines, Alaska, Chile).
Coastal regions around the Indian Ocean (India’s eastern coast, Sri Lanka, Maldives).
Problems faced by people:
Loss of lives and property.
Flooding and contamination of drinking water.
Destruction of crops and food shortage.
Homelessness and displacement.
Spread of diseases after floods.
3- Take a slinky (2-3 m long). Tie its one end to the wall. Hold the other end firmly in your hand. Push and pull the slinky at the same time (for this you have to move your hand in a circle). Observe carefully. What happens to the slinky? This activity will give you an idea about the seismic (circular) waves.
[The surface/circular waves are the seismic waves which cause major destruction above the ground].
Answer – When the slinky is pushed and pulled in a circular motion, circular waves travel along the slinky. The motion of the slinky is similar to surface seismic waves which cause the ground to shake in all directions, leading to major destruction during earthquakes.
- Fill the crossword with suitable words on the basis of the clues given below.
Across
- sudden shaking of earth.
- weak areas on the earth where the earthquake is more likely to occur.
- used to record seismic waves.
- the place inside the earth’s crust from where the earthquake originates.
Down
- the point, on the earth’s surface, directly above the focus.
- a scale used to rate the strength of an earthquake.
- very large ocean waves.
- small quakes that may happen before the main quake.
Answer – Across:
sudden shaking of earth – Earthquake
weak areas on the earth where the earthquake is more likely to occur – Faults
used to record seismic waves – Seismograph
the place inside the earth’s crust from where the earthquake originates – Focus
Down:
the point, on the earth’s surface, directly above the focus – Epicenter
a scale used to rate the strength of an earthquake – Richter
very large ocean waves – Tsunami
small quakes that may happen before the main quake – Foreshocks
Additional Questions And Answers – 01
Short Answer Questions
- What is a fault in the earth’s crust?
Answer: A fault is a crack or fracture in the Earth’s crust where the blocks of land have moved relative to each other, causing earthquakes.
- Name two instruments used to detect and measure earthquakes.
Answer: Seismograph and Seismoscope.
- What are seismic waves?
Answer: Seismic waves are energy waves that are released during an earthquake and travel through the Earth.
- What is a seismograph?
Answer: A seismograph is an instrument that records the vibrations caused by seismic waves during an earthquake.
- What are aftershocks?
Answer: Aftershocks are smaller earthquakes that occur after the main earthquake as the crust adjusts to the changes.
Long Answer Questions
- Explain how the movement of tectonic plates causes earthquakes.
Answer: The Earth’s crust is divided into large plates called tectonic plates. These plates constantly move, but when they get stuck due to friction, stress builds up. When the stress exceeds the strength of rocks, it is suddenly released in the form of seismic waves, causing an earthquake.
- What safety measures should be taken before, during, and after an earthquake?
Answer: Before: Identify safe spots, keep emergency kits ready, strengthen the house structure.
During: Take shelter under a sturdy table, stay away from windows and heavy objects, do not use elevators.
After: Check for injuries, evacuate damaged buildings, stay tuned to emergency broadcasts, avoid open wires and gas leaks.
- What are the different types of seismic waves? Explain briefly.
Answer: P-waves (Primary waves): Fastest, travel through solids, liquids, and gases.
S-waves (Secondary waves): Slower, travel only through solids.
Surface waves: Move along the Earth’s surface and cause most of the damage.
MCQs (Multiple Choice Questions)
- Which of the following waves travels fastest during an earthquake?
- a) Surface waves
- b) S-waves
- c) P-waves
- d) None of these
Answer: c) P-waves
- The instrument used to measure the strength of an earthquake is—
- a) Barometer
- b) Thermometer
- c) Seismograph
- d) Altimeter
Answer: c) Seismograph
- What is the outermost layer of the Earth called?
- a) Core
- b) Crust
- c) Mantle
- d) Lithosphere
Answer: b) Crust
- Which scale measures the amount of damage caused by an earthquake?
- a) Celsius scale
- b) Richter scale
- c) Mercalli scale
- d) Kelvin scale
Answer: c) Mercalli scale
- Tsunamis are caused mainly by—
- a) Rainfall
- b) Hurricanes
- c) Underwater Earthquakes
- d) Volcanic ash
Answer: c) Underwater Earthquakes
True/False Statements
- S-waves can travel through liquids.
Answer: False
- Earthquake-prone zones are called seismic zones.
Answer: True
- During an earthquake, it is safe to run outside immediately.
Answer: False
- Most earthquakes are caused by the movement of tectonic plates.
Answer: True
- Richter Scale was developed by Charles F. Richter.
Answer: True
Additional Questions and Answers – 02
Fill in the Blanks:
- The point of origin of an earthquake inside the earth is called the ______.
Answer: focus
- The ______ scale measures the magnitude of an earthquake.
Answer: Richter
- Earthquakes under the ocean floor can cause destructive waves called ______.
Answer: tsunamis
- The outermost layer of the earth is called the ______.
Answer: crust
- Smaller earthquakes that occur before the main shock are called ______.
Answer: foreshocks
- The point on the earth’s surface directly above the focus is called the ______.
Answer: epicenter
- Earthquakes are caused by the movement of ______ plates.
Answer: tectonic
- A magnitude ______ earthquake or higher is considered destructive.
Answer: 6.0
Match the Columns:
Column A Column B
Focus (a) Point on the surface above the earthquake’s origin
Epicenter (b) Instrument recording earthquakes
Richter Scale (c) Origin point of an earthquake inside the earth
Seismometer (d) Scale measuring earthquake magnitude
Tsunami (e) Giant sea waves caused by underwater earthquakes
Answers:
1 – (c), 2 – (a), 3 – (d), 4 – (b), 5 – (e)
Assertion-Reason Questions:
Directions: Read the statements (Assertion and Reason) and choose the correct option:
- Both Assertion (A) and Reason (R) are true, and R is the correct explanation of A.
- Both A and R are true, but R is not the correct explanation of A.
- A is true, but R is false.
- A is false, but R is true.
- Assertion (A): Earthquakes cannot be predicted accurately.
Reason (R): They result from sudden movements of tectonic plates, which are unpredictable.
Answer: A (Both true, R explains A)
- Assertion (A): The inner core of the earth is liquid.
Reason (R): It is made of molten iron and nickel.
Answer: D (A is false; the inner core is solid due to extreme pressure)
- Assertion (A): A magnitude 5 earthquake is 100 times stronger than a magnitude 3.
Reason (R): The Richter Scale is logarithmic (each unit increase = 10× amplitude).
Answer: A (Both true; R explains A’s math: 10^(5-3) = 100×)
- Assertion (A): Tsunamis travel faster than cyclones.
Reason (R): Tsunamis can move at speeds up to 960 km/hr in deep water.
Answer: B (Both true, but R doesn’t directly compare tsunamis to cyclones)
- Assertion (A): Foreshocks always occur before major earthquakes.
Reason (R): Scientists use foreshocks to predict earthquakes reliably.
Answer: C (A is false—foreshocks are common but not guaranteed; R is also false as prediction is still unreliable)
Short Answer Questions:
- What is an earthquake?
Answer – An earthquake is a sudden tremor or movement of the earth’s crust, usually lasting for a very short time, originating naturally at or below the earth’s surface.
- What is the focus of an earthquake?
Answer – The focus is the point of origin of an earthquake deep inside the earth where tension is released.
- What is the epicenter?
Answer – The epicenter is the point on the earth’s surface directly above the focus.
- Name two effects of earthquakes.
Answer – Damage to buildings, bridges, and dams; loss of human life; floods and landslides.
- What causes a tsunami?
Answer – An earthquake occurring beneath the ocean floor can displace water, generating huge sea waves called tsunamis.
- What is the Richter scale used for?
Answer – It measures the magnitude (intensity) of an earthquake based on seismic wave amplitude.
- Why can’t earthquakes be predicted accurately?
Answer – Because they result from sudden movements of tectonic plates, and current technology cannot precisely determine when and where these movements will occur.
- What are foreshocks and aftershocks?
Answer – Foreshocks: Smaller earthquakes before the main shock.
Aftershocks: Smaller earthquakes following the main shock, lasting for weeks or months.
- What should you do if you are indoors during an earthquake?
Answer – Take shelter under a table, stay away from heavy objects, and protect your head.
- How do tectonic plates cause earthquakes?
Answer – Their slow movement builds up tension at plate boundaries, which, when released, causes seismic waves.
Long Answer Questions:
- Explain the causes and effects of earthquakes.
Answer – Causes: Earthquakes occur due to the movement of tectonic plates, volcanic eruptions, or meteor impacts. When plates slide past each other, friction causes tension to build up, which is suddenly released as seismic waves.
Effects: Destruction of buildings, loss of life, landslides, floods, and tsunamis.
- Describe the Richter scale and its significance.
Answer – The Richter scale measures earthquake magnitude logarithmically. Each increase of 1 means 10 times stronger shaking and ~32 times more energy release. For example, a magnitude 6 quake is 100 times stronger than a magnitude 4.
- What precautions should be taken before, during, and after an earthquake?
Answer – Before: Build earthquake-resistant structures, identify safe spots, and keep emergency supplies.
During: If indoors, hide under a table; if outdoors, stay in an open area.
After: Expect aftershocks, check for injuries, avoid damaged areas, and listen to official updates.
- How are tsunamis formed? Describe the 2004 Indian Ocean tsunami.
Answer – Tsunamis are caused by underwater earthquakes displacing water. The 2004 Indian Ocean tsunami (magnitude 9.1) killed over 230,000 people across 14 countries due to 30-meter-high waves.
- Why is earthquake prediction difficult? What methods are used to monitor them?
Answer – Prediction is hard because plate movements are unpredictable. Scientists use seismometers, study foreshocks, and observe animal behavior (e.g., agitated animals) as potential clues.
Multiple-Choice Questions (MCQs):
- What is the point inside the earth where an earthquake starts called?
- a) Epicenter
- b) Focus ✅
- c) Crust
- d) Richter point
- Which scale measures earthquake intensity?
- a) Celsius scale
- b) Richter scale ✅
- c) Beaufort scale
- d) Decibel scale
- What can earthquakes under the ocean cause?
- a) Cyclones
- b) Tornadoes
- c) Tsunamis ✅
- d) Thunderstorms
- Which of these is NOT an effect of earthquakes?
- a) Landslides
- b) Floods
- c) Volcanic eruptions ✅
- d) Building collapses
- What should you do during an earthquake if you are inside a building?
- a) Run outside
- b) Hide under a table ✅
- c) Stand near a window
- d) Use the elevator
True/False Questions:
- Earthquakes can be predicted with 100% accuracy. (False)
- The epicenter is the point on the surface directly above the focus. (True)
- A magnitude 7 earthquake is 10 times stronger than a magnitude 6. (False – it’s ~32 times stronger in energy)
- Tsunamis travel as fast as 960 km/hr. (True)
- Foreshocks always occur before major earthquakes. (False – they sometimes do, but not always)
Additional Activity-Based Question:
How can you model tsunami formation using a water-filled bowl?
Answer: Striking the table creates waves in the water, similar to how an underwater earthquake displaces ocean water, forming tsunamis.