Willer Academy

Nation Builders Through Education | Founded by Er. Rahul Kumar Dubey Sir

Chapter 9: Earthquakes and Tsunamis

Subject: Science (Geography/Physics)

Class: 7

Series: Base Builder for Moderate to Hard

Learning Objectives

By the end of this chapter, you, the future scientist and nation-builder, will be able to:

1. Understand the causes of earthquakes and how they occur
2. Explain the relationship between tectonic plates and seismic activity
3. Differentiate between earthquake magnitude and intensity
4. Understand how tsunamis are generated and their characteristics
5. Explain safety measures during earthquakes and tsunamis
6. Interpret seismic data and understand the Richter scale
7. Apply knowledge to real-life seismic situations

9.1 Introduction: The Restless Earth

Earthquakes and tsunamis are powerful natural phenomena that result from the movement of Earth's tectonic plates. Understanding these forces helps us predict seismic events and prepare for potential disasters.

Quick Check

Have you ever experienced an earthquake or know someone who has? What was it like? How did people react?

9.2 Tectonic Plates and Earth's Structure

The Earth's crust is made up of large pieces called tectonic plates that float on the semi-fluid mantle below. These plates are constantly moving, interacting, and causing seismic activity.

Earth's Layers

• Crust: 5-70 km thick, solid rock
• Mantle: 2900 km thick, semi-solid rock
• Outer Core: Liquid iron and nickel
• Inner Core: Solid iron and nickel

Plate Boundaries

• Divergent: Plates moving apart
• Convergent: Plates colliding
• Transform: Plates sliding past each other
• Subduction: One plate going under another

Eurasian Plate

Pacific Plate

North American Plate

African Plate

Numerical & Application 1: Plate Movement

• Scenario: The Pacific Plate moves northwest at a rate of about 7 cm per year relative to the North American Plate.
• Problem: How far will the plate move in 100 years? In 1 million years? (Convert to kilometers)
• Solution:
  • 100 years: 7 cm/year × 100 years = 700 cm = 7 m
  • 1 million years: 7 cm/year × 1,000,000 years = 7,000,000 cm = 70 km

This shows how small annual movements create massive changes over geological time!

Experiment: Simulating Plate Boundaries

Take two pieces of thick paper or cardboard. Push them together to simulate convergent boundaries (mountains form). Pull them apart for divergent boundaries (rifts form). Slide them past each other for transform boundaries (friction and sudden release). Observe how these movements create different geological features.

9.3 Earthquakes: Causes and Measurement

Earthquakes occur when energy stored in Earth's crust is suddenly released, generating seismic waves that shake the ground.

Earthquake Features

• Focus: The point where the earthquake originates
• Epicenter: The point directly above the focus on the surface
• Seismic Waves: P-waves, S-waves, and Surface waves
• Faults: Fractures where movement occurs

Measuring Earthquakes

• Richter Scale: Measures energy released (magnitude)
• Mercalli Scale: Measures effects and damage (intensity)
• Seismograph: Instrument that records seismic waves

1-3

Minor

Usually not felt

Microearthquakes

4-5

Light

Felt, minor damage

6,200 per year

6-7

Strong

Destructive in populated areas

100 per year

8+

Great

Serious damage over large areas

1 per year

Task 1: Earthquake Research

Research a major earthquake that occurred in your country or region. Document its magnitude, effects, and the safety measures people took. Present your findings in a brief report.

9.4 Tsunamis: Formation and Characteristics

Tsunamis are series of enormous waves created by an underwater disturbance such as an earthquake, volcanic eruption, or landslide.

Tsunami Formation

1. Undersea earthquake displaces water column

2. Energy propagates outward as waves

3. Waves travel at high speed in deep ocean

4. Waves slow down and amplify near shore

5. Massive waves inundate coastal areas

Numerical & Application 2: Tsunami Speed

• Scenario: Tsunami wave speed in the open ocean can be calculated using the formula: v = √(g×d) where g is gravity (9.8 m/s²) and d is ocean depth.
• Problem: Calculate the speed of a tsunami in the Pacific Ocean where the average depth is 4280 m. How long would it take to travel 5000 km?
• Solution:
  • v = √(9.8 × 4280) = √(41944) ≈ 205 m/s or 740 km/h
  • Time = Distance/Speed = 5000 km / 740 km/h ≈ 6.76 hours

This shows why tsunamis can cross entire oceans in less than a day!

9.5 Safety Measures During Earthquakes and Tsunamis

Knowing how to stay safe during seismic events is crucial for protection and survival.

Earthquake Safety Precautions

Before

Secure heavy furniture, prepare emergency kit, identify safe spots

During

Drop, Cover, and Hold On; stay away from windows

After

Check for injuries, be cautious of aftershocks, avoid damaged buildings

Tsunami Safety Precautions

Warning Signs

Strong earthquake, unusual ocean behavior, rapid water retreat

Evacuation

Move to high ground immediately, follow official evacuation routes

After

Wait for official all-clear, be cautious of flooding and debris

Task 2: Emergency Plan

Create an emergency plan for your family in case of an earthquake or tsunami. Include meeting points, emergency contacts, and evacuation routes. Practice the plan with your family members.

Section C: Answer in Detail (For Answer Writing Practice)

Q1. Explain how earthquakes occur. What is the relationship between tectonic plates and seismic activity?

Hint: Discuss plate boundaries, fault lines, and energy release.

Q2. Describe how a tsunami forms and travels across the ocean. Why do tsunami waves become much higher as they approach the shore?

Hint: Include wave energy, water depth, and coastal topography.

Q3. What safety measures should be taken during and after an earthquake? Create a detailed emergency preparedness plan.

Hint: Include before, during, and after earthquake precautions.

Section D: Tackle These! (Higher Order Thinking Skills - HOTS)

Q1. Why are some regions more prone to earthquakes than others? Explain the concept of the "Ring of Fire" and its significance in seismic activity.

Think about: Plate boundaries, volcanic activity, and historical earthquake patterns.

Q2. How might climate change affect the frequency and intensity of earthquakes and tsunamis in the future? What scientific evidence supports your prediction?

Think about: Melting glaciers, sea level rise, and isostatic rebound.

Q3. Design an early warning system for tsunamis in a coastal community. What components would you include and how would you ensure all residents receive timely warnings?

Think about: Technology, communication methods, and community education.

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"The Earth has its own language, and through earthquakes and tsunamis, it reminds us of its immense power." - Keep learning, keep growing.

Er. Rahul Kumar Dubey Sir

Willer Academy - Building a Stronger Nation, One Student at a Time.