Global Explorers: Our Changing World · 6th Class · The Dynamic Earth · Autumn Term

Earthquakes: Shaking the Ground

Examine the causes and effects of earthquakes, including seismic waves and measurement scales.

• NCCA Curriculum Specifications
• NCCA: Primary - Natural Environments
• NCCA: Primary - The Earth and the Universe

About This Topic

Earthquakes result from sudden releases of energy along faults in the Earth's crust, often at tectonic plate boundaries. Students study seismic waves: primary P-waves that compress and expand materials while traveling fastest, secondary S-waves that shake side-to-side through solids only, and surface waves that roll along the ground causing widespread damage. They locate the focus as the rupture point underground and the epicenter directly above it on the surface.

This content supports NCCA Primary curriculum strands on natural environments and the Earth and universe. Students compare the Richter scale, which quantifies energy release through wave amplitude logged logarithmically, with the Mercalli intensity scale, which rates shaking effects on people and buildings from I to XII. Mapping convergent, divergent, and transform boundaries helps predict vulnerable zones, such as Japan or California.

Active learning suits this topic well. Students construct shake tables with varied building models or simulate waves with slinkies, turning invisible processes visible. These experiences build intuition for wave behavior and scale differences, while group predictions foster critical discussion and retention.

Key Questions

1. Analyze how seismic waves propagate through the Earth's crust.
2. Differentiate between the Richter scale and the Mercalli intensity scale.
3. Predict the areas most vulnerable to earthquake activity globally.

Learning Objectives

• Analyze the propagation patterns of primary, secondary, and surface seismic waves through Earth's layers.
• Compare and contrast the Richter and Mercalli scales for measuring earthquake magnitude and intensity.
• Identify global regions with high seismic activity based on tectonic plate boundaries.
• Explain the relationship between fault types and earthquake occurrence.
• Evaluate the impact of seismic waves on different types of structures.

Before You Start

Plate Tectonics: Moving Continents

Why: Understanding how tectonic plates interact is fundamental to explaining the causes of earthquakes and identifying vulnerable regions.

Layers of the Earth

Why: Knowledge of Earth's crust, mantle, and core is necessary to comprehend how seismic waves travel through different materials.

Key Vocabulary

Seismic Waves	Vibrations that travel through Earth carrying the energy released during an earthquake. They include P-waves, S-waves, and surface waves.
Focus	The point within the Earth where an earthquake rupture starts. This is the origin of the seismic waves.
Epicenter	The point on the Earth's surface directly above the focus of an earthquake. It is where the strongest shaking is often felt.
Richter Scale	A logarithmic scale that measures the magnitude of an earthquake based on the amplitude of seismic waves recorded by seismographs.
Mercalli Intensity Scale	A scale that measures the intensity of an earthquake based on observable effects, such as damage to buildings and how people perceive the shaking, using Roman numerals I to XII.

Watch Out for These Misconceptions

Common Misconception

Earthquakes only occur at volcanoes.

What to Teach Instead

Most stem from tectonic plate movements along faults, not magma. Push-pull plate models in groups let students feel stress build-up and sudden slips, clarifying separation from volcanic activity through shared observations.

Common Misconception

The Richter scale measures damage to buildings.

What to Teach Instead

Richter gauges total energy via wave size; Mercalli assesses local effects. Shake table tests with identical quakes but varied distances reveal intensity gradients, helping students distinguish scales via hands-on evidence.

Common Misconception

All seismic waves travel at the same speed.

What to Teach Instead

P-waves outpace S-waves, with surfaces slowest. Slinky relays timed by peers demonstrate speed differences directly, as students physically experience and measure propagation for accurate mental models.

Active Learning Ideas

Shake Table Simulation: Building Stability

Fill trays with jelly or sand and place toothpick structures of varying heights. Students gently shake trays to mimic P-, S-, and surface waves, noting which buildings withstand shaking best. Groups sketch results and explain wave impacts.

35 min·Small Groups

Slinky Wave Relay: Wave Types

Divide class into lines; assign roles for P-waves (quick pushes), S-waves (side wiggles), and surface waves (slow rolls). Each line demonstrates propagation speed and motion using slinkies. Class times waves and compares to real data.

25 min·Whole Class

Scale Sorting Cards: Richter vs Mercalli

Prepare cards with magnitude readings or damage descriptions. Pairs sort cards into Richter or Mercalli piles, then justify choices using criteria sheets. Discuss as a class with real earthquake examples.

30 min·Pairs

Global Risk Mapping: Plate Boundaries

Provide world maps and colored pencils. Small groups outline plate boundaries, shade high-risk zones, and label recent quakes. Present findings, predicting future hotspots based on patterns.

40 min·Small Groups

Real-World Connections

• Structural engineers in earthquake-prone cities like Tokyo and San Francisco design buildings using base isolation or damping systems to withstand seismic forces, drawing on knowledge of wave propagation and intensity scales.
• Seismologists at the United States Geological Survey (USGS) monitor seismic activity globally, analyzing data from seismometers to pinpoint earthquake locations, determine magnitudes, and issue alerts to communities.
• Emergency responders in regions affected by earthquakes, such as following the 2011 Tohoku earthquake in Japan, use intensity maps based on the Mercalli scale to prioritize rescue efforts and assess damage to infrastructure.

Assessment Ideas

Exit Ticket

Provide students with a scenario describing an earthquake's effects (e.g., 'Buildings swayed violently, windows shattered, and people ran outside'). Ask them to assign a Mercalli intensity level (I-XII) and justify their choice. Also, ask them to identify the epicenter's likely location relative to the observation point.

Quick Check

Show students diagrams illustrating P-waves, S-waves, and surface waves. Ask them to label each wave type and write one key characteristic for each (e.g., speed, direction of motion, medium it travels through).

Discussion Prompt

Pose the question: 'Why is it important to have both the Richter scale and the Mercalli scale for understanding earthquakes?' Facilitate a class discussion where students compare what each scale measures and its practical application for scientists and the public.

Frequently Asked Questions

What causes earthquakes?

Earthquakes occur when rocks along faults in the Earth's crust suddenly slip due to tectonic plate movements. Stress builds over time from plates pushing, pulling, or sliding past each other, then releases as seismic waves. This process happens mainly at plate boundaries but can occur elsewhere through induced stresses, linking to broader Earth dynamics students map in class.

How do the Richter and Mercalli scales differ?

The Richter scale measures an earthquake's magnitude, or total energy released, using logarithmic wave amplitude data from seismographs; a 7.0 quake releases 31 times more energy than a 6.0. The Mercalli scale rates intensity based on observed effects like shaking felt or structural damage, varying by location. Students practice with sorting activities to internalize these distinctions.

How can active learning help students understand earthquakes?

Active approaches like building shake tables or using slinkies for waves make abstract concepts tangible. Students experiment with variables such as building design or wave types, observe real-time effects, and collaborate on predictions. This builds deeper comprehension and retention compared to lectures, as direct manipulation reveals wave propagation and scale nuances through trial and error.

Which areas are most vulnerable to earthquakes?

Regions along tectonic plate boundaries face highest risk, including the Pacific Ring of Fire encircling the ocean with subduction zones like Japan and Chile. Transform faults like California's San Andreas also trigger frequent quakes. Mapping exercises help students identify patterns from convergent, divergent, and transform interactions, using recent data for global awareness.