Earthquakes Lecture Practice Geography

Introduction to Earthquakes

• Definition: An earthquake is defined as an intense shaking of the Earth's surface. This phenomenon is caused by movements occurring in the Earth's outermost layer.

• Occurrence and Origin:

  • Earthquakes result from sudden movements along faults located within the Earth.

  • They are not limited to landmasses; they can occur both on land and in the sea.

  • A significant majority of earthquakes happen close to the Earth's surface.

• Location Recognition: The transcript mentions POWIIS (Prince of Wales Island International School) in Tanjung Bungah.

Causes and Tectonic Plate Interactions

• The Nature of Earth's Outer Layer: The Earth's outer layer consists of tectonic plates that are in constant motion.

• The Mechanism of Seismic Stress:

  • As tectonic plates interact at their respective boundaries, stress builds up over time.

  • When this accumulated stress is released suddenly, the rocks along faults either break or slip.

  • This sudden release of energy is what triggers an earthquake.

• Importance of Understanding: Knowledge of tectonic plates is essential for identifying high-risk areas and developing strategies to prepare for and reduce the impact of seismic events.

Measuring Earthquake Intensity: The Richter Scale

• Measurement Tools:

  • Seismograph / Seismometer: Instruments used to detect seismic waves generated by an earthquake. They measure the amplitude (height) of the waves to calculate the earthquake's magnitude.

  • Magnitude: This term refers to the specific strength of an earthquake.

• The Richter Scale: A logarithmic scale used to quantify the magnitude of an earthquake.

  • Logarithmic Scaling: Each whole number increase on the Richter scale represents an increase of approximately $10$ times in wave amplitude (size).

  • Energy Release: Each whole number increase on the scale corresponds to the release of approximately $31.6$ times more energy.

• Classification of Magnitudes and Effects:

  • Micro (Less than $2.0$): These are usually not felt by people.

  • Minor ($2.0$ to $3.9$): Often felt by some people but rarely causes any physical damage. Dishes may rattle.

  • Light ($4.0$ to $5.9$): Noticeable shaking of objects; windows shake and dishes rattle. May cause light damage.

  • Strong ($6.0$ to $6.9$): Can cause damage to buildings and other structures. Walls may crack, and some buildings may be damaged.

  • Major ($7.0$ to $7.9$): Causes serious damage to well-built structures. Heavy damage occurs to buildings, bridges, and roads.

  • Great ($8.0$ and above): Results in severe and very heavy damage to buildings, infrastructure, and the ground itself. Effects include ground cracking and landslides.

Key Structural Components: Focus and Epicentre

• Focus (Hypocentre): The point within the Earth where the earthquake rupture starts.

  • Deep-focus earthquakes: Earthquakes where the focus is located deep within the Earth's crust or mantle.

  • Shallow-focus earthquakes: Earthquakes that originate closer to the surface. These typically cause more significant damage because the seismic energy has less distance to travel and dissipate before reaching the surface.

• Epicentre: The point on the Earth's surface directly vertically above the focus.

• Seismic Waves: The energy waves that travel through the Earth's layers as a result of an earthquake.

• Fault: A fracture or zone of fractures between two blocks of rock, along which movement has occurred.

Tectonic Plate Boundary Types

• Constructive (Divergent) Plate Boundary:

  • Movement: Plates move apart from one another.

  • Process: Magma rises from the mantle to fill the gap created by the separating plates, forming new crust.

  • Outcome: Causes volcanoes and earthquakes.

  • Examples: The Mid-Atlantic Ridge and Iceland.

• Destructive (Convergent) Plate Boundary:

  • Movement: Plates move towards each other.

  • Process: One plate (often the thinner oceanic plate) may go under another (continental plate) and be destroyed as it melts back into the mantle.

  • Outcome: Causes volcanoes (often) and earthquakes.

  • Examples: The Andes Mountains and Japan.

• Conservative (Transform) Plate Boundary:

  • Movement: Plates slide past each other horizontally.

  • Process: No new crust is created and no crust is destroyed. However, the friction between the grinding plates causes intense stress.

  • Outcome: Causes earthquakes.

  • Examples: The San Andreas Fault in California.

Questions & Discussion

• Starter Activity Questions:

  1. Have you ever felt an earthquake? What did it look or feel like?

  2. Why do you think earthquakes happen?

  3. Which parts of the world do you think experience the most earthquakes?

• Activity 1: Understanding the Basics:

  1. Define 'earthquake' in your own words.

  2. What causes an earthquake?

  3. Where can earthquakes occur?

  4. Why do most earthquakes happen close to the Earth's surface?

  5. How are earthquakes linked to tectonic plates?

  6. Why is it important to understand where earthquakes happen?

• Activity 4: Focus VS Epicentre (Comparison Table):

  • The student is required to define 'Focus (Hypocentre)' and 'Epicentre', identify their locations, explain how they relate to each other, and identify where the strongest shaking usually occurs.

• Activity 5: Richter Scale Challenge:

  1. If an earthquake has a magnitude of $6.5$, how would you describe its strength and possible effects? (Context: Strong/Wall cracks/Building damage).

  2. How much more energy is released by a magnitude $7.0$ earthquake compared to a magnitude $6.0$ earthquake? (Context: Approximately $31.6$ times).

  3. Why is it important for scientists to measure the magnitude of an earthquake?

• Activity 6: Real-World Scenario:

  • The task involves advising a coastal city near a convergent plate boundary. The report must explain why the city experiences earthquakes, identify hazards (earthquakes, tsunamis, landslides), and suggest three mitigation actions.

• Extension Challenge (Fact File):

  • Research a recent major earthquake (within the last $10$ years) including: location and tectonic plate boundary, magnitude on the Richter Scale, depth of focus, effects on people and environment, and the response/preparation measures taken.

Homework and Administration

• Due Date: Activity $7$ is due on Tuesday next week, May $19$.