Earthquake theory

Question 1

Where are earthquakes distributed globally?

Answer 1

Along plate boundaries (destructive, constructive, conservative, and collision).

The Ring of Fire (Pacific Ocean) is the most active seismic region.

Intra-plate earthquakes can occur due to reactivation of ancient faults.

Question 2

What is an earthquake?

Answer 2

An earthquake is the sudden release of energy in the Earth’s crust, causing seismic waves. This usually happens when stress along a fault exceeds the rock’s strength.

Question 3

How is an earthquake generated?

Answer 3

Stress builds up at plate boundaries due to tectonic movements.

When the stress exceeds the strength of the rocks, they fracture along a fault.

This releases energy as seismic waves.

Question 4

What are the epicentre and focus of an earthquake?

Answer 4

Focus: The point inside the Earth where the earthquake starts.

Epicentre: The point on the Earth’s surface directly above the focus.

Question 5

Primary (P) waves:

Answer 5

Fastest, travel through solids and liquids.

Longitudinal waves (compression and expansion).

Question 6

Secondary (S) waves:

Answer 6

Slower, travel only through solids.

Transverse waves (up and down motion).

Question 7

Surface waves:

Answer 7

Slowest but most damaging.

Travel along the Earth’s surface.

Question 8

How are earthquakes categorized by depth?

Answer 8

Shallow-focus: 0-70 km deep; most destructive.

Intermediate-focus: 70-300 km deep.

Deep-focus: 300-700 km deep; less destructive.

Question 9

How are the magnitude and intensity of earthquakes measured?

Answer 9

Magnitude: Measures energy released, using the Richter Scale (logarithmic).

Intensity: Measures the impact and damage, using the Modified Mercalli Scale (I to XII)