Earth's Internal Structure: Seismic Waves (2.2.3)

Question 1

Energy and Seismic Waves

Answer 1

• Measure energy in joules (1 J = 1 Nm).
• Seismic waves emanate out all directions from earthquake focus.
• Surface waves: analogous to water waves, travel along Earth’s surface.
• Body waves: travel through interior (faster than surface waves).
• P-wave (pressure wave)
• S-wave (shear wave)
• Rayleigh wave
• Love wave

Question 2

How is magnitude of earthquakes measured?

Answer 2

• Use Moment Magnitude Scale (not Richter Scale).
• Based on energy released (area of rupture x slip x rock rigidity).

Question 3

How often do large earthquakes occur?

Answer 3

• Only 7 large earthquakes (>8.8 magnitude) have occurred since 1900.
• 3 of them occurred past 15 years.

Question 4

How are historical earthquake sizes estimated?

Answer 4

• Moment Magnitude Scale and Richter Scale can’t be applied to any pre-WWII.
• Modified Mercalli Scale used (qualitative scale based on effects of earthquake from I to XII).

Question 5

What are the travel and arrival times of seismic waves?

Answer 5

• Body waves travel shorter distances than surface waves.
• Body waves faster than surface waves.
• P-, S-waves arrive first, followed by Love, Rayleigh waves.
• Difference in arrival times of P- and S-waves = locate epicentre of earthquake.