Seismic Shadow Zones and Earth Structure

The video explains the concept of seismic shadow zones, focusing on P and S waves. P waves refract at the core-mantle boundary, creating a shadow zone between 104° and 140°. S waves, traveling slower and in a shearing motion, are stopped by the liquid core, creating a broader shadow zone. These observations led to the discovery of the Earth's liquid outer core in the early 20th century.

What is a seismic shadow zone primarily used for in teaching?

• Predicting future earthquakes

• Understanding earthquake magnitudes

• Teaching Earth's structure

• Measuring seismic wave speed

How do P waves behave at the core-mantle boundary?

• They speed up and travel straight

• They reflect back to the surface

• They are absorbed completely

• They refract and slow down

What causes the shadow zone between 104 to 140 degrees from an earthquake?

• Refraction of P waves

• Reflection of P waves

• Absorption of S waves

• Diffraction of surface waves

Why do S waves create a broader shadow zone beyond 104 degrees?

• They travel faster than P waves

• They are absorbed by the mantle

• They reflect off the Earth's surface

• They are stopped by the liquid core

What was the significance of the lack of S-wave arrivals in 1910?

• It suggested a liquid outer core

• It proved the existence of tectonic plates

• It showed the Earth's surface is liquid

• It indicated a solid inner core

By 1913, what was refined to define the core-mantle boundary?

• Earthquake epicenter locations

• Surface wave patterns

• P-wave shadow zone

• S-wave velocity

What enabled seismologists to deduce the presence of a liquid outer core?

• The absorption of S waves

• The reflection of P waves

• The refraction of seismic energy

• The speed of surface waves