Seismic waves

Question 1

What are the 4 parts of Earth?

Answer 1

• inner core
• outer core
• mantle
• crust

Question 2

What is the inner core?

Answer 2

The inner core is very hot and contains dense solid iron.

Question 3

What is the outer core?

Answer 3

The outer core is very hot, is liquid and mostly contains iron.

Question 4

What is the mantle?

Answer 4

The mantle is hot, less dense and a mixture of solid and molten rock.

Question 5

What is the crust?

Answer 5

The crust is a very thin layer of solid rock.

Question 6

What does the crust float on?

Answer 6

The crust floats on a hot liquid called magma.

Question 7

What happens to magma when it comes to the surface?

Answer 7

When magma comes to the surface from erupting volcanoes, it is known as lava.

Question 8

What is the Earth’s crust split into?

Answer 8

The Earth’s crust is split into sections known as tectonic plates.

Question 9

What are tectonic plates?

Answer 9

Tectonic plates are what the Earth’s crust is split into. They move very slowly due to convection currents in the magma.

Question 10

What do sudden movements of tectonic plates cause?

Answer 10

Sudden movement of tectonic plates cause the shaking of the ground called earthquakes.

Question 11

How do seismic waves form?

Answer 11

• As two plates try to slide past one another, friction between them at first prevents them from moving.
• Eventually, the frictional forces cannot keep the plates still and they suddenly slip.
• The immense energy stored in the compressed plates is released in the form of seismic waves.

Question 12

Who first suggested the idea of the movements in the Earth’s crust in 1915?

Answer 12

Alfred Wegener.

Question 13

What is the evidence that supports the ideas of the movements in the Earth’s crust?

Answer 13

• ancient rocks round in East Africa are identical to those found in South America.
• fossils found in both regions were from the same species of ancient aquatic reptile.

Question 14

What are the three types of waves?

Answer 14

• P waves
• S waves
• L waves

Question 15

What features do P waves have?

Answer 15

• longitudinal
• speed: fast
• travel in solids: yes
• travel in liquids:yes

Question 16

What features do S waves have?

Answer 16

• transverse
• speed: slow
• travel in solids: yes
• travel in liquids: no

Question 17

What features do L waves have?

Answer 17

• combination
• speed: very slow
• travel in solids: yes
• travel in liquids: yes

Question 18

Why are earthquakes and tsunamis unpredictable?

Answer 18

• scientists cannot measure the pressure between tectonic plates
• the fault lines are often deep within the Earth’s crust

Question 19

How do scientists make predictions on the risk of earthquakes happening?

Answer 19

Scientists make predictions on the risk of earthquakes happening in a specific area, based on its earthquake history.

Question 20

What are seismic waves monitored with?

Answer 20

Seismic waves are monitored around the world using seismometers. The trace from a seismometer is called a seismograph.

Question 21

How can the distance from the seismometer to the epicentre of the earthquake be calculated?

Answer 21

The distance from the seismometer to the epicentre of the earthquake can be calculated from the time delay between receiving the P and S waves and their speeds.

Question 22

What can and can’t transverse S waves travel through?

Answer 22

Transverse S waves cannot travel through the liquid outer core of the Earth, but they can travel in solid crust and semi-solid mantle.

Question 23

What can and can’t longitudinal P waves travel through?

Answer 23

Longitudinal P waves can travel through all the different layers of the Earth, but as differing speeds, so they refract at the boundaries.

Question 24

What do both P and S waves travel through faster?

Answer 24

Both P and S waves travel faster in more dense materials, so the deeper inside the Earth - where there is very high pressure - the more dense the material and the faster both waves travel. This causes the waves to refract and follow curved paths.

Question 25

What do both P and S waves reflect?

Answer 25

Both P and S waves will reflect at the boundaries between the layers.

Question 26

What is the epicentre?

Answer 26

The epicentre is the point on the earth directly above the focus of an earthquake.

Question 27

Which wave would reach a seismometer first?

Answer 27

P waves.

Question 28

What happens to waves as they reach the boundaries of rock types?

Answer 28

Waves are both reflected and refracted at boundaries of rock types.