Seismic waves Flashcards
What are the 4 parts of Earth?
- inner core
- outer core
- mantle
- crust
What is the inner core?
The inner core is very hot and contains dense solid iron.
What is the outer core?
The outer core is very hot, is liquid and mostly contains iron.
What is the mantle?
The mantle is hot, less dense and a mixture of solid and molten rock.
What is the crust?
The crust is a very thin layer of solid rock.
What does the crust float on?
The crust floats on a hot liquid called magma.
What happens to magma when it comes to the surface?
When magma comes to the surface from erupting volcanoes, it is known as lava.
What is the Earth’s crust split into?
The Earth’s crust is split into sections known as tectonic plates.
What are tectonic plates?
Tectonic plates are what the Earth’s crust is split into. They move very slowly due to convection currents in the magma.
What do sudden movements of tectonic plates cause?
Sudden movement of tectonic plates cause the shaking of the ground called earthquakes.
How do seismic waves form?
- 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.
Who first suggested the idea of the movements in the Earth’s crust in 1915?
Alfred Wegener.
What is the evidence that supports the ideas of the movements in the Earth’s crust?
- 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.
What are the three types of waves?
- P waves
- S waves
- L waves
What features do P waves have?
- longitudinal
- speed: fast
- travel in solids: yes
- travel in liquids:yes
What features do S waves have?
- transverse
- speed: slow
- travel in solids: yes
- travel in liquids: no
What features do L waves have?
- combination
- speed: very slow
- travel in solids: yes
- travel in liquids: yes
Why are earthquakes and tsunamis unpredictable?
- scientists cannot measure the pressure between tectonic plates
- the fault lines are often deep within the Earth’s crust
How do scientists make predictions on the risk of earthquakes happening?
Scientists make predictions on the risk of earthquakes happening in a specific area, based on its earthquake history.
What are seismic waves monitored with?
Seismic waves are monitored around the world using seismometers. The trace from a seismometer is called a seismograph.
How can the distance from the seismometer to the epicentre of the earthquake be calculated?
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.
What can and can’t transverse S waves travel through?
Transverse S waves cannot travel through the liquid outer core of the Earth, but they can travel in solid crust and semi-solid mantle.
What can and can’t longitudinal P waves travel through?
Longitudinal P waves can travel through all the different layers of the Earth, but as differing speeds, so they refract at the boundaries.
What do both P and S waves travel through faster?
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.
