P12.7 Seismic waves Flashcards
What is seismology?
The study of earthquakes
When does an earthquake happen?
When forces inside the Earth increase and become strong enough to break and move layers of rock
What are seismic waves?
The energy transferred makes shock waves called seismic waves
How thick is the crust?
50Km
What is the focus?
Where the earthquakes originates from
What is the epicentre?
The nearest point on the surface to the focus - directly above the focus
What is the purpose of seismometres?
To record earthquakes
What are Primary waves (P-waves)?
These are longitudinal waves that push or pull on material as they move through the earth
Also cause initial tremors
What are Secondary waves (S-waves)?
They are transverse waves that ravel more slowly than P-waves
They shake the material that they pass through from side to side
What are L-waves?
These waves arrive last and cause violent movements on the surface up and down as well as backwards and forwards
Only happens in the Earth’s curst
Why do the waves bend at the mantle?
P-waves and S-waves bend as they travel through the mantle
This is because their speed changes due to the change in density throughout the mantle
Why do we P-waves refract at the boundary between the mantle and the outer core?
This is because their speed changes abruptly at the boundary
Why can’t S-waves travel through the liquid outer core?
Since they are transver waves
What is the shadow zone?
A zone from about 105 to 142 degrees where no P-waves or S-waves are recorded
Why does the existence of the shadow zone show that there is a liquid core under the mantle?
S-waves cant travel through the outer core because they are transverse waves and cannot travel through liquid
