8 - Locating and measuring earthquakes

Question 1

what are P waves

Answer 1

are the primary waves and are compressional (like a slinky)

Question 2

what are S waves

Answer 2

are secondary waves and are shear waves (up and down)

Question 3

what are surface waves

Answer 3

• love or Rayleigh waves
• travel across Earth and take longer as have further to travel

Question 4

which seismic wave can’t mass through the earths core (liquid)

Answer 4

S waves

Question 5

how is seismic energy recorded

Answer 5

seismometers used by converting vibrations due to seismic waves into electrical signals which can then be analysed

Question 6

which seismic wave moves fastest

Answer 6

P waves faster than S waves - time difference between the two increases with distances

Question 7

how can epicentre be located

Answer 7

time difference of P and S waves to a seismic station can be used to determine the location

Question 8

what is local magnitude

Answer 8

• i.e. richter scale
• based on the amplitudes of seismic waves (log scale)
• invalid for larger magnitude earthquakes

Question 9

what is surface wave magnitude

Answer 9

• used to measure the surface waves of shallow earthquakes
• won’t work on deep earthquakes as these don’t cause surface waves

Question 10

what Is moment magnitude

Answer 10

more effective for larger earthquakes

Question 11

what is body wave magnitude

Answer 11

• used to measure earthquakes that are over 50km deep

Question 12

what is seismic moment

Answer 12

• M0 = μ A u
• A is area, μ is shear modulus of rocks, u id average displacement
• used to measure the elastic energy released
• preferred scale as works for range of magnitudes

Question 13

how much energy released increasing magnitude

Answer 13

roughly 30x energy released foe a +1 increase on magnitude scale

Question 14

what is the Mercalli scale

Answer 14

measure of ground motion nd resulting damaging effects