Seismic Activity

Question 1

how are seismic waves created

Answer 1

when plates jerk past each other it sends out seismic waves

Question 2

what is the focus

Answer 2

the place in the lithosphere where the earthquake starts, seismic waves spread out from here

Question 3

what is the epicentre

Answer 3

the point on the earth’s surface where the earthquake is felt first, directly above the focus

Question 4

what are the 3 main types of seismic waves

Answer 4

• primary waves = p waves
• secondary waves = s waves
• surface waves = Rayleigh and love waves

Question 5

characteristics of p waves

Answer 5

• can travel through solids and liquids
• waves push and pull the earth in the same direction as the wave is travelling
• fastest type of wave
• 5000m/s rock(granite)
• 1450m/s liquid

Question 6

characteristics of s waves

Answer 6

• can travel through solids not liquids
• move the earth at 90oC to the direction of travel
• slower than p waves, 1/3 of p waves

Question 7

characteristics of love waves

Answer 7

• only travel through solids
• move the surface from side to side
• 90% of s wave velocity

Question 8

characteristics of Rayleigh waves

Answer 8

• can travel through solids and liquids
• move the surface in a rolling motion
• 90% of s wave velocity

Question 9

what can be used to measure earthquakes

Answer 9

seismometer,

Question 10

what do seismometers measure?

Answer 10

the magnitude of earthquakes - the amoint of energy they release. they also measure the duration and direction of the vibrations

Question 11

what are the two different scales to measure earthquakes?

Answer 11

the richter scale and the mercalli scale

Question 12

what does the richter scale measure

Answer 12

magnitude of an earthquake

Question 13

characteristics of the richter scale

Answer 13

• no upper limit, logarithmic (10x greater)
• each value represents about 30 times more energy released than the previous value
• don’t feel earthquakes at 1-2, major earthquakes are above

Question 14

what does the mercalli measure

Answer 14

the impacts of an earthquake

impacts are measured using observations

Question 15

what is the scale of the mercalli scale

Answer 15

1-12.
1 = earthquake only measured by instruments
12- earthquake causing total destruction

Question 16

what is a tsunami

Answer 16

large waves caused by displacement of large volumes of water

Question 17

how is a tsunami caused?

Answer 17

-triggered by underwater earthquakes
the earthquakes cause the seabed to move which displaces the water
-waves radiate out from the epicentre
-greater the movement of the sea floor, the greater the volume of water displaced - bigger wave produced

Question 18

what can cause a tsunami other than earthquakes?

Answer 18

volcanic eruptions and landslides that slide into the sea can displace large volumes of water

Question 19

characteristics of a tsunami in open, deep water

Answer 19

• high speeds, 500-950km/h
• long wavelength, 200km
• small amplitude, 1m

Question 20

what happens to the wave of a tsunami as it enters shallower waters

Answer 20

waves get compressed (squashed together) and their energy becomes more concentrated

Question 21

characteristics of a tsunami in shallower waters close to land

Answer 21

• slow down to less than 80km/h
• wavelength decreases to less than 20km
• amplitude increases to many metres

Question 22

what happens just before the tsunami reaches the coast

Answer 22

-water withdraws down the shore (is called drawback)

looks like the tide is going in