Hazards- Seismic Hazards

Question 1

Seismometers

Answer 1

• used to measure earthquakes

- used to plot seismographs which are then read to determine how much shaking occurred

Question 2

Modified Mercalli Scale

Answer 2

• lower numbers of intensity deal with the manner in which the earthquake is felt by people
• higher numbers based on observed structural damage
• structural engineers contribute to info when intensity values of 8 or above are assigned
• uses qualitative data- based on people’s opinions and observations

Question 3

Richter Scale

Answer 3

• measures the ground deformation and energy release by an earthquake
• scale is logarithmic eg. 3 is 10x greater than 2
• quantitative data

Question 4

Seismicity

Answer 4

The Earth shaking- can be human induced (eg. via reservoir construction, fracking or mining)

Question 5

P waves

Answer 5

• push motion causes expansion and compression of material
• not a continuous motion
• fastest moving waves
• moves through solids and liquids
• backwards and forwards movement

Question 6

S waves

Answer 6

• vertical movement
• slower motion
• shaking Earth at 90 degrees
• can’t move through liquids
• does more damage than P waves

Question 7

Rayleigh waves

Answer 7

• slow movement
• continuous movement
• radiate along the surface in low frequency rolling motion

Question 8

Love wave

Answer 8

• horizontal movement
• surface waves are slowest
• cause sideways motion
• cause most damage

Question 9

What is the cause of a tsunami?

Answer 9

• caused by earthquakes
• generated in subduction zone (oceanic plate forced down into mantle)
• powerful volcanic eruption can also cause one

Question 10

How do tsunamis travel?

Answer 10

Travel swiftly across open ocean

Question 11

What is the tsunami “wave train”?

Answer 11

• tsunamis consist of multiple waves

- shoreline pounded by repeated large waves

Question 12

How is a tsunami formed?

Answer 12

• rapid movement of the ocean floor displaces a column of water
• series of waves travel outward at heights believed to be less than three feet on the open ocean
• as the wave approaches land, it’s energy compresses into a smaller space, forcing it to gain height

Question 13

Liquefaction

Answer 13

• soil liquefaction causes building to sink into the ground
• the mixing of sand/soil and groundwater during an earthquake
• ground becomes very soft
• it is a hazard in areas that have groundwater near the surface and sandy soil

Question 14

Landslides

Answer 14

• ground shaking (due to earthquakes) destabilises cliffs and steep slopes
• causes landslides and rock falls
• also caused by heavy rainfall and rock features
• especially common in highland areas (sit on unstable plate boundaries)