Seismic Hazards

Question 1

Seismicity

Answer 1

Earth shaking

Can be human induced through fracking, mining and reservoir construction

Question 2

Earthquake Formation

Answer 2

Friction along margins = stress in lithosphere
Stress suddenly overcome
Plates fracture along faults
Sends a series of shock waves to the surface
Tremors can be followed be several weeks of after shocks whilst crust settles

Question 3

What factors make the damage done by an earthquake worse?

Answer 3

Time of day
Depth of focus
Population density 
Level of development 
Building quality

Question 4

P Waves

Answer 4

Fast moving, first to reach the surface
Travel through solids and liquids (crust, mantle, core)
High frequency

Question 5

S Waves

Answer 5

Second waves to reach the surface
Travel through liquids (mantle)
Sideways movement, shaking earth at 90° to direction of travel
Do more damage than P waves

Question 6

Love Waves

Answer 6

Slowest moving

Do most damage because of sideways movement

Question 7

Rayleigh Waves

Answer 7

Radiate from epicentre in complicated, low frequency rolling motions

Question 8

Tsunami

Answer 8

Large sea wave generated by earthquakes on the ocean floor, large landslides and submarine volcanic eruptions

Question 9

Tsunami Formation

Answer 9

Pressure between 2 plates suddenly released
Large waves of energy displace water
Water train created, spreads in concentric circles to shore
Upon reaching shore, wave shoaling occurs (friction = highly destructive wave)
Wave retreats taking debris, forming the next wave

Question 10

What factors make the damage done by a tsunami worse?

Answer 10

Distance travelled
Focus depth (shallower = larger)
Population density 
Level of development 
Warning given

Question 11

Landslide

Answer 11

Movement of rock, debris or earth down a slope

Question 12

Landslide Formation

Answer 12

Ground shaking due to earthquake destablishes cliffs and steep slopes
Causes material to quickly move down slope

Question 13

What factors make landslides worse?

Answer 13

Steep gradient
High relief rainfall (saturates ground = unstable)
Shallow soil
Unstable rock

Question 14

Liquefaction

Answer 14

Jelly like state of silts and clays resulting from intense ground shaking

Question 15

Liquefaction Formation

Answer 15

Sand or soil mixes with ground water

Becomes very soft, causing subsidence and building collapse

Question 16

What factors make liquefaction worse?

Answer 16

High ground water
Reclaimed soil
Sandy soil (loosely packed grain = more pore spaces to fill with water)

Question 17

Richter Scale

Answer 17

Logarithmic
1 to 10+
Easy comparison between disasters
Quantitative

Question 18

Modified Mercalli Scale

Answer 18

Qualitative
0 to XII
Different levels for different areas
Only useful with buildings around

Question 19

Preparedness: Name some of the events that occur in the minutes before an earthquake

Answer 19

Microquakes before main tremor
Magnetic changes in local rock
Unusual animal behaviour

Question 20

Prevention: Although almost impossible to prevent, what have some scientists suggested?

Answer 20

Putting water and oil in margins
Lubricates movement
Plates will slide not stick

Question 21

Adaptation: What form does protection mainly take?

Answer 21

Preparation by modifying the human and built environments to decrease vulnerability and reduce loss

Question 22

Adaptation: 2 features of hazard resistant structures

Answer 22

Concrete weight on roof- moves in opposite direction to force of earthquake, counteracting stress
Rubber shock absorbers in foundations- allows some movement

Question 23

Adaptation: What can people in old buildings do?

Answer 23

Retrofit them to make them more aseismic

Question 24

Mitigation: How does education help?

Answer 24

Minimises loss of life, through earthquake drills

Question 25

Adaptation: 2 ways fires can be prevented

Answer 25

Smart meters- cut off gas in an earthquake over a certain magnitude Tokyo gas companies- switch off pipelines, reducing the number of fires

Question 26

Adaptation: 2 ways of protecting against tsunamis

Answer 26

Tsunami warning systems | Build 12m high tsunami walls (ineffective)

Question 27

Protection: How can the emergency services be ready?

Answer 27

Heavy lifting gear available Carefully organised and planned response People in communities given first aid training to treat injured before help arrives

Question 28

Mitigation: Why are people urged to take out insurance in richer countries?

Answer 28

To cover their losses- expensive

Question 29

Adaptation: Land use planning

Answer 29

Schools and hospitals built in low risk areas | Green space put into high risk areas, forming a safe area away from fires and aftershock debris + distribution areas

Question 30

Prevention: How can any impacts from liquefaction be prevented?

Answer 30

Authorities preventing building on land prone to liquefaction

Question 31

Mitigation: How to earthquake and tsunami warning systems reduce damage caused?

Answer 31

Detect weak shockwaves TV / SMS warnings given Aids evacuation