Seismic Hazards

Question 1

seismic hazards (5)

Answer 1

primary
shockwaves

secondary
tsunamis
landslides
liquefaction

Question 2

Types of seismic waves

Answer 2

Body waves
Primary (P waves)
- fastest
- solid and liquid
- least damaging

Secondary (S waves)
- slower
- solids only
- more damaging

Surface waves
Love (L waves)
- slowest
- side to side motion
- more destructive

Reylaigh

Question 3

tsunamis

Answer 3

triggered by underwater earthquakes
- moves seabed which displaces large volumes of water
- creates large waves

travel very fast
little warning

eg 2004 indian ocean

Question 4

Tsunami example

Answer 4

2004 Indian Ocean Tsunami
Final death toll - 283,000
Across many countries
1.7 million displaced

Spread of disease, contaminated water
Flooding - salinisation, loss of agriculture

Question 5

landslides / avalanche

Answer 5

shaking of ground can dislodge rocks, soil or snow
moves downslope quickly

shaking also loosens material
easier for water to infiltrate
weight of more water trigger landslide after event

eg Nepal - over 3000

Question 6

liquefaction

Answer 6

happens on saturated, uncompacted soil

vibrations cause it to act like a liquid
soil weaker (loses strength) and easier to deform

more likely to subside, especially under weight of buildings

Causes building and infrastructure collapse

eg Christchurch - 20,000 properties

Question 7

distribution

Answer 7

95% at plate boundaries

can help with prediction - know areas at risk

Question 8

magnitude

Answer 8

measured on rictor scale

destructive margins - higher magnitude
subduction zone causes massive pressure

deep focus - higher magnitude
but less damage as further from surface

Question 9

frequency

Answer 9

high magnitude happen less frequently
- need time for pressure to build up

many small magnitude ones happen very frequently

Question 10

randomness/ regularity

Answer 10

not clear pattern
unpredictable

Question 11

predictability

Answer 11

impossible to predict
- hard to evacuate and prepare

seismic gap help predict magnitude (longer gap = higher)
know areas at risk
can monitor local tectonic activity

Question 12

primary impacts

Answer 12

social
- building collapse, homelessness and death

economic
- destroy business

Question 13

secondary impacts

Answer 13

social
- lack of water, gas and power, damage
- spread of disease, often in shelters
- landslides

env
- tsunamis

political
- conflict and political unrest - lack of supplies

Question 14

short term responses

Answer 14

search and rescue
aid

Question 15

long term responses

Answer 15

reconstruction - life safe
review emergency plans
tsunami warnings
education

Question 16

preparedness

Answer 16

warning systems
- detect small seismic activity, may be indicator of larger one
- but very short notice

evacuation plans
education in schools

tsunami wanring systems

search and rescue

Question 17

mitigation

Answer 17

emergency plans in place

search and rescue prepared

life safe buildings

Question 18

prevention

Answer 18

not possible

prevent risk
- not build on land pine to liquefaction
- sea walls for tsunamis

Question 19

adaptation

Answer 19

life safe buildings
- designed to withstand shaking

also less vulnerable to tsunamis
- tall and strong

Question 20

Are tsunamis or earthquakes on land worse?

Answer 20

2004 Indian Ocean Tsnumai
283,000 deaths
Disease and loss of agriculture

Nepal
9000 death

Tsunamis worse
But less frequent than land earthquakes, narrow coastal belts they can effect

Question 21

Conservative

Answer 21

Shallow (no subduction)
Narrow zone
Low frequency (friction, pressure builds up)
Hugh magnitude

Question 22

Constructive

Answer 22

Shallow
Narrow
Regular
Low magnitude (as more frequent)

Question 23

Destructive subduction

Answer 23

Deep
Wide
Infrequent
High magnitude

Question 24

Destructive collision

Answer 24

Shallow (no subduction)