Seismic Hazards Flashcards
seismic hazards (5)
primary
shockwaves
secondary
tsunamis
landslides
liquefaction
Types of seismic waves
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
tsunamis
triggered by underwater earthquakes
- moves seabed which displaces large volumes of water
- creates large waves
travel very fast
little warning
eg 2004 indian ocean
Tsunami example
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
landslides / avalanche
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
liquefaction
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
distribution
95% at plate boundaries
can help with prediction - know areas at risk
magnitude
measured on rictor scale
destructive margins - higher magnitude
subduction zone causes massive pressure
deep focus - higher magnitude
but less damage as further from surface
frequency
high magnitude happen less frequently
- need time for pressure to build up
many small magnitude ones happen very frequently
randomness/ regularity
not clear pattern
unpredictable
predictability
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
primary impacts
social
- building collapse, homelessness and death
economic
- destroy business
secondary impacts
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
short term responses
search and rescue
aid
long term responses
reconstruction - life safe
review emergency plans
tsunami warnings
education
preparedness
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
mitigation
emergency plans in place
search and rescue prepared
life safe buildings
prevention
not possible
prevent risk
- not build on land pine to liquefaction
- sea walls for tsunamis
adaptation
life safe buildings
- designed to withstand shaking
also less vulnerable to tsunamis
- tall and strong
Are tsunamis or earthquakes on land worse?
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
Conservative
Shallow (no subduction)
Narrow zone
Low frequency (friction, pressure builds up)
Hugh magnitude
Constructive
Shallow
Narrow
Regular
Low magnitude (as more frequent)
Destructive subduction
Deep
Wide
Infrequent
High magnitude
Destructive collision
Shallow (no subduction)