Earthquakes Flashcards
What is the sequence of an earthquake
There is a gradual build up of pressure in crustal rock
When the build up of pressure exceeds the strength of the fault, the rock fractures
The sudden fracture releases lots energy, creating seismic waves which radiate away from the point of fracture
Waves reach the surface in the form shaking
What are the primary impacts of earthquakes
Crustal fracturing - craters in the land
Ground shaking - collapse buildings
What are the secondary
Impacts of earthquakes
Landslides, and avalanches
Liquefaction - solid materials behave like liquid
Tsunamis
What plate margins cause the most powerful earthquakes
1.) conservative - shallow focus and very powerful
2.) destructive - deep focus and powerful
3.) constructive - shallow and not as powerful
What are primary waves
Arrive first, move through solid rock and liquid
What are secondary waves
Arrive next, slower the P waves, only move through sold rock
What are Rayleigh waves
Only travels through the surface of the crust, responsible for the shaking feeling
What are love waves
Only travels through the surface of the crust, fastest of the surface waves
What are the physical factors that can affect earthquakes
Geology
Depth of focus
Location of epicentre
Type of boundary
How does geology affect earthquakes
Nature of the ground can impact how much damage is caused
Loose, sandy soil can liquify if shaking is strong enough - Mexico City - 1985 - mag 8
How does the depth of focus affect earthquakes
Shallow depths mean more damage - seismic waves have to travel less distance
How does the location of the epicentre affect earthquakes
Epicentre is the point right above where the earthquake originates
If near built up areas can cause lots of damage - haiti - Port au Prince was 25km from epicentre
How can the type of boundary affect earthquakes
Destructive plate margins produce a higher magnitude
Conservative plate margins also have high magnitudes
9.5 mag in chille 1960
What methods can be used to monitor earthquakes
Tiltmeters - detect changes in ground height
Seismometers - detect micro quakes prior to big event
Water measured for radon gas - changes in the water table can indicate and earthquake
Unusual animal behavior - some animals seem to be able to sense events before it happens
Outline the process of liquefaction
Occurs when compacted sediment loses strength and stiffness due to an applied stress from earthquake shaking
Make solid material behave like a liquid
However liquefaction requires a degree of soil saturation to occur
Causes buildings to collapse as well as sink holes open up, endangering lives and infrastructure
What are the primary
effects of earthquakes
infrastructure damage
Building damage
Injury/loss of life
Displacement of population
What are the secondary effects of earthquakes
Environmental degradation
Health issues - disease outbreak
Fires
Economic issues
Social issues
How can the impacts of earthquakes be mitigated
Deep building foundations
Using suitable building materials
Damping systems - prevents oscillation
Base isolation systems - separates the structure from its base - energy can’t be transferred up the building
