Seismic Hazadds Flashcards
What is the epicentre in an earthquake
The point directly above the focus on the surface
What is the focus in an earthquake
Where the earthquake originates in the earth’s crust
What does being closer to the epicentre mean for buildings and people
Closer to epicentre - more damage
What are the steps to seismic waves
Pressure builds at the point where two points meet
Sudden release due to rock failure creates waves
These waves cause the groud to shake
This causes earthquakes
What are the 4 seismic wave types
P wave
S wave
Rayleigh wave
Love wave
What sre the features of a p wave
Short pulse of energy moving the groud forwards and backwards
Fastest moving
Least damaging
Ehay sre the features of an s wave
S waves move the group and down
More damaging than p waves
Slightly slower than p waves
What are the features of a Rayleigh wave
Rayleigh waves go up and down
Slower than s waves
Damaging to buildings because they are slower
What are the features of a love wave
Move the ground sideways
Relatively slow
The most damaging
How are tsunamis formed (simple)
Most commonly by destructive plate boundaries in the ocean which creates earthquakes when the overriding plate snaps back
Pressure is released - rapid movement of ocean floor displaces a column of water
Series of small heighted waves travel across open ocean
Energy compresses as it reaches the shore and small waves become one big wave -water retreats from shoreline
What is liquefsction
Liquefaction- mixing of sand/soil and groundwater
When water and soil mix the ground becomes very soft
If liquefaction causes some buildings to tip or sink
The ground firms up as groundwater retreats after an earthquake leaving the buildings ajar
What are landslides and how do they occur
Grounshaking because earthquakes destabilises cliffs and causes landslides
Heavy rain or unconsolidated rock make this more likely
What are three ways to predict earthquakes
Seismic records
Radon gas emissions
Remote sensing
How can looking ast seismic records help predict earthquakes
Seismologists are able to see if earthquakes are more likely to strike by calculating probabilities and forecasts
How can remote sensing help us predict earthquakes
Often an increase in surface and near surface temperature before an earthquake - ir satellite can record thermal anomalies
Sometimes gas and aerosol content change before an earthquake
How can remote sensing help us predict earthquakes
Often an increase in surface and near surface temperature before an earthquake - ir satellite can record thermal anomalies
Sometimes gas and aerosol content change before an earthquake
How can radon gas emissions help us predict an earthquake
Radon is released from cavities and cracks as the earth’s crust is strained prior to the sudden slip of an earthquake
What are some primary effects of an earthquake
Liquefaction of saturated soils
Panic , fear and hunger
Schools destroyed
Damage to power stations
Buildings/bridges , power lines , water mains , gas mains and sewers collapse -
Immediate deaths from injuries such as crushing
What are some secondary effects of an earthquake
Bodies not disposed of properly spread diseases like cholera
Fire caused by broken gas pipes are difficult to put out
Flooding from blocked rivers create “quake lakes”
Looting and civil disorder
Power cuts restrict immediate medical care
Education suspended for immediate future
Slope failures setting if landslides and avalanches
What are some long term effects of an earthquake
Reconstruction of power stations may take long as its very expensive
Long term “lost generation “ ti develop local / regional economy
Loss of farmland and food production
Higher unemployment as businesses might not recover
Trauma and grief may take years to recover
Problems restoring trust in neighbours and civil authorities
What is the Mercali scale and what is it useful for
A subjective view of an earthquakes effects and useful for judging the necessary response to an earthquake
What is the richer scale
A scale which measures the ground deformation and energy release caused by and earthquake
Why do scientists use the richer scale and not the mercali scale
The richer scale is completely unbiased while the mercali scale may change from person to person
