Seismicity - Causes of Earthquakes Flashcards
What builds up within rocks?
stress
What happens when pressure is released suddenly?
intense shaking that lasts a few seconds
What is the focus?
the point where the pressure is released within the crust
What is the epicentre?
the point immediately above the focus on the earths surface
What are other causes of earthquakes?
reactivation of old fault lines, subsidence, pressure on surface rocks
What is the depth of a shallow-focus?
0-70km deep
What is the depth of a intermediate focus?
70-300km deep
What is the depth of a deep focus?
300-700km deep
What focus causes the greatest damage and what % does it account for all earthquake energy released?
shallow-focus, 75%
Whats another name for P waves?
primary waves
Whats another name for S waves?
secondary waves
Whats another name for L waves?
surface waves
How fast do P waves travel?
5.5km/second
Which direction do P waves vibrate?
in direction of travel
What can P waves travel through?
solids and liquids
Are P waves compressional?
yes
What speed do S waves travel at?
3km/second
Which direction do S waves vibrate?
at right angles to the direction of travel
What can S waves travel through?
only solids
Do L waves travel near the grounds surface?
yes
In which direction do L waves vibrate?
at right angels to the direction of the wave
What type of wave is the most damaging and why?
L waves, they travel up and down and side to side
Do L waves travel quickly?
no they travel slowly near the grounds surface
What are the slowest waves and in which direction do they move?
Rayleigh waves, move in a rollin motion
Where do most earthquakes occur?
along plate boundaries
Which plate boundary are the most powerful earthquakes associated with?
convergent plate margins
What happens at conservative margins?
the boundary is marked by a fault a movement along it causes an earthquake e.g.. San Andreas fault
