Earthquakes Flashcards
cratons
stable portions of the continental crust no longer tectonically active, often ancient and described as continental shields
What are aseismic zones?
areas with no stresses to cause dislocation and earthquakes
Where do you get shallow earthquakes? 4
MOR
axial rift
transform fault
constructive margin
Where do you get deep- intermediate earthquakes? 3
benioff zone
deep ocean trench
fold mountains
describe the role of the asthenosphere in mantle convection?
the asthenosphere is rheid so it can flow very slowly and may allow convection. This layer acts as a ‘lubricant’ which allows the lithosphere to move across
What evidence is there for mantle convection?
new crust at the MOR
Magnetic stripes at MOR
Why is there no earthquakes deeper than 720km?
the hot rocks are too ductile to cause earthquakes
Why are there different rates in movement along a fault?
Along the fault there are different types of rock. Soft rocks have little friction so can move past each other more easily. Hard, more competent rocks have more friction so store more stress.
How do seismometers work?
When vibrations pass the seismometer all the parts of the apparatus move and vibrate except the heavy suspended weight. This is either attached to a pen or an electronic plotter which produces a wavy trace on a rotating drum or paper roll.
What is a seismogram?
These are paper traces produced by the seismometers and they record the arrivals of P, S and L waves.
What are P and S waves
body waves
What are L waves
surface waves
How do we find the epicentre of an earthquake?
We ask people to rate the damage/ what they felt on the Mercalli scale which measures intensity. The Richter scale can then be used to measure magnitude
How can P and S waves be used to determine the size and state of the outer core?
s wave shadow zone between 103 to 142 degrees
s waves cannot move through a liquid
Very strong L waves occur at the …..
epicentre 0 degrees
