A Level Geography - Tectonics Questions
With reference to earthquake (seismic) waves, explain two
reasons why it is difficult for buildings to remain intact during an
earthquake. (4 marks)
One reason why it may be difficult for buildings to stay up
during an earthquake is the secondary love waves, which moves side to side.
These waves can be very damaging to the foundations of structures because of
their movement, making buildings fall as their bases can no longer support this
weight above.
A second reason which causes buildings to collapse during
earthquakes is the damage that primary seismic waves can do. They move away
from the source of the earthquake, pushing and pulling rock. This can cause
soil to compress, making the ground fully saturated with water. The soil
becomes weaker and so may not be able to support the buildings above it, thus
making them fall.
Explain the link between plate boundary type and the strength of
the earthquake (seismic) waves. (6 marks)
The strength of an earthquake can depend on the plate boundary
type. As an example, convergent plate boundaries produce much stronger
earthquakes as the plates are moving towards each other, which creates much
shallower earthquakes. Because the focus is not very deep, it means that the
waves do not have far to travel and so do more damage when they reach the
surface. Divergent plate boundaries usually produce very low magnitude
earthquakes as there is little pressure built between the tectonic plates as
they move apart, not towards one another.
Different plate boundaries can cause the depth of the
earthquake's focus to change. Deeper earthquakes mean that the seismic waves
have longer to travel to reach the surface which means they lose some of their
power. This makes earthquakes like this have a lower magnitude on the Richter
scale than earthquakes with a focus that is more shallow. Shallower earthquakes
have more devastating effects on the area above as the seismic waves are
stronger and therefore produce more vigorous shaking.
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