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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