Hazards resulting from tectonic processes

Question 1

Explain two reasons why intensity of ground shaking varies

Answer 1

• The higher the energy released, the greater the ground shaking. The 2011 Tohoku earthquake in Japan had a magnitude of 9.0. The epicentre of the earthquake was located off the coast of Japan, and the ground shaking was felt as far away as China and Russia. The intensity of the ground shaking was greatest near the epicentre, and it decreased with distance
• Energy is absorbed, particularly by solid geology, as shock waves radiate outwards from the epicentre in all directions, so intensities of ground shaking decrease with distance. This wasn’t the case in Japan as the energy was too great to be absorbed and caused a seabed to rise up.

Question 2

Explain why the depth of earthquakes varies from place to place.

Answer 2

• Transform faults tend to produce shallow focus earthquakes. This because the faults provide a weak zone where the rocks can break more easily.An example is the San Andreas fault which is a transform fault that produce shallow earthquakes.
• Collision boundaries tend to produce shallow earthquakes because of no subduction. An example is the The Himalayas which are a collision zone that produces relatively shallow focus earthquakes