Geography – Earthquake and volcanic hazards and impacts | e-Consult

The depth of the earthquake's focus (hypocentre) is a crucial factor influencing the intensity of shaking felt at the epicentre. Shallower-focus earthquakes (depths of 0-70km) generally cause greater damage than deeper-focus earthquakes (depths of 70-700km). This is because seismic waves have less distance to travel to reach the surface.

Ground Shaking: As seismic waves travel upwards, their energy is released. Shallower foci mean the waves encounter less rock to dissipate their energy, resulting in stronger ground shaking at the surface. Deeper foci experience greater attenuation (weakening) of the waves as they pass through the Earth's layers. This leads to weaker ground shaking at the epicentre.

Damage: The intensity of ground shaking directly correlates with the potential for damage. Stronger shaking can cause widespread structural failure in buildings, landslides, and liquefaction of soil. Shallower earthquakes are therefore more likely to cause significant damage to infrastructure and human settlements. Deeper earthquakes, while potentially still causing damage, are less likely to result in the same level of destruction.

Furthermore, the distance from the focus also plays a role, but the depth is a primary determinant of the intensity experienced at the epicentre. A shallow earthquake closer to a populated area will likely cause more damage than a deeper earthquake at a greater distance.