The severity of earthquake hazards depends on the strength and depth of the earthquake, but there are several other contributing factors.
The regional geology, local topography and the site-specific ground characteristics all influence how earthquake effects will manifest at a given location.
Lessons learned from recent earthquakes in New Zealand show that the topography of a building site can have a significant effect on the degree of damage resulting from an earthquake. Dwellings built on flat land with no liquefaction issues were observed to have less damage in an earthquake than buildings on hill ridges and steep slopes.
In its guidance Repairing and rebuilding houses affected by the Canterbury earthquakes, MBIE states, “Hillside properties in general are more complex than level-ground properties and do not lend themselves easily to a standard approach with regard to foundations and stability issues.”
Studies of past events also show that the local ground conditions significantly affect the type and degree of damage a building is likely to sustain in an earthquake.
The severity of the ground shaking hazard at any given site depends on several factors, including:
- energy of the seismic waves (amplitude, frequency and duration)
- distance from the event epicentre
- depth, density and type of soil between the structure and the bedrock
- local geographic features.
Some types of ground, such as soft or deep soil, can exacerbate the shaking of taller structures.
This is why it is important to properly assess and design an intended building type for the ground conditions at each specific building site.