New research into the events leading up to the 2016 Kaikoura earthquake could offer a different approach to forecasting earthquakes. The research conducted by Victoria University geophysicist associate professor Simon Lamb found that most earthquakes that occurred on a fault line were triggered by earthquakes on faults elsewhere.
“It has been commonly thought that that best way to predict future earthquakes is to analyse the earthquake histories of individual faults,” Mr Lamb said.
“This method assumes that each fault has its own in-built pacemaker or mechanism, giving rise to semi-regular earthquakes on the fault.”
Mr Lamb says there are a number of issues with this method, such as the vast number of faults, some of which are not visible at the surface.
Mr Lamb says the team looked at the slow movements of the landscape in the two decades leading up to the 2016 Kaikoura quake, measured with precise satellite mapping of ground motions.
“We found that the measured ground motions were caused by slippage only on the single major fault line separating the two tectonic plates that lie under New Zealand.
This large fault, called megathrust, underlies much of New Zealand and only reaches the surface offshore.”
The megathrust moves freely at depths of 30 kilometres but shows no movement at levels closer to the surface.
This creates an elastic-like movement, causing extreme stress on the landscape and in this case causing the 2016 quake.
“The Kaikoura earthquake initiated a complex pattern of fault movement, essentially shattering the landscape, and causing a cascade of earthquakes on 20 or more faults,” Mr Lamb said.
“The data we studied show a strong link between the pattern of shattering and locking of the underlying megathrust prior to the earthquake and the movement during the earthquake itself.
The damage caused by the Kaikoura earthquake runs parallel to this locking of the megathrust, but cuts across many of the big surface faults in the area, indicating a strong link to the movement of the megathrust rather than any of the individual faults.”
The findings could now be significant in predicting future earthquakes.
“While we may not be able to predict the movement of individual faults, we can track the underlying cause of an earthquake and give an indication of where future shaking might occur by understanding and modelling the megathrust.”