The truth behind earthquake prediction

Earthquake prediction is the holy grail of seismology – it would save lives. Accordingly, a lot of time and money has been invested in it over the last 200 years, but despite best efforts it’s still not possible to predict an earthquake and some doubt whether it ever will be. Nevertheless, the quest continues. So let’s take a look at the current science.

An earthquake probability can be thought of in the same way as a weather forecast – they both give the chance of something happening in a certain place within a certain time frame. They provide an indication of what's to come, but not certainty. For example, a weather forecast might say - ‘70% chance of rain in Westport today’, giving us the probability of an event within a certain timeframe in a certain location. An Earthquake Probability or Forecast says: ‘75% chance of a rupture on the Alpine Fault in the next 50 years’ – event, probability, timeframe, place.

Once the probability reaches 100% (or very close) then a forecast can be considered a prediction – scientists are working hard to increase the probabilities all the time. You can read more about earthquake forecasting in New Zealand at GeoNet. As you can see, a forecast is made up of a few different elements – Where, When, and How big. Lets look at each separately.

As almost all earthquakes happen on faults, having a good map of active faults really helps predict where earthquakes will happen. GNS Science maintains a database of active on-land faults in New Zealand, you can check out the interactive version here.

Unfortunately, creating an accurate map of all the faults in an area is not as simple as it sounds. The Earth’s history spans billions of years, and even on the best-preserved faults (such as the Alpine Fault) there is only evidence for the last few thousand years, which is just the blink of an eye in our planet’s lifespan.

That means that some faults may be ‘invisible’ until an earthquake happens. It may be that they rupture infrequently (like once every thousand years), or they run through an area of high erosion. This was the case for the fault that caused the destructive 2010 Darfield Earthquake – the braided rivers of the Canterbury plains had erased evidence of previous ruptures.

And even on faults that scientists do know a lot about, like the Alpine Fault, there is still the question of which part of the fault will rupture? The Alpine Fault is ~600km long and its next earthquake could start anywhere across that distance! But slowly a more accurate picture of our faults is building. Each little piece of information adds something, about where they occur and how they behave, and it is these behaviour patterns which lead us on to the When.

The Alpine Fault is currently as good as it gets anywhere in the world for using recurrence intervals to predict timing of earthquakes. But it’s not good enough to form a prediction, geological time is just too big and human timescales too small. However, this evidence and other research has enabled scientists to work out the probability of the next Alpine Fault earthquake and recent calculations indicate there is a 75% chance of an Alpine Fault rupture in the next 50 years (read more here)

Added to real-life data from faults is data from lab-induced earthquakes. In this video, Marie Denolle, a seismologist from Harvard University, explains how her team has managed to predict aftershock sequences in the laboratory using computer modelling and AI.

While scientists aren’t yet at the point where they can predict future earthquakes in real-life, they can let you know very quickly once it’s started. Introducing…. Earthquake Early Warning systems.

Earthquake Early Warning (EEW) systems are for after an earthquake has started and rely on the fact that telephone and internet communications travel faster than seismic waves. Obviously, if you are very close to the epicentre the warning won’t be much use, but it could give people anything from a few seconds to a few minutes of warning to prepare. Japan and the USA currently have EEW systems in place and researchers at Massey University have been investigating how they could be implemented in New Zealand.

Google is also currently trialling an early-warning system in New Zealand using the accelerometers in people’s smartphones. The idea is that the phones will sense a strong motion and send out an automated alert to others on the network (read more here).