More about the Valentine's Day Earthquake and our probabilities

This recent 5.7 earthquake is a part of the aftershock sequence. This is the first larger earthquake since May 2012. So far, we have had 3,113 felt reports, as well as reports of liquefaction, subsidence (land slumping), rock falls and landslides.

GeoNet’s response and support for people in Canterbury

At GeoNet, we have been watching, recording and reporting these earthquakes for five years. We cannot provide assurance that this is the last we have seen of the earthquake sequence. In fact, our probabilities are now higher than before Sunday's earthquake. For quakes between magnitude 5.0 - 5.9, it has been increased from 49 to 63 percent and for magnitude 6.0 - 6.9, it has increased from 6 to 8 percent over the next year (more information below). Our priority continues to be the people of Canterbury. We support and deeply care about the people who are being affected by these earthquakes.  Providing the latest information to people in Canterbury is important to us.

As far as preparing, this is a good reminder for people to check their emergency supplies and that emergency plans are up to date. For more information about how to prepare for earthquakes, resources are available here:

Beyond physical preparedness is the emotional and psychological support for these earthquakes. The All Right? Hotline (0800-777-846) is a great resource where you can talk about any anxieties or concerns that you have regarding the earthquakes.

How long will the aftershocks last? It’s been five years!

Based on our modelling, there will be increased earthquake activity for decades in Canterbury.The way the sequence is decaying; this means it will likely take decades to return to the pre-Darfield activity levels. This long period of decay has been in our models and online probabilities since the Darfield earthquake in 2010.

For more information, have a look at our previous forecasts.

What will happen next?

We have updated our probabilities of larger or similar sized earthquakes. We cannot predict earthquakes. These probabilities describe the progression of the sequence in Canterbury within the next week, month and year. 

This earthquake has already produced 106 aftershocks. Most likely, these earthquakes will become less frequent over time. But people in Christchurch should be aware that there are going to be further earthquakes.

It is more likely than not that there will be another magnitude 5.0 – 5.9. This is the most likely scenario. However, we cannot rule out the possibility of larger earthquakes.

Here is a further breakdown of the numbers we’ve got aftershock probabilities for the Canterbury region in the next year:

  • It is likely (63%) that an earthquake of magnitude 5.0-5.9 will occur.
  • It is very unlikely (8%) that an earthquake of magnitude 6.0-6.9 will occur.
  • It is extremely unlikely (less than 1%) that an earthquake of magnitude greater than 7.0 will occur in the next year.

About our models

The Canterbury Earthquake sequence has been ongoing since 2010 and we have been modelling the earthquake sequence since that time. We have updated the current model with the new earthquake, and this model includes all the earthquakes that have occurred since the Darfield Earthquake.

This recent earthquake was within our model. At the time of the quake, there was a 49 percent chance of this earthquake happening, with the last forecast model run in November 2015. While Canterbury has been without severe intensity earthquakes since May 2012, this recent earthquake is a reminder that more magnitude 5.0-5.9 earthquakes are likely to occur.

Aftershock Region

Within this sequence, aftershocks will most likely occur anywhere in the box on the map (see image). It is this geographical region for which the modelling is done. It is important to understand that earthquakes can and do happen outside this box but the box represents the most likely area related to this sequence. While this recent earthquake and subsequent aftershocks were in Eastern Christchurch, this does not mean that any future earthquakes will stay or move further east. These earthquakes can occur anywhere in this “aftershock region”. 

We will update this information as required. 15/02/2016 1:30 p.m. 

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