The expected probabilities (below) of further earthquakes cover the Canterbury region aftershock zone as indicated in the plot below. The numbers are based on the behaviour of aftershock sequences worldwide and the specific knowledge that scientists have of the Canterbury aftershock sequence since September 2010. The figures are generated from computer models that are updated as the aftershock sequence continues.
|Average number||Range||Probability of one or more||Average number||Range||Probability of one or more||Average number||Range||Probability of one or more|
|Within 1 year||0.6||0 - 2||45%||0.05||0 - 1||5%||0.005||0 - 1||<1%|
Issued on 1 September 2017 for the coming year.
This table shows an updated forecast based on a model from international expert elicitation. The forecast starts from 1 September 2017 and is for the region from 171.6-173.2 degrees east and 43.3-43.9 degrees south (see map).
As time passes the expected probabilities of earthquakes become smaller, but any further significant earthquakes that do occur will cause these probabilities to change. The magnitude categories illustrate clearly how the probability falls away as magnitude increases. The probability for an aftershock to occur decreases as magnitude increases, and a magnitude increase of one means a probability decrease of roughly 10 times. This means that a magnitude 7.9 earthquake is roughly 100 times less likely than a magnitude 6.0 earthquake and is therefore very unlikely. With every month that passes without a major aftershock, probabilities will continue falling. However, if another large aftershock occurs it can re-energise the system and spark a resurgence of earthquake activity for a month or so; this was seen with both the February and June 2011 magnitude 6.3 earthquakes. The maximum magnitude of an earthquake is also bounded by what scientists know about the size of faults in Canterbury. Scientists are currently not aware of any faults in Canterbury that are long enough to be able to produce a magnitude 7.9 earthquake. However, they cannot rule out this possibility with 100 percent certainty.
These figures are for the entire aftershock zone, not just for Christchurch city (see map for location of model).
|7.0 and above||1|
|6.0 - 6.9||2|
|5.0 - 5.9||34|
|4.0 - 4.9||383|
|3.0 - 3.9||3921|
|Earthquake Date/Time||Magnitude (Mw)||Location||Depth
|Distance from station recording
highest PGA to epicentre
|Sep 4 2010, 4:35:42 am||7.1||25 km south of Oxford||11||1.26||Greendale||9|
|Sep 4 2010, 4:37:03 am||5.8||25 km west of Christchurch||10||unable to be determined||-||-|
|Sep 4 2010, 4:37:36 am||5.5||25 km west of Christchurch||12||unable to be determined||-||-|
|Sep 4 2010, 4:52:56 am||5.5||20 km west of Christchurch||7||0.23||Rolleston School||2|
|Sep 4 2010, 4:59:20 am||5.5||35 km west of Christchurch||8||0.07||Lincoln Crop and Food Research||21|
|Feb 22 2011, 12:51:42 pm||6.3||5 km southeast of Christchurch||5||2.20||Heathcote Valley Primary School||2|
|Feb 22 2011, 1:04:19 pm||5.8||5 km southeast of Christchurch||6||0.93||Christchurch Cathedral College||6|
|Feb 22 2011, 2:50:30 pm||5.9||5 km south of Christchurch||7||0.76||Heathcote Valley Primary School||6|
|Jun 13 2011, 2:20:49 pm||6.4||10 km east of Christchurch||7||2.00||Godley Drive||3|
|Dec 23 2011, 1:58:38 pm||5.8||15 km east of Christchurch||10||0.98||New Brighton Library||6|
|Dec 23 2011, 3:18:04 pm||6.0||10 km east of Christchurch||7||0.66||Heathcote Valley Primary School||7|
|Jan 2 2012, 5:45:17 am||5.5||15 km east of Christchurch||12||0.21||Pages Road Pumping Station||18|
|May 25 2012, 2:44:49 pm||5.5||20 km east of Christchurch||12||0.17||Lyttelton Port Oil Wharf||17|
|Feb 14 2016, 1:13:43 pm||5.7||10 km east of Christchurch||8||0.36||New Brighton Library||8|