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The Cook Strait earthquake sequence is generating hundreds of aftershocks, although most of them are not felt. What are the numbers so far?


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Below is a comma separated variable file of earthquake locations since the sequence began on Friday 19 July 2013 through until Wednesday 6 August 2014. It is easily read by most common spreadsheet programs such as Excel and Open Office. NB: The earthquake times are in Co-ordinated Universal Time (UTC). Or you can download an up-to-date copy yourself!

  File Modified
Microsoft Excel Sheet quake_20140806_1140.csv Aug 06, 2014 by Kevin Fenaughty

What are the probabilities of future significant earthquakes?

The table below summarises the expected probabilities of further earthquakes anywhere in the central New Zealand region shown on the accompanying map. This is an increase over and above what is normal seismicity for this part of New Zealand. The figures are based on the behaviour of aftershock sequences worldwide and the specific knowledge that scientists have of the Cook Strait sequence so far. The figures are generated from computer models that are updated as the sequence continues. It shows that as time passes these probabilities 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.

 


 

M4.0-4.9M5.0-5.9M6.0-6.9M ≥7.0

Average
number

Range*

Probability of
one or more

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 30 days

1

0 - 4

75%

0.10 - 1

12%

0.010 - 1

1%

0.0010 - 1<1%

Within 1 year

11

5 - 18

>99%

10 - 3

65%

0.10 - 1

9%

0.010 - 11%

Issued on 1 June 2014 for the coming month.

On 1 June the probability of a magnitude 6 or above in the next year in this region is approximately two times greater than what we would normally expect from our National Seismic Hazard model due to this sequence. As the aftershock rates decrease, this difference will decrease as well.

* 95% confidence bounds.

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You can watch a video of seismologist Matt Gerstenberger using Christchurch events to explain how our earthquake probabilities are made.

What are the ten largest earthquakes so far?

MagnitudeDepth (km)Date
6.68

2013-08-16 14:31

6.5132013-07-21 17:09
6.0142013-08-16 17:31
5.8202013-07-21 07:17
5.7172013-07-19 09:06
5.6192013-08-16 15:51
5.582013-08-16 15:09
5.5202013-08-16 18:55
5.5202013-08-17 20:58
5.492013-08-16 14:37
This table was last confirmed on 6 August 2014 AM

How many have there been?

Numbers of Cook Strait region earthquakes

Magnitude range7 am, 19 July 2013 to
2:30 pm, 16 August 2013
2:30 pm, 16 August 2013 to
11:40 am, 6 August 2014
Total
6.0 - 6.9123
5.0 - 5.961521
4.0 - 4.9*7374147
3.0 - 3.9*450460910
2.0 - 2.9*211535155630
TOTAL264540666711

* Due to the complexity of the bigger earthquakes, numbers of these smaller earthquakes will be underestimated

This table was last updated on 6 August 2014 AM
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