Earthquake update – Thursday

Geonet 5 am Thursday update:

  • 19 earthquakes in last hour
  • 290 earthquakes in last 12 hrs (11 over M4)
  • 2070 earthquakes since the M7.8 (570 since 4 am Wednesday)

The rate and size of quakes is slowly reducing. The larger quakes overnight:

  • 4.3 – 7:45:51 pm 20 km south of Seddon
  • 4.3 – 7:46:33 pm 20 km north-east of Kaikoura
  • 3.8 – 9:27:10 pm 5 km north of Culverden
  • 4.8 – 10:15:14 pm 20 km east of Martinborough
  • 4.3 – 1:19:45 am 30 km north-east of Arthur’s Pass
  • 3.8 – 3:20:09 am 25 km north-east of Hanmer Springs
  • 4.0 – 3:41:33 am 30 km south of Seddon
  • 4.9 – 4:03:49 am 20 km south-west of Kaikoura
  • 4.0 – 5:02:32 am 10 km north of Culverden

Notable points: while reducing in size they are still spread over the three main areas, Culverden/Hamner, Kaikoura and Seddon, but with two other locations, east of Martinborough on the Wairarapa faultline (the one that went M8+ in 1855) and one north-east of Arthur’s Pass (Alpine Fault territory).

We can hope that these are reducing stresses rather than increasing them on other faultlines.

Yesterday Geonet upgraded the size of the initial quake (which may have been two consecutive quakes in different locations) from M7.5 to M7.8.

Kaikoura earthquake update: Magnitude revised

What has changed since our initial review

Based on our findings and in discussion with international researchers, early indications are that this is one of the most complex earthquakes ever recorded on land. This complexity means we have had to take extraordinary efforts to determine the magnitude, depth, and locations.

The very long time it took for the faults to rupture (over one minute) meant that the standard methods of calculating magnitude were insufficient to capture the full energy released.  

Due to the size of the quakes, we’ve gathered data from our entire network of seismic stations. All of these stations would not normally need to be included in magnitude estimates.

Further, our techs at GeoNet went out to several sites which we lost communication with and we have now been able to upload this information, so we have a more complete understanding of the ground deformation and strong-motion data.

Finally, our science teams have been working tirelessly, going up and down the affected areas and measuring the length of faults and how much they moved.  Their efforts have provided us with a clearer picture as to the size and length of the ruptures.

Based on all these ongoing efforts, we can say with some confidence that the earthquake was an M7.8.  This is consistent with estimates from several  other international agencies, specifically the USGS. Their early model provided us important information and we used all our additional data sets to confirm the magnitude. 

What this means

The new magnitude just tells us what we think most people who felt the earthquake already know: it was powerful, and went on for a long time over a large distance. It doesn’t change what happened but it does provide us with more knowledge about how significant the event was.

Our recent analysis confirms the complexity of this event. It does not change any of the observations of strong ground motion, fault breaks or GPS recorded movement of the earth’s surface – these are physical observations independent of the magnitude of the earthquake.

We are in the process of revising our probabilities and scenarios based on this new information and should have this released within the next 24 hours.

RNZ continues to have good coverage, including:

Rescue efforts in Kaikoura continue as helicopters and NZ and US defence force ships arrive in the quake-hit town with supplies.

Wellington is also dealing with the aftermath of Monday’s 7.8 magnitude quake, with several central city buildings deemed unsafe.

The aftermath of the 7.8 magnitude quake so far

Govt to consider funding for 24/7 quake monitoring

‘Absolutely gutted’: Tiny community of Mt Lyford devastated by quake