LIVE UPDATES: Seismic activity meeting
Fri, 06 Jan 2012 11:57a.m.
By James Murray
Our live stream is currently experiencing very high traffic. If you are unable to watch please completely exit your browser and then reopen - this should make it work. We will also have the full meeting up as a video later today.
Three top seismologists from GNS Science will brief Christchurch Council officials and local MPs on the risks of further strong earthquakes today.
The meeting, which starts at 1pm today, was called by Christchurch Mayor Bob Parker after two strong aftershocks on Monday and the series of strong shakes, including a magnitude 6, on December 23.
New quake minutes after experts address
The meeting will be led by GNS Natural Hazards manager Kelvin Berryman and will also be attended by high up members of the emergency services.
“There’s such a wide spread of theories that are floating around the community at the moment," says Mr Parker.
"I think we need to bring the discussion back – a bit of clarity, a bit of direction and perhaps a better understanding about what the months ahead of us may actually hold in store.”
Mr Parker says the experts won't provide absolute answers, but will give an idea of the risk of seismic activity in the area.
Port Hills MP Ruth Dyson is also concerned at a lack of information.
She is seeking information for the Port Hills electorate regarding the rockfall risk, and general zoning and building decisions.
1pm - The meeting has just started and Mayor Bob Parker is opening up. He has welcomed Brownlee, Dyson, Wagner as local MPs at the meeting. Superintendent Gary Knowles of Pike River fame is also here as the new regional commander for the police. He has given the MPs the opportunity to add any extra information at the end of the meeting.
He is now introducing the panel - Kelvin Berryman who leads the GNS team overseeing ChCh , Stephen Bannister also from GNS Science and Jarg Pettinger from the Geological Science Unit at Canterbury University, Nick Rogers and Mike Jagger from engineering firm Tonkin and Taylor are also present.
Parker says he is not expecting to receive any "new pearls of wisdom" today, but is seeking to dispel rumours and misinformation that have circulate since the December 23 quake.
1:10pm - Mr Parker jokes that people have been making the suggestion that Cantabrians should all move to Dunedin, he says the only benefit that will bring is to help them pay for their new stadium and improve their rugby team.
Mr Parker says the people assembled are a very representative group for Christchurch and will ask all the relevant questions for people in the city.
Kelvin Berryman is now speaking. He is outlining who will speak about what at the meeting. He has a visual presentation to show people.
His first slide shows all the seismicity from September 4, 2010 to the end of December. He says the epicentre of the Darfield earthquake was just off the Greendale Fault - he says this was a complex quake which strained the structure of the earth so much that it was able to trigger the rupture on the Greendale fault in both directions and then more of a slip on a fault on the western end and a big cloud of seismicity at the eastern end near Rolleston is looking like it has "tweaked a few more pieces".
1:13pm - Journalists at the meeting are unable to see the presentation properly - which is being done on sheets of paper. Someone has climbed on a table to hold up the presentation - a member of the audience jokes, "technology in Christchurch!".
Mr Berryman continues to point out the major earthquakes that have affected Christchurch including February and June - he says his forecast model for future earthquakes are specific to the whole region rather than focussed on the city. This is because the aftershocks seem to have migrated to the east over time.
He says his team had been predicting a 5 - 5.9 quake at about a 50/50 chance for the coming year - he says it is unfortunate that something slightly higher has been experienced.
Although GNS have not had the chance to reassess probabilities since the latest strong quakes - he says this usually increases the probability a little bit. He says he will put out those probabilities as soon as they have the numbers. However, he says the probability of a seven is very low - "it's not zero but it is very low".
13:16pm -He is now talking about tsunami possibilities and says the models have been worked for offshore ruptures last April. If a magnitude 7 occurred offshore a small tsunami of one to two metres could be expected. GNS offered advice through ECAN and the emergency operations centre about what to do in that situation.
This situation is no different now in terms of tsunami and people should not worry about this. Tsunamis in Christchurch largely come from South America with 12 hours warning.
13:20pm - Stephen Bannister is next to talk and he is concentrating on what has occurred since December 23.
He says the largest events were about 4km off New Brighton Pier. On January 2nd the primary sequence was at the northeastern end of the cluster.
Each individual earthquake can be analysed individually. The three largest occurred on a thrust fault with a steep dip towards the south-east. The three events probably did not occur on the same fault, they were probably on sub-parallel faults all with the same dip.
In the first few hours each events probably triggered the next event as stress was transferred between each fault.
13:23pm - Mr Bannister is now looking in detail at each individual major quake. He points out high vertical acceleration during the February quake, less so in the June 13 quake. June 13 had high horizontal acceleration at coastal areas but was lower in the central city. With the current events in December the accelerations were much lower in the central city but were still high in Heathcote Valley and New Brighton.
13:27pm - Mr Berryman takes over and starts to talk about the depth of the recent quake. They have occured at 8 to 10km depth. This is the "very old rock of New Zealand" and where most of the quakes have happened. NIWA and GNS are working together to discover what is happening at various depths. NIWA when offshore found an extension offshore of the February 22nd fault and this is newly discovered compared with what is now called the Kaiapoi fault. The current earthquakes are reaching up towards this new fault but are not there yet.
He points to faults in the North and says they are "locked up" but can break into a significant earthquake "once in a very, very long time". The work they are doing confirms that quakes in the Christchurch area are very rare events. "It is very much, wrong place, wrong time for the Christchurch city in the 21st century".
1:30pm - Mr Berryman now shows those gathered a depth profile - made using the same technology used for oil profiling.
Most of the quakes are occurring deep in the Greywacke rock area - which is "hundreds of millions of years old" and forms most of the underlying base of New Zealand. Movement on the Christchurch fault lines has occurred over millions of years as compared to say thousands of years on the Alpine fault line.
Recent quakes have come up to about a kilometre below the surface such as the Kaiapoi fault. There is little movement or disruption here on his diagram, which he says shows the quake is a very rare event.
In the deeper older rock there is more disturbance. This explains why a sequence of quakes occurs after a big quake - as stresses are redistributed deep underground. Only the bigger earthquakes rupture higher.
The point Mr Berryman is trying to make is that recent events are very rare.
13:35pm - Berryman says the expectation is for a decay period for quakes over the next time period - like experienced after the February quake. He says there is "almost certainly" a five out there, plenty of fours and threes on a "daily basis".
Post-September GNS thought after the big quake the decay period would occur and then completely die away. However, now they now there is the possibility of rejuvenation, but a further big will not re-rupture the faultlines that have already had their big earthquakes. The feeling is that a lot of those have been concentrated on the city so further large earthquake activity is likely to be further away than the city.
13:40pm - Mr Berryman says the disturbances from the Darfield quake may have created a disturbance that might last about thirty years. But the quakes from this disturbance will move around - the city may have had the worst of this but Canterbury as a region could experience quakes from this for the "next few decades". This would not necessarily mean people would be worried by these or not able to get on with their lives. Physical damage may be very minimal and the mental damage of continuing shakes may be stronger.
In comparison to Wellington, Mr Berryman says Canterbury seismic activity is currently much higher. Previous to the recent quakes though the seismic activity in the two areas was actually quite similar.
He says future activity at a moderate level further away from the city "does not inhibit the reconstruction moving forward".He says the recent events have not been a significant insurance event.
13:42pm - Mr Berryman says it looks like we have "filled up" the expected amount of after shocks. He says this is good news. This issue is rather complex but as far as I can understand Mr Berryman seems to be saying that until the recent quakes Christchurch had fallen behind the expect level of aftershock activity expected since the September quake. That is there was some "missing energy" (as Bob Parker calls it), that has now been accounted for following these strong Christmas/New Years shakes. Mr Parker and Mr Berryman agree this is good news. He shows a graph which shows the actual aftershock activity line now converging on the expected number.
This means it is quite probable that quakes will gradually decline. This doesn't mean the quakes will stop, he can guarantee fives in the coming months but hopes they will be mainly offshore. He does not think they will be damaging.
The meeting has broken for questions video of this will be available online shortly.
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6/01/2012 2:55:52 p.m.
No luck watching it on my laptop, PC or IPad (needs Flash which can't be downloaded onto an Ipad I believe. I will wait and watch the video later. I am guessing there are settings somewhere on my PC and Laptop that are preventing it playing - no fault of TV3. And to Jay above - the likes of you make me ashamed to be a cantabrian.
6/01/2012 2:49:09 p.m.
thanks tv3 it worked fine for me on google chrome. maybe the others should get better computers :)
6/01/2012 2:45:50 p.m.
I watched the whole session with few problems.
Once again Bob Parker showed why he deserves to be the mayor of Christchurch. Easy to understand , excellent in summarising questions and answers and a good organiser.
6/01/2012 2:35:27 p.m.
I could not get it to load and kept getting an error on google chrome but then tried it in Internet explorer and it work, It was well worth the watch..
6/01/2012 1:57:45 p.m.
I think TV3 is doing pretty good with the updates since the video thingee has overloaded - keep it up - I just keep refreshing.
6/01/2012 1:46:29 p.m.
Auckland guy wrote:
Well thanks TV3, I'm doing something wrong because the streaming is working fine for me- Firefox v9. Jay, you have my sympathies, clearly a piece of brick landed on you during the last earthquake and knocked out all the common sense, and instead replaced it with irrational, illogical fear. You also forgot to include Ken Ring conspiracy and the reptilian overlords.
6/01/2012 1:40:27 p.m.
Eastern Anna wrote:
This is a very popular event! We all want to know whats going on! Heres what they say at the top of this page!
"Our live stream is currently experiencing very high traffic. If you are unable to watch please continue to refresh your screen. We will also have the full meeting up as a video later today."
Hurry up and wait - like we have been doing since Sept 10.
6/01/2012 1:17:38 p.m.
Brigita, try a different browser. It didn't work for me in Firefox but Chrome does.
6/01/2012 1:15:39 p.m.
Typical that the link to watch the show doesn't work, eh? They're hiding stuff from us, there's stuff they don't want us to know! It's probably the flashy expensive lunch being laid on for them all, using EQC money, instead of fixing our busted driveway, house, roads, etc!
6/01/2012 1:10:49 p.m.
can't watch it either, would really like to know what is going on since we actually live in the eastern suburbs
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