Nick you ok?

[kiwigeo]

Christchurch hit by a swarm of aftershocks today.....just reading about it now. Hope youre ok mate.

[Nick]

Bloody things! A 5.8 then a 5.3 then a 6 (not to mention the subsequent tremors/aftershocks clustered close to the bigger ones) all within two hours and all around 8k's deep! Could really do without this crap at this time of year. Everybodies Ok this time and there have been a few buildings fall over but fortunately they were due for demolition so nobody in or near them. I'd been out at the airport picking up my partner's daughter who lives in the North Island, she was asking all about the february quakes & what we had been through on the way back from the airport. Bugger me if we hadn't been back home less than an hour & the first one hit so she now knows what it feels like. Bit of a scary way to find out though!
These were centred 10 k off the New Brighton coast, not sure if it's part of the port hills fault line or whether the February quake has stressed this fault? I know Jarg said there was another fault line out there.

[kiwigeo]

Nick,

Looks like an intial quake on eastern end of the Port Hills Fault which then triggered quakes on at least two other faults. The fact one of the later shocks was bigger than initial shock suggests that early shock(s) may have affected local stress field which was relieved by some of the subsequent shocks.

[Sean Syman]

Good to hear you're all good Nick, I'm back in Wellington but really understand what you're going through again. Sounds pretty similar to the ones we had in June from what I can tell, it's the aftershocks that cause heaps of the stress. Keep strong man, and Merry Christmas!

[Kim]

Geez Nick, your whole community must feel under siege. I can't even begin to think what the good people of Christchurch are going through, and right before the festive too...Must be making folks there pretty short and feeling they've had more than their fair share of this crap, and nobody could argue with them...

My Xmas wish is reserved for Christchurch this year hoping that this latest rumble was the one to finally clear the belly and allowed all this to become a distant bad memory.

Best wishes to you and the rest of your gutsy mates in CC.

Kim

[Kamusur]

Jeez the people need a break already from this sh?? It doesn't deserve to happen anymore.
Take care and God bless them all Nick.

Steve

P.S. Please a Merry Christmas for everyone over there.

[Dennis Leahy]

To Nick and everyone in and around Christchurch:
Very glad to hear that the buildings that came down were slated for demolition and that no one was in or near them. You're in my thoughts.

To Mother Earth:
OK, that's more than enough, thanks. Move along now.

Dennis

[kiwigeo]

Good to hear you're all good Nick, I'm back in Wellington but really understand what you're going through again. Sounds pretty similar to the ones we had in June from what I can tell, it's the aftershocks that cause heaps of the stress. Keep strong man, and Merry Christmas!

Interesting things happening out in Pegasus Bay. Looking to me like we have the following scenario:

1. initial shake on eastern end of Port Hills Fault.
2. activation of at least two north-south trending thrust faults that are probably one of a spider web network of secondary faults that join up the major E-W trending strike slip faults. if you look at mapping of faults further north based on offshore seismic shot by various oil companies over the years you can see similar systems of E-W major faults and numerous secondary faults linking them.
3. The fact the new faults are thrust faults presents the scenario of a tsunami. This said I think the risk is very low. To trigger a tsunami you need a substantial vertical movement of ocean floor and at least a mag 7 quake.

The above are my opinions only based on a very limited data set.

Cheers Martin

[Nick]

Thanks Steve & everybody for your thoughts, nice to know we are being thought of & yes Kim, it's starting to wear thin now, almost 18 months of these bloody things & the insurance companies won't do anything until they feel we have finished getting shakes so any repairs to houses will have been set back even more with this bloody lot! Thanks Dennis, hopefully Mother Earth is listening to you because she sure aint listening to us!
I also feel really sorry for the people near the coast/beaches, seems they've been hit with yet more liquefaction, that's five times now they've had to dig several inches of silt from in or around their houses. Fortunately where we are is still close to the beach but has thus far been immune to large amounts of this bloody stuff!

I think your scenario is what the boffins here are thinking too Martin & it would seem the most logical, they were all thrust type quakes (bloody floor littered with stuff again!) & Jarg & his team had identified that there were several north south faults off the coast running perpendicular to the Port Hills fault so either the earlier quakes along the hills fault had wound these up to the point that they couldn't hold anymore or as you say the first shake was centred at the eastern end of the hills fault giving the north south stuff a poke in the ribs , which would explain the larger magnitude shake after the initial one because the pattern up until now has been very much one of an aftershock within an hour of the initial shake in the same range of magnitude but lesser than the first then diminishing shocks from there.
Hey Sean, hope having to work for a living isn't too onerous! Campus shut down again but probably open again before the end of the month, they're getting the hang of doing these inspection things now!

[kiwigeo]

Nick if you check out some of the papers written back in the 80's (Jarg and Mark Yetton co-authored some of them) that looked at seismic risk in the Chch area there are a couple of fault systems north of Kaikoura that consist of E-W trending strike slip faults connected by a spiderweb of secondary (most likely thrust dominant) faults. These fault systems are a manifestation of the regional tectonic regime (transition from subduction to transcurrent plate boundary through Marlborough-Nth Canterbury).....it's logical that the fault systems developing under and around Chch should be a continuation of this process...the only complicating factor is the presence of Banks Peninsula volcanics.