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#217965 - 02/25/11 12:44 PM Re: New Zealand : 6.3 earthquake in Christchurch. [Re: scrounger]
Dagny Offline
Pooh-Bah

Registered: 11/25/08
Posts: 1918
Loc: Washington, DC

It's being reported that the degree of liquifaction in this 6.3 quake was orders of magnitude worse than in last fall's 7.1 quake. Must be crazy to see the water and silt seeping up through everything.

ETS members in quake country -- do you all know the liquifaction potential in the areas in which your homes and workplaces reside?

As I recall from news reports of the 1989 Loma Prieta quake, San Francisco's heavily damaged Marina District was known to be on land prone to liquifaction.


Video:
http://tvnz.co.nz/national-news/liquefaction-across-christchurch-2-23-video-4039338

http://www.nzherald.co.nz/natural-disasters/news/article.cfm?c_id=68&objectid=10708723

Christchurch earthquake: Levels of liquefaction 300 - 500 pc worse

By Hayden Donnell and Paul Harper

http://www.es.ucsc.edu/~es10/fieldtripEarthQ/Damage1.html

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#217967 - 02/25/11 01:42 PM Re: New Zealand : 6.3 earthquake in Christchurch. [Re: Dagny]
hikermor Offline
Geezer in Chief
Geezer

Registered: 08/26/06
Posts: 7705
Loc: southern Cal
Basically, if you are situated on deep, fine grained sediments or on land that has been created by filling in an estuary or bay (the Marina situation) you are susceptible to liquefaction.

I once worked at Liquefaction City, the Channel Islands National Park Visitor Center, which is situated right on the beach, on sediments that are thousands of feet deep. Seemed like a bad place for a visitor center; I found out that the building is built on deep pilings that presumably will counter the liquefaction. We will find out some day. In any event, our significant museum collections are not kept in the building, but are some distance away in a non-LQ situation.

I believe that in California the earthquake hazard maps display liquefaction zones, so the information is readily available.

I have vivid memories of surfacing after a hard day's scuba diving (work, not recreation), hoping to catch the World Series, and instead watching the Marina District burn...
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#217969 - 02/25/11 02:23 PM Re: New Zealand : 6.3 earthquake in Christchurch. [Re: scrounger]
Dagny Offline
Pooh-Bah

Registered: 11/25/08
Posts: 1918
Loc: Washington, DC
Article on how the Christchurch destruction is relevant to the U.S. west coast -- including Oregon's Willamette Valley.

http://www.sciencedaily.com/releases/2011/02/110222152504.htm

"The latest New Zealand earthquake hit an area that wasn't even known to have a fault prior to last September, it's one that had not moved in thousands of years," Yeats said. "But when you combine the shallow depth, proximity to a major city and soil characteristics, it was capable of immense damage.

"The same characteristics that caused such destruction and so many deaths in Christchurch are similar to those facing Portland, Seattle, parts of the Bay Area and many other West Coast cities and towns," Yeats said. "And it's worth keeping in mind that New Zealand has some of the most progressive building codes in the world.

They are better prepared for an earthquake like this than many U.S. cities would be."



NYC more vulnerable than previously thought?

http://www.independent.co.uk/news/world/...ne-2223545.html

"Cities like Christchurch, which are only known to lie on a fault once an earthquake occurs, are much harder to protect against. Recent seismological studies have suggested that major cities like New York and Beijing, which are situated far from tectonic plate boundaries, may in fact be more vulnerable than previously thought to seismic shifts."


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#217970 - 02/25/11 02:59 PM Re: New Zealand : 6.3 earthquake in Christchurch. [Re: scrounger]
Lono Offline
Old Hand

Registered: 10/19/06
Posts: 1013
Loc: Pacific NW, USA
Smarter emergency managers that I know are keeping track of the inventory of unreinforced masonry (URM) buildings in their areas, because in a local quake those will be the first to go down, and go down hard. And there are handy maps of our liquefaction prone areas, they are well known. The ChCh quake was shallow and lasted for ~45 seconds, an eternity for anyone there. When Seattle has its EQ, it will last upwards of 4 minutes. Liquefaction areas - much of downtown Seattle, some northern neighborhoods, the entire industrial area and harbor area of Harbor Island - will be turned to jello, impassable. Building codes are like opinions, everyone has them - and little of the built environment is built to the most recent code, usually it has been retrofitted to an earlier code. And even those codes were built for outdated EQ scenarios, such as 45 second temblors rather than 4 minute shakes.

People are funny this way - if the magnitude of an EQ event is too scary or too catastropic to deal with by a sane building code, they will actively work to define the problem in a way that they can deal with and mitigate. This is going on right now - Seattle wants to build the largest tunnel in the world (?) to replace the Alaskan Way Viaduct, which runs along the waterfront behind a seawall (which is also failing and in need of repair). Now, there's no doubt that the Viaduct needs to be replaced, the problem is that city fathers and planners have grand plans for the space that would be opened up by an underground tunnel; the real problem with a tunnel is it will be forced through an area extremely prone to liquefaction. Tunnel collapse, inundation with seawater, even tsunami are some of the risks. So they are going great lengths to re-define the threat scenario, including choosing a EQ that is not the most damaging possible, nor are they choosing the most likely shake scenario, which will go on for minutes, not seconds. And of course, not answer in a definitive way, what if Puget Sound experiences a tsunami? The curt answer is, if a tsunami hits we have other crises to deal with. Which begs the question, why a tunnel, when an above ground throughway can be constructed to replace the Viaduct, at much lower cost, and built to survive tsumanis and EQ damage. That's an inconvenient question, as long as so many have so much money invested in all the new found waterfront that building a tunnel could open up. In the end, you can ask the question, will the new tunnel survive? The answer is Yes, to the question asked for a ChCh style quake: if you ask the harder question, could this tunnel survive a 4 minute shallows Seattle Fault quake, the answer gets much sketchier.

Apparently the Seattle city fathers have decided in favor of drilling their tunnel, and when The Worst Happens someone else will have to deal with that. The law of averages says it won't be them anyway. I would be happy if they started by asking the right questions, and if they still came to this answer, then so be it. Never underestimate the power of denial...

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#217971 - 02/25/11 04:15 PM Re: New Zealand : 6.3 earthquake in Christchurch. [Re: scrounger]
Dagny Offline
Pooh-Bah

Registered: 11/25/08
Posts: 1918
Loc: Washington, DC

Tunnels are not my favorite thing, would be terrifying in an earthquake.

Waterfront real estate is extremely alluring to city planners.

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#217972 - 02/25/11 05:03 PM Re: New Zealand : 6.3 earthquake in Christchurch. [Re: Dagny]
Arney Offline
Pooh-Bah

Registered: 09/15/05
Posts: 2485
Loc: California
Originally Posted By: Dagny
Tunnels are not my favorite thing, would be terrifying in an earthquake.

When living in San Francisco, the thought of commuting everyday on the BART train that goes under the San Francisco Bay was always a frightening thought until I saw something on TV that mentioned that that particular tunnel was much safer than you would think.

I'm sure every underwater tunnel is different, but in this case, the expert mentioned that ground movement is generally less intense as you go down into the earth, compared to a thin, swaying skyscraper, so the tunnel would be subject to less shaking than above ground structures. Plus, being a tunnel, they are naturally quite robust in their construction.

Anyway, still a frightening thought, but it did make me feel better about it. (crossing fingers)

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#217996 - 02/25/11 11:24 PM Re: New Zealand : 6.3 earthquake in Christchurch. [Re: scrounger]
Art_in_FL Offline
Pooh-Bah

Registered: 09/01/07
Posts: 2432
I thought this was an interesting picture of the situation that puts it in a different context. From a distance you can see it is a wide area, downtown, and considering that the majority of that dust is a result of damage to buildings, catastrophic.

http://scienceblogs.com/catdynamics/2011/02/christchurch_moments_after_the.php

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#218299 - 03/03/11 06:07 AM Re: New Zealand : 6.3 earthquake in Christchurch. [Re: scrounger]
sealander Offline
Stranger

Registered: 09/20/10
Posts: 15
Loc: New Zealand
Hey y'all

I live in Christchurch, and life here hasn't been a lot of fun lately. But I have learned a few things about coping with a natural disaster. One of the things that don't seem to get mentioned much is the aftershocks. Since the magnitude 7.1 earthquake in September, we've had more than 4000 aftershocks. We were getting at least one magnitude 5 quake every month and they were still causing damage. The damage caused by the Feb 22nd quake last week actually stemmed from 3 shallow quakes within about 15 minutes. The ground acceleration was 2.2 G. The building code here is for 1.8 G at most. You can literally see the ground moving when you're outside - some of the aftershocks were violent enough to knock us off our feet.

Anyway, some things I have learned:
1. Storing 3 days supply of water is not enough. Even reserving it for drinking, we seemed to go through it faster than expected. Had to put the chickens on tight rations, before the water tanker got to our area.
2. If you're planning on using your hot water cylinder as a source of water in an emergency, make sure it can be drained even if the mains water supply is out. Our new cylinder was installed 3 days before the quake (old one got cracked in the September quake). It won't drain if there's no water going in to it. I assume that's to stop the heating element from burning out if the cylinder got drained while the element was still on. There's probably a way to drain it manually, but with the violence of the aftershocks no-one is going up in the roof space to find out.
3. As well as storing water, keep some clean empty bottles too. That way when a source of water is located, you've got something to put them in. Or you can give them to the friends and family who ignore all the constant public service messages about how to prepare for a disaster, and find themselves queuing at the water tanker with nothing but a dirty mop bucket.
4. And speaking of which, you can never have too many buckets. Make sure your collection includes one big enough for an adult to stand in - you can use that for washing yourself, clothes, the baby etc. Remember that if water isn't coming into your place, chances are you may also be having trouble getting rid of waste water. Our street is humped up outside and liquefaction has caused pipe damage so the sewer is backing up. So we're trying not to put much down the plughole. Have a few lidded buckets too, good for emergency toilets. A good big bowl is useful for washing dishes too.
5. Chances are the cellphone networks are going to be jammed within 5 minutes of a sudden disaster. That's what happened to us, text messages weren't going through, or took hours to get through and arrived out of order. One change I'm going to make is add contacts to an emergency notifications group on my phone so I can send one brief message to everyone as fast as possible. Cell phones did help save the lives of some people trapped in collapsed buildings. Something else I found out was that if the cell phone towers near you go out, your phone chews through a lot of battery power connecting to the next nearest tower. People's phone batteries ran down very fast.
6. Just because you have a car doesn't mean you're going anywhere in a hurry. Much of the city was completely gridlocked within 15 minutes of the quake.
7. Don't underestimate your emotional and mental response to a disaster. Frequent violent aftershocks which have been going on for months here, really make everyone anxious. I think the only other situation you could compare it to would be living in a war zone. The aftershocks can mean very little sleep for many days (they were coming every 15 minutes all night last week). This really does take a toll on your mental state, and your health. Your short term memory starts to go - we call it "earthquake brain" here when someone can't seem to focus on anything. Results in very poor driving smile

So I'm going to give us an 8/10 on disaster preparation this time around. 3 days supply of water - check, but should have stored more. Several months supply of food - check (got downright embarrassing when people keep trying to give us stuff - the only thing I ran out of was chocolate). Back up means of cooking and boiling water - check. But I should have done some trial runs with the thermette (volcano kettle). Campfire cooking takes some practice. Emergency toileting - gotta work on that one, having a backyard overlooked by the neighbours is not helpful. Solar camping shower - check, very useful, but nothing strong enough to hang it on in the bathroom, might put a heavy duty hook in there. Tent, so we could sleep on the lawn when the house was shaking - nope, still haven't got around to that one, thought it was overkill. Might rethink that one now wink

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#218304 - 03/03/11 09:14 AM Re: New Zealand : 6.3 earthquake in Christchurch. [Re: sealander]
hikermor Offline
Geezer in Chief
Geezer

Registered: 08/26/06
Posts: 7705
Loc: southern Cal
Very impressive and sobering first post. Thank you very much. Living in EQ country myself, I find your feedback extremely relevant and useful.

Best wishes...
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#218308 - 03/03/11 11:59 AM Re: New Zealand : 6.3 earthquake in Christchurch. [Re: sealander]
bacpacjac Offline
Carpal Tunnel

Registered: 05/05/07
Posts: 3601
Loc: Ontario, Canada
i'm glad you're ok sealander. great post. very insightful - thanks!
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