Liquefaction from the Sendai earthquake – a remarkable video | Hacker News Reader

Liquefaction from the Sendai earthquake – a remarkable video

blogs.agu.org

155 pointselliottcarlson29 comments

Even more startling is the liquefaction happening in Christchurch:

http://www.youtube.com/watch?v=2WoKu5VxKgs

Here is an awesome video by a Christchurcher showing how the sediments pouring up through earthquake cracks have the perfect mixture of water and soil to be prone to liquefaction:

http://www.youtube.com/watch?v=1KqlAMWMjOE

I spent a week clearing this crap out of people back yards with the student army of volunteers. They estimate 200000 tonnes of the silt had to be cleared.

Here's an example of the silt coming out of the ground minutes after the quake. http://www.youtube.com/watch?v=e_twYpUJl9o

And here's a good explanation http://mandenomusings.wordpress.com/2011/03/03/christchurch-...

For those of us who are not familiar with the term liquefaction. In simple terms, I think it means the soil becomes like quick sand because of the earthquake.

http://en.wikipedia.org/wiki/Earthquake_liquefaction

Exactly. Liquefaction is not water coming up from the ground, although that's a side effect of it.

That's the most casual walk through a Japanese park during an earthquake I can imagine.

That is really disturbing, and it reminds me of something I just read the other day.

For any Seattle startup folks, just remember that all of Pioneer Square (and then some...) is a liquefaction zone[1]. Also, don't forget that the Viaduct is a death trap, and you really are better off never setting foot (or wheel, I guess) on it.

[1] http://www.thestranger.com/slog/archives/2011/03/16/more-sea...

> For any Seattle startup folks, just remember that all of Pioneer Square (and then some...) is a liquefaction zone

For that matter, so is a large chunk of the Bay Area.

Whether it's earthquakes, wildfires, bizzards, tornados, hurricanes, etc there is always gouing to be something pretty much wherever you settle.

> For that matter, so is a large chunk of the Bay Area.

More specific?

Anywhere that's reclaimed infill: The Marina, most of Foster City, Treasure Island, parts of Fremont, etc.

Large areas south of market.

liquefaction hazards for SF: http://gmw.consrv.ca.gov/SHMP/download/pdf/ozn_sf.pdf other PDFs: http://gmw.consrv.ca.gov/SHMP/html/pdf_maps_no.html

I found it mildly interesting how the liquifaction areas are colored in a pleasant tone of green.

You should also stay in an underground bunker and never go outside, because dude do you have any idea how many asteroids are out there?? The entire surface of the Earth is an Asteroid Impact Zone!

or just stay off the viaduct. that seems far more straightforward :)

Yeah, avoiding the viaduct has always struck me as a sensible precaution.

The 520 bridge is also very vulnerable to earthquakes (the primary reason why it's being replaced).

You mean that bridge that's about a foot above the water level and, when there's a really turbulent storm, can have rough water on one side and calm water on the other, and have waves literally crashing over the cars from the one side of the water?

Nooo, I would have never thought that bridge would be dangerous in an earthquake! </sarcasm>

I'm not intending to mock you, though it's probably coming off that way. Outside of the cool special effects during a storm (seriously, the 'rough water, bridge, calm water' effect is quite eerie), I have no idea why that bridge was built the way it was.

It's about the same with the I-90 bridge too, and you don't even need a storm to see the cool effect of wavy water on the south side and calm on the north side. It always fascinates me when I drive over it. I've only had a spray of water hit my car once so far, I'll make a note to avoid either bridge during an earthquake. ;)

It's actually the non-floating parts of the 520 bridge that are the most vulnerable to an Earthquake.

Quite a remarkable video... a little less so when you get to the end and he informs you of the history of Tokyo Central Park (reclaimed land). Still... unbelievable. Much less dramatic that the Google images of entire communities washed from the Earth... devastating.

I've been in Tokyo for more than 20 years but I cannot tell which 'Central Park' this is.

Shinjuku Central Park is a well known one and it is surrounded by skyscrapers, but this one doesn't have them.

Any hints?

he says it is in reclaimed part of tokyo bay. so wouldn't have skyscrapers ALL around, but should have some in a few of the shots.

Ah I didn't notice it as I turned audio off.

Now I managed to spot it. The park is actually Makuhari Kaihin Park (幕張海浜公園) in Chiba, not in Tokyo (that's why I was not aware of it).

And yes it is on reclaimed land, the homepage of the park in fact mentions liquefaction.

I think it might be near Odaiba.

I've never experienced an earthquake. As such, the cracks and drifting earth make me doubt the reality of such a video. Does this drifting actually occur at the surface like that? Edit: speeling ;-)

I've been in 2 about 20 years ago; both ~5.1. If memory serves there were 2 distict types of shaking. The first was a fairly high frequency vibration that shook the walls and mimic what you see in movies; $#@! flying off shelves, etc.

The second came a few seconds later, and was a slow back and forth horizontal movement of the ground. I remember it being a bit faster frequency than that video shows, maybe about 1Hz, but it seemed like the ground was just moving fairly slowly back and forth a few inches.

I've heard many accounts of these phenomena from others. What I'm having difficulty with is the relative motion of the different pieces of earth. I live on pretty solid ground away from active fault lines. If one of our minor fault lines ever acted up, I could certainly imagine the kind of motion you mention. But if my property "cracked," I'd expect to feel the swaying motion and that each piece of my yard would move in the same direction preventing me seeing the motion. On further consideration that the park in the video is built on a former bay, I supposed the quake could be making the dirt float around on the mushy underside.

The first thing I noticed was an oddness about the crack in the sidewalk. It seems to have cracked perfectly along some crack line that's outside of the sidewalk (not likely - just because dirt cracks underneath doesn't mean the concrete will crack exactly where the dirt does) and there seems to be some rubbery surface where the crack ends in the sidewalk (it stretches as the parts of earth move in different directions.) Not like the pure concrete sidewalks I'm accustomed to, but Tokyo is worlds away and maybe it's not just concrete.

P.S. Why the downvoting on my original post? Is it not a valid question?

That pavement is most likely asphaltic concrete (commonly, though incorrectly, known as "asphalt"), which is a mixture of asphalt and sand/gravel aggregate. It's fairly flexible, at least compared to Portland cement concrete.

I was in the earthquake in Tokyo (a few kilometers from Odaiba where that video was likely taken) and I can say I believe it. Out this far from the epicenter it felt very wobbly. It was like my house was on a block of Jell-o. It felt like a 1-3 htz wave. There was a good three minutes of very strong movement and another severe aftershock a 10-20 minutes afterward.

BTW, The girl having a picnic with her boyfriend when the video starts is shouting こわい (kowai) which means "scary!".

"a sombrero, and a huge clock"

Is this Chuck Norris wielding the camera?

Reply on news.ycombinator.com