Mexico City earthquake

[southsider2k5]

Mexico City was just hit with somewhere between a 7.1 and 7.4 earthquake. Looks like some pretty serious damage from what is leaking out on to twitter at this point.

[StrangeSox]

Video from a high rise shortly after the quake:

 

https://twitter.com/dlprager/status/910213018566328320

 

I think Mexico is supposed to have pretty strong building codes, so hopefully the damage is minimized.

[Kyyle23]

wasnt there a really large earthquake off the coast of Mexico when the hurricanes were hitting a few weeks ago?

[StrangeSox]

wasnt there a really large earthquake off the coast of Mexico when the hurricanes were hitting a few weeks ago?

 

Yeah, down south in Oaxaca and also Guatamala. 100 people died.

 

http://www.cnn.com/2017/09/08/americas/ear...xico/index.html

Edited September 19, 2017 by StrangeSox

[LittleHurt05]

wasnt there a really large earthquake off the coast of Mexico when the hurricanes were hitting a few weeks ago?

 

Yup, it was an 8.1, almost 100 deaths.

[StrangeSox]

https://twitter.com/XEVATabasco/status/910223441877487618

 

video of a whole building just falling down after the quake

 

https://twitter.com/mcantu06/status/910221789619527680

 

explosions

Edited September 19, 2017 by StrangeSox

[Soxbadger]

https://twitter.com/XEVATabasco/status/910223441877487618

 

video of a whole building just falling down after the quake

 

https://twitter.com/mcantu06/status/910221789619527680

 

explosions

 

I cant speak (read) Spanish, but I believe in the comments people are saying that the first video is of a demolition not related to earthquake.

[StrangeSox]

I can read enough Spanish to get by. There are some people questioning and some journalists asking if the uploader shot the video and if they can have permission to use it, but nothing definitive. From the high rise video I posted earlier, you can see widespread damage so it's not inconceivable that someone managed to capture a building falling down.

[StrangeSox]

someone actually managed to catch the earthquake happening on video, look at that building sway

 

https://twitter.com/BreakWatcher/status/910222780968439808

 

 

[Soxbadger]

I can read enough Spanish to get by. There are some people questioning and some journalists asking if the uploader shot the video and if they can have permission to use it, but nothing definitive. From the high rise video I posted earlier, you can see widespread damage so it's not inconceivable that someone managed to capture a building falling down.

 

Its not inconceivable but when you look at the video the building isnt swaying at all (compare it to the other video you posted). When I first looked it just seemed the building fell strangely for an earthquake, but im not an expert.

Edited September 19, 2017 by Soxbadger

[Balta1701]

If anyone is interested in the early geologist's summary of this event I already have that put together and up here.

[Balta1701]

Its not inconceivable but when you look at the video the building isnt swaying at all (compare it to the other video you posted). When I first looked it just seemed the building fell strangely for an earthquake, but im not an expert.

Brick and mortar buildings will not sway. They literally cannot - you try to make brick and mortar sway and instead it fractures and turns to powder.

[Soxbadger]

Brick and mortar buildings will not sway. They literally cannot - you try to make brick and mortar sway and instead it fractures and turns to powder.

 

Bad phrasing on my part. I meant you dont see anything moving that would suggest an earthquake just hit.

 

Compare it to this one:

 

https://twitter.com/BreakWatcher

 

You see the building moving a bit and then just crumble on itself.

 

Im pretty sure the first one was an implosion.

[Balta1701]

Bad phrasing on my part. I meant you dont see anything moving that would suggest an earthquake just hit.

 

Compare it to this one:

 

https://twitter.com/BreakWatcher

 

You see the building moving a bit and then just crumble on itself.

 

Im pretty sure the first one was an implosion.

That is a very different type of construction. That is a "Soft story" building, with either a wood or concrete frame. Those are able to flex more, but it's often the case that they are weak during earthquakes because people like having open space on the first floor. Having too much open space on the first floor means that when the upper floors start moving, there isn't enough strength on the first floor to hold them in place, so the motion builds and they collapse from that.

 

Edit: Also don't know the quality of building code enforcement there. It's expensive to enforce building codes, so sometimes buildings like that aren't quite as strongly reinforced by steel as they should be. That often contributes to failure as well, but still very different mechanism of failure compared to brick and mortar.

[LittleHurt05]

Video from a high rise shortly after the quake:

 

https://twitter.com/dlprager/status/910213018566328320

 

I think Mexico is supposed to have pretty strong building codes, so hopefully the damage is minimized.

 

It was amazing when Santiago had like a 8.6 earthquake and there were maybe 7 deaths, because of their extra strict building codes.

[Soxbadger]

That is a very different type of construction. That is a "Soft story" building, with either a wood or concrete frame. Those are able to flex more, but it's often the case that they are weak during earthquakes because people like having open space on the first floor. Having too much open space on the first floor means that when the upper floors start moving, there isn't enough strength on the first floor to hold them in place, so the motion builds and they collapse from that.

 

Edit: Also don't know the quality of building code enforcement there. It's expensive to enforce building codes, so sometimes buildings like that aren't quite as strongly reinforced by steel as they should be. That often contributes to failure as well, but still very different mechanism of failure compared to brick and mortar.

 

Balta,

 

Yeah I dont know anything about construction. But when you look at the 2 videos, you notice in the first nothing (not trees, etc) are moving at all. You also will notice in the top right hand corner their is a flash which would suggest a controlled demolition.

 

Obviously hard to tell, but just trying to suggest not to believe everything on the internet.

[Balta1701]

It was amazing when Santiago had like a 8.6 earthquake and there were maybe 7 deaths, because of their extra strict building codes.

One of the other tricks is that the "moment magnitude" number does not translate to "intensity of shaking". You have to worry about the local geology and the distance/depth of the earthquake as well. When I'm writing a post on a major earthquake I've stopped leading with the magnitude number and I always immediately transition to a different scale - the Mercalli scale - which is a measurement of shaking at the surface.

 

Mexico City is a far worse geologic setting for earthquakes than Chile. In mountain ranges, rocks are folded and metamorphosed and seismic waves pass through pretty easily. Mexico city is sitting on lake sediments in a rift zone. Those type of sediments capture seismic energy and just sort of reverberate back and forth during an earthquake, increasing the damage.

[StrangeSox]

Balta,

 

Yeah I dont know anything about construction. But when you look at the 2 videos, you notice in the first nothing (not trees, etc) are moving at all. You also will notice in the top right hand corner their is a flash which would suggest a controlled demolition.

 

Obviously hard to tell, but just trying to suggest not to believe everything on the internet.

 

Here's another building collapsing in a similar manner

 

https://twitter.com/mark_tarello/status/910239593555021825

 

Would have been weakened by the quake, and then if it's a brick/block construction, failure would be very rapid compared to steel or reinforced concrete.

 

The flash in the first building could have been solar flare or an electrical short as things ripped apart. It'd be a weird place to put a charge (why would you need to weaken the top of the building?) and you only see one.

[StrangeSox]

One of the other tricks is that the "moment magnitude" number does not translate to "intensity of shaking". You have to worry about the local geology and the distance/depth of the earthquake as well. When I'm writing a post on a major earthquake I've stopped leading with the magnitude number and I always immediately transition to a different scale - the Mercalli scale - which is a measurement of shaking at the surface.

 

Mexico City is a far worse geologic setting for earthquakes than Chile. In mountain ranges, rocks are folded and metamorphosed and seismic waves pass through pretty easily. Mexico city is sitting on lake sediments in a rift zone. Those type of sediments capture seismic energy and just sort of reverberate back and forth during an earthquake, increasing the damage.

 

Maybe it's too early to have any idea, but is this quake related to the one from a couple of weeks ago at all?

[Balta1701]

Balta,

 

Yeah I dont know anything about construction. But when you look at the 2 videos, you notice in the first nothing (not trees, etc) are moving at all. You also will notice in the top right hand corner their is a flash which would suggest a controlled demolition.

 

Obviously hard to tell, but just trying to suggest not to believe everything on the internet.

That flash comes out of a 3rd story window, or just below it. You don't put demolition materials on the 3rd floor of a blowing building like that, at least not a small brick one that would just come down if you removed the supports - you'll scatter debris from that part of the blast everywhere. I think that's either an electrical short or a window blowing out.

[Balta1701]

Maybe it's too early to have any idea, but is this quake related to the one from a couple of weeks ago at all?

See the post linked above? There's a paragraph in there already.

[LittleHurt05]

Not looking good, buildings collapsing, at least 50 dead.

[Balta1701]

Not looking good, buildings collapsing, at least 50 dead.

The USGS has an automated system called "PAGER" that automatically assesses probability estimates of casualties around the world based on local geology, population density, building codes, and distance to a quake. It puts the highest probability of casualty numbers for this quake in the range 100-1000, and there's a 40% chance of >1000 dead. Similarly, most likely damage is $100 million-$1 billion, with about 40% chance of $1-10 billion.