mexico city

to all our DIY family out in D.F. I hope you and your are safe after the earthquake.

+1... 

They improved their building standards after the last big one there, but still plenty of buildings that can fall down and kill people.

The death toll from the 1985 quake was something like 10,000.  The ground conditions under Mexico City do not support tall buildings.

JR

Mexico City had several "pancakes" which at first glance seem too-too similar to the one in ChristChurch a few years back. Aside  from older less strict building standards, the one in CC had political pressure over-ride the prime inspector's structural judgement; that could happen in Mexico also.

Both cities are old fill which was fine for the first small isolated houses but is a very bad base for tall buildings in an earthquake.

PRR said:

Both cities are old fill which was fine for the first small isolated houses but is a very bad base for tall buildings in an earthquake.

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Yup I think mexico city is built on top of a filled in old lake bed,,, The earthquake was some distance away but something like 4 or 5 stories high buildings resonated with the ground shaking repetition rate . I do not know if higher (more massive) buildings would be safer or not, perhaps(?). 

Agreed, I wouldn't expect rigorous enforcement of building codes (or anything else)  in mexico.

JR

JohnRoberts said:

but something like 4 or 5 stories high buildings resonated with the ground shaking repetition rate .

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The physics of this reminds me of those vibrating reed frequency meters, found on old generators to set the speed governor to 50/60 Hz. The fundamental input frequency hits the resonant frequency of a certain reed to shake it violently as an indicator. The other reeds are tuned slightly different, and hardly shake at all.

A reed meter:

http://www.antiqueradios.com/forums/viewtopic.php?f=8&t=229871

Also, Ella Fitzgerald singing just the right note to shatter a resonant wine glass.

Gene

The owner of the Mexican restaurant I eat at a lot is from Puebla which looks like the epicenter. Luckily her family is okay.