Inspired by this news:
And this old thread about a Cecil column:
https://boards.straightdope.com/sdmb/showthread.php?t=41311&highlight=jump+chinese+china
My question is, how big an earthquake could be caused by the entire population of China jumping for joy?
The link to the column in that old post is broken. Here is the column link (courtesy of Randal Monroe.) (And isn’t that illustration pretty racist by today’s standards?)
Keep in mind that Mexico City is built on a swamp which is why the earthquakes there can have erratic and unpredictable destructive power. One building falls over the one beside it doesn’t, due to where waves in the soft ground reinforce each other.
My wild-ass guess is that the consequences of “many people jumping at once” carries a lot further on soft ground, so local seismographs will pick that up. Less likely to happen in a place with firm ground. I’ve been in places where a big truck going over a bump a few hundred feet away can be felt, because the soil is soft clay…
Soft materials are much more dissipative than hard ones. Jump on a steel beam, and you’ll make the ends shake. Jump in mud, and you’ll just splash.
Assuming you mean the entire population of China jumping where they stand at the moment, nothing. 1.3 billion people’s jumping, dispersed over an area as wide as where they reside, is nothing.
You’d have to have 1.3 billion people jumping in a fairly small and concentrated area for there to be anything significant.
I’m not a seismologist, but I live in Southern California so do know that earthquakes have different effects depending on the medium. For example, sandy soil can “liquefy.”
I know that not all the people in China liven one place and likely the soil types vary widely across its territory (or not?) but I still think there’s an answer possible.
I’m not a seismologist nor geologist, but in my understanding an earthquake happens because you have two uneven surfaces pushing up against one another. Since they’re uneven, they will sometimes get caught on a pair of bumps (or a bump in a dip) and so movement stops for a while. But while stopped, pressure builds behind the plates and eventually they snap free of the lock and there’s a violent movement.
In theory, this should mean that there could be a moment where the lock is just a hairs breadth from breaking and just about anything could cause it to go.
So, if the conditions were just right, having everyone in the country could well be the straw that broke the camel’s back.
Though, by the same standard, a butterfly coming to rest on a blade of grass could also be the final straw, depending on just how close the catch is to snapping.
Of the two, though, clearly the case where everyone jumps would be the one that is far more likely to trigger the release. Though, also clearly, the mass of a few billion people is well swamped out by the mass of a continental plate and is unlikely to prove a triggering event in nearly every situation ever.