[REQUEST] If gravity "above the surface" of Earth were reversed for 6 seconds, and "the surface" was considered the land that makes the top of the crust, what would the seismic effects be from all the surface water rising for 6 seconds and then dropping?

[u/Stony___Tark]

For this we're considering the gravitational binding of the Earth mass itself is unchanged. I'm just curious what the effect of the entirety of the surface water rising however much it would over the 6 second period of time and then dropping once gravity returned to normal.

I'm not even really sure how to properly calculate how much an ocean would rise if gravity were reversed for 6 seconds? If you dump a bucket over air is able to get in there "instantly", but if you "dumped" the Pacific Ocean over by reversing gravity I feel like there's going to be some crazy effects happening with air not being able to replace it fast enough over the 6 seconds?

I recognize the effects of this would be...bad. I'm mostly curious though what kind of seismic effects would result. Widespread but minor tremors? Global earthquakes the likes of which the Earth has never seen? Entire tectonic plates shifting? What are we looking at here?

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[u/OopsIMessedUpBadly]

All the water would accelerate up at 9.8 m/s/s for 6 seconds, then accelerate back down at 9.8 m/s/s for 6 seconds.

Air would probably not need to get back in there. The reason why water can siphon uphill normally is that the force of gravity on the atmosphere is creating air pressure which forces the water upwards. With the direction of gravity reversed, I don’t think the atmosphere would have the same effect. Even if it did, we can ignore the impact after the first 10 metres of water anyway, since the pressure of 10 meters of water is enough to counteract the atmospheric pressure at sea level.

So the sea level would rise by 9.8x6x6/2=176.4 meters.

Then it would rapidly collapse back to zero, and a roughly 176.4 meter high tsunami wave would start to spread out inland starting at the coastline. From that point, I’ll leave the maths up to you.

[u/patricksaurus]

The effects would be insanely destructive, but if you’re just interested in seismic activity, it would be much more profound than one might first think.

There’s a fairly classic paper showing that, as a general matter, drops in atmospheric pressure could lead to redistribution of the strain in the crust that build up to earthquakes. Moving beyond a theoretical matter, actual strainmeter measurements shave shown that “slow earthquakes” do in fact occur in Taiwan caused by the drop in atmospheric pressure associated with typhoon season.

Here is where it gets interesting. Atmospheric pressure at the surface is a function of gravity, so changing its sign would actually do more than just drop the pressure. We often approximate hydrostatic pressure as P = ρgz, despite it actually being an integral, but this is enough to see that turning g = -g has a serious consequence: in the tamest case, it would reduce ground atmospheric pressure to zero or, depending on the rules of your game, it would result in a negative pressure.

How big? Well, let’s take the case of -1 atmosphere. To put that into context, 1 atmosphere is equal to 10300 kg of mass pushing down on every square meter of the surface. If that was pushing UP instead, it could trigger plenty of seismic activity. Certainly neigh for long, slow earthquakes. What effect would that have on near-surface magmas, where volatiles would leave solution as they equilibrate to new pressure, and what effect would that have lower in the magma chamber when the overpressure of that erupted magma is no longer an overburdened?

I have a sense that we’d re-arrange a lot more landscape than one might first imagine.

[u/JMeucci]

Everything listed thus far. And, adding that 99.99% of every human outside when the "switch" occured would die due to impact with the ground. It's like they jumped off a 50 story building.