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Endorkend OP t1_j7pqys6 wrote

Reply to comment by CrustalTrudger in What would happen to a person standing on the edge of a faultline when it moves? by Endorkend

So the shockwaves will almost purely go through earth then?

I've seen footage of volcanoes blowing where there is a visual airborne shockwave.

I guess it's because fault line movements are inside the earth and involve movement of obscene distances it gets spread better, but I thought that with the stupendous amount of energy released it would still have a decent effect above land too.

Thanks!

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CrustalTrudger t1_j7pye07 wrote

The interaction of seismic waves and the surface of the Earth can produce measurable pressure waves in the atmosphere (e.g., Donn & Posmentier, 1964), but generally nothing that's going to be damaging. This of course depends on what the fluid in contact with the solid earth surface is though as a tsunami effectively represents a displacement wave from surface deformation (from actual vertical change in the ocean bottom as opposed to seismic waves specifically), but here, it's not the pressure wave that's dangerous per se, but the resulting inundation when this approaches shore.

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Sub0ptimalPrime t1_j7qaru9 wrote

It's also important to note that the energy epicenter is below ground. So the release of energy (the equivalent of the volcanic "explosion" you speak of) is actually below ground at the point of greatest elastic rebound (or friction overcome). That "explosion" has to then travel through thousands of feet of rock (depending on how deep the epicenter is, which is controlled by what kind of plate margin it is), so it is greatly dissipated.

Edit: has to travel through *miles of rock ("thousands of feet of rock" wasn't wrong, but doesn't put the reader in the right frame of magnitude)

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GaudExMachina t1_j7qx8ut wrote

To piggyback, I checked around and seismologists suggest this was at a depth of 18 km below the surface. Not as deep as some, so more surface effects.

Also a horizontal strike slip, so lateral movement between the two plates, so there won't be much vertical component. 7.8 is a massive earthquake, but by no means as insanely powerful as some of the 9+ that have hit Chile within recorded history. I recall reading that one of those in the 1950s had an offset of 30 meters along its rupture zone (deep in the earth), but I'd need to go find a source on that.

For an exceptionally rough estimate, OP could try envisioning the ground suddenly shifting laterally 15 meters while they stood upon it, then scale that back by a factor of more than 10 as this one was considerably less powerful.

Devastating for a building that rises multiple stories, while having a narrow base and made out of inflexible materials. But for a person on the surface of the earth, it would knock them flat.

Edit: Good illustration posted in pics
https://www.reddit.com/r/pics/comments/10wsr6n/anatolian_plate_moved_335_meters_after_the/

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