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Following on from Destruction by design - how best to go about crafting a ruined landscape? I'm asking questions about the signature destructive patterns of different weapons systems. This is the third, the first follow up deals with deliberate demolition type destructive processes and can be found here and the second here deals with orbital energy weapons.

This question is about the differences, if any, between the patterns of destruction caused by precision kinetic weapons, (those scaled to destroy buildings rather than whole cities), versus large conventional weapons like the grand slam and other massive bombs that detonate below the ground surface. Basically how different would a city ruined by orbital bombardment look to one devastated by seismic bombs?

Good answers will consider the initial effects of the bombing/bombardment but also the differences, if any, in the way such a devastated landscape ages as vegetation returns and weather takes it toll.

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  • $\begingroup$ Are these orbital kinetic weapons (Rods from the Gods) or hyper velocity projectiles like the US Navy is developing? $\endgroup$ – Green Nov 6 '17 at 12:49
  • $\begingroup$ @Green They're essentially the same, in terms of the magnitude of speed of impact, and thus the degree of penetration at a given size, the only difference might be with angle of impact. Given that I've specified a scale of impact damage the projectiles would have to be reasonably similar too. $\endgroup$ – Ash Nov 6 '17 at 12:58
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The big issues here are the amount of energy involved (kinetic or chemical) and the surface the weapon is dropped on. Another key factor would be the depth of detonation of chemical explosive. But the most important factor would be what else was known by the investigators.

If for example the investigators knew they were comparing a particular design of bomb with a particular velocity and mass of kinetic weapon, that would be a great help, but if this information was not available it would make telling the difference much harder.

As can be seen from this reference If the speed and mass of the kinetic weapon are variable and the mass, type and depth of detonation of conventional explosive are also variable one can be made to mimic the other fairly closely.

That said “It is recognised that some of the chemical energy of the explosive is partitioned to an expanding gas ball which is never present during impact cratering and there are other minor differences”. So it might be possible to tell, although it would probably be very difficult.

If the investigators knew or could reasonable infer that the same type of weapon had been used to make a large number of strikes in different types of terrain such as sandstone, clay, granite etc detailed ballistic / forensic techniques might reveal the cause of the damage.

Immediately after the impact it might also be possible to detect traces of explosives in the crater and for a long time after the presence of heavy elements such as iridium might indicate an asteroid fragment had been used. But these methods would not be fool proof due to the wide range of chemical explosives possible (not all relying on nitrogen) and the options of using alternative types of bombardment materials other than the “obvious” one.

So in summary: perhaps - but it’s a tough one.

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Energy is the key to this.

The energy required to destroy a building with a bomb is fundamentally the same as the energy required to destroy a building with an orbital strike. That's going to mean you remove the building and leave a crater of approximately the same size regardless of which approach you use. Same energy, same direction of impact (above), same damage.

The biggest difference on the ground will be the cleanup, you're not going to need bomb disposal teams.

The fires caused by bombing in WWII were the result of incendiary bombs rather than high explosives. Bombs specifically designed to start fires rather than cause explosive destruction. Modern bombs aren't designed that way and mostly just cause explosive damage.

On a related note:

Why are impact craters always round? Most incoming objects must strike at some angle from vertical, so why don't the majority of impact sites have elongated, teardrop shapes?

At the moment an asteroid collides with a planet, there is an explosive release of the asteroid's huge kinetic energy. The energy is very abruptly deposited at what amounts to a single point in the planet's crust. This sudden, focused release resembles more than anything else the detonation of an extremely powerful bomb. As in the case of a bomb explosion, the shape of the resulting crater is round: ejecta is thrown equally in all directions regardless of the direction from which the bomb may have arrived.

What this all adds up to is that your future archeologists may not be able to tell the difference between orbital bombardment craters and bomb craters.

I also found this*, which will take some reading, but may be of interest to you.

*Basics of Impact Cratering & Geological, Geophysical, Geochemical, Environmental Studies of Some Impact Craters of the Earth

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