Thousands of tons of bombs were dropped on Japan in WW2. Many of them didn't explode. This airport was apparently an active airfield at the time the US was bombing Japan and 500lb bombs were the sort of thing used to destroy parked planes.

Yes, someone could have snuck into an airport and buried a bomb underneath the runway, then cleaned up the digging operation so as to not be noticed, but horses, not zebras.

They're just asking on what basis the article is confident that it's a specific bomb from a specific era. Is it based on a forensic analysis of the shrapnel, something like that? If it's just an assumption based on the context, you'd want to say "an explosion, believed to have been caused by an unexploded WWII-era bomb...".

In how many eras were bombs being dropped on this airport?

An explosion goes off under a runway. The article says "it's a bomb, it was dropped on the runway 80 years ago, buried with dirt, paved over, then it went off".

Cool. Now, how did you figure that out? Did someone analyze the shrapnel and conclusively date it to allied bombing campaigns in WWII, or is that what a source close to the events said, or did the reporter just... look at the picture and shoot from the hip? Any of these is an acceptable answer, so long as readers know which one it is.

If it wasn't from the war, then the more likely scenario is the bomb feel off a plane after the war than somebody snuck into the airfield. Bombs do fall off planes.

My question was more of, how do they determine this sort of thing or is it just an assumption because it is the most likely scenario?

You’re assuming the bombs like this were removed after the war. They weren’t. No one knew they were there.

We are still finding unexploded artillery shells from the first world war in France. Germans are still finding bombs in cities.

The chemicals in the fuses mix and become unstable over time. The explosives don’t degrade as much.

If you wanted further verification, the bomb casing leaves fragments and explosives leave residue.

I'm not doing anything of the sort. I know bombs are still there from WW2. Just because there are still bombs from WW2 does not mean that every bomb that goes off is from WW2. While it is likely that the bomb is from the war, I haven't seen what evidence they have confirming that. That is all I am asking for.

The evidence is likely simple deduction, as in asking "when was the last time this area was bombed" combined with the history of the airport (built for the military in 1943, later converted to civilian use) and also noting other unexploded bombs have been unearthed in the area.

For it NOT to be a WW2 bomb would mean somebody sneaking in another bomb and paving it under the runway without being noticed.

Yes, and it results in a huge amount of paperwork. You can't just randomly show up at your destination missing a bomb - especially during peacetime. They'll be combing over every part of your flight path to find it.

It could've also been intentionally buried there by bored soldiers, or placed there by airport maintenance people as a prank, or ended up there due to a freak teleporter accident. Maybe it was even put there by Godzilla. Maybe the Infinite Improbability Drive spontaneously materialized it, together with a bowl of petunias.

If you find a bomb in an area which is known to have been bombed, without any evidence to the contrary it is pretty safe to assume it's there due to the bombing.

Sorry about that. The article obviously doesn't explain. Here's my thoughts on it.

I don't think they did any exhaustive research. They didn't have to.

You would be able to look at the crater and see sizable pieces of a military air-dropped bomb. Normal bombs don't disintegrate. If they send it to a lab they can tell what explosive was used in it, which will roughly tell you when it was manufactured. (Assuming they don't find a serial number.)

That by itself is hardly conclusive, but that completely changes when you find identical unexploded bombs buried in the same area.

It would be rather odd if somebody came along later and put the same kind of bomb used in WWII in the ground. When the bomb got there isn't that important.

Likely because no one's dropped bombs on Japan since then

That absolutely can be a WWII bomb. They are still finding unexploded artillery shells from the first world war in France!

Let me repeat that, hundred-year-old shells are still underground, intact, and the explosives in them are just as powerful as when they were manufactured.

Chemicals in fuse can slowly combine until they detonate.

The odds of someone planting more explosives in a field potentially containing a dozen WWII bombs from multiple attacks are remote.

Usually shrapnel, working out the depth at which it exploded, the nature of the explosion (recorded on video), and historical evidence of bombing.

There is a buch of forensic methods around this.

I understand that is what is usually used, but I was asking for the actual details which was scanty in the article. Is this what they did or are they still looking into the forensics?

Forensics identified a valid digital certificate matching ww2.co.jp. The issuing CA is currently denying responsibility.

It's pretty easy to identify from the shrapnel.

I understand that it is easy, but is this what they did? That was my whole question and nobody is actually answering my question

Because it's a silly question. The airport was bombed in WWII by the US, just like the rest of the country, and Japan wasn't in any war since then, nor was it in any war before then when it would have had such bombs dropped on this location (there was a naval war with Russia in the 1900s, but that didn't result in bombs dropped on Japan).

So basically you're asking for forensic evidence to prove that this bomb wasn't the result of time-travelers or teleporters or something equally fantastical. It's a ridiculous question. Of course it's an unexploded WWII bomb, what the hell else would it be?

Planting a bomb especially of that size (needing a vehicle and multiple men to move) in the ground under a paved taxiway at a major airport without anyone noticing? Not very likely.

The WWII explanation is much more plausible. It happens at Schiphol too that they find them (luckily not by them exploding randomly but usually during construction efforts)