I read years ago in a book ending (can't remember which book) that the scuttled German fleet in Scapa Flow is a good source of radiation free metal for making scientific instruments. Apparently the vast amounts of air required, that's now contaminated by those early detonations, to smelt iron ore leaves the metal contaminated and unsuitable for delicate measuring instruments to be manufactured from.
The effect on the earth's structure and surface is negligible. The only way that would change is if someone did something very daft, like exploding a 50mt device down a fault. Even then, the effect could be debatable.
The fact seems to be that nuclear bombs are only as dangerous as the people who control them. As with global warming, the planet will survive. It's inhabitants may not.
Everything's relative. The earth's crust is extremely resilient, and has had to withstand far worse than a batch of nuclear tests over the years.
Our planet has been hit by hundreds of thousands of meteorites, many of which had a far greater yield in terms of energy release than any nuclear test.
The largest in recent history was the meteorite which impacted near the Tunguska river in Russia on 30th June 1908. The meteorite exploded between 5 and 10 kilometres above the ground, and the blast was probably equal to 15 megatons of TNT - that's 1000 times the power of the Hiroshima atomic bomb - with a shock wave equal to 5.0 on the Richter scale.
An explosion like that would easily wipe out a city the size of Manchester and all its suburbs.
There have been many such impacts in the earth's history, and a few a lot bigger - nuclear tests are pinpricks by comparison.
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