Corrupted Aether and Allagan Technology.

[Sotek]

It's not Allagan technology.

http://eu.finalfantasyxiv.com/lodest...cc8eb228a2eade

So it was that a lighthouse was constructed at the end of the Sixth Astral Era. For a time this structure would serve seafarers well, ensuring safe passage through the Navigator's waters. Fueled by an aether generator designed by Naldiq & Vymelli's, Pharos Sirius was the guiding light of Limsa.

As for why most of the corrupted crystals have Allagan technology nearby; Dalamud was Allagan technology, debris from Dalamud that fell during Brohamuts attack messed with the aether.