Darkquake

The Darkquake occurred in 1497:Contact towards the end of the Age of Contact, and is the most devastating earthquake Runetalras has experienced in all its known history. It brought an end to the greatest empire of the subterranean world Orzar’Nack.
The Darkquake was a remarkably strange and powerful earthquake for a number of reasons. Firstly, the Darkquake seems to have primarily affected the subterranean world and the Underdark, with most of the surface world unaware that it took place. Secondly, the earthquake seems to have no epicentre, with the earthquake being as devastating in the north of the Atarsid Isles as it was in the south of Talduras and Taunas, which is very much unlike any other earthquake in the known history of Runetalras. Finally, historian have discovered that the Darkquake appears to have occurred at the same time throughout all Runetalras.
It was the Darkquake that brought an end to the Orzar’Nack empire, as it destroyed the vast majority of the Darkroad, the subterranean highways which connected the empire, as well as large numbers of cities and towns. The number killed within the Orzar’Nack during the Darkquake is believed to range from the hundreds of thousands to millions, while the number killed in the Underdark is totally unknown to surface scholars.
During the Darkquake whole subterranean cities were swallowed up and thought destroyed and lost by the rest of the chaotic Orzar’Nack Empire. Not all the dwarves and gnomes in these cities died, although soon the living learnt to envy the dead; these dwarves and gnomes were captured and enslaved by the illithid who performed vile experiments and twisted the dwarves into the Duergar and gnomes in Deep Gnomes.
The Duergar believed that they were the last of the dwarves, and that no others survived the Darkquake, as they knew their kin could not have abandoned them to their horrific fate. After the Illithid Wars when the Duergar broke away from their slavery they descovered that other dwarves survived the Darkquake, and futher descoved that the dwarves knew the fate that befell the Duergar and refused to help for fear of the drawing the ire of the illithid. The Duergar were filled with anger, rage, and disappointment in their kin who had betrayed them and broken countless oaths; this feeling of betrayal is still strong in the Duergar today who have sworn vengeance upon their kin.