A Lunacon panel I didn't get to because of timing issues. Nevertheless, I shall ponder the topic, "Exploring how any civilization survives when trolls and sorcerers are all over the place."
Answer: it doesn't, unless the trolls and sorcerers are law-abiding citizens. Even sufficient of the unlawful type would mean civilization in a hole-in-wall sort of thing, where the people try to live in odd corners.
If they were rare enough, if civilization was organized enough, you would see a lot of defensive building to withstand onslaughts, and highly trained people to deal with it. Assuming, of course, that they are not rare enough to be flukes, in which case they would be brief and impressive disasters with a lot of talk about being ready for the next one. Of course, they would grow more and more rare exactly because it would be hard to have civilization around them, and so civilization would industriously work at eliminating them.
I notice that in Magitek works, like Operation Chaos or "Magic, Inc." you often get an eruption from another world entirely, exactly because a modern-day-equivalent magic world doesn't contain as many possibilities. Even Robin McKinley's Shadows where the eruptions are frequently enough to instruct children in school about them, they are still eruptions.
and then you get the urban fantasy parallel world inside ours, but that one, of course, has many issues with justifying why it's secret, as I have complained so often before.