Fully buffed mine is doing 8.9 fire and 8.9 slashing damage per hit, every 3 seconds, for 11.9 seconds. Radius is almost 9m.
Hits, crits, grazes don't seem to make a difference to damage or duration oddly enough.
This means that over 10 seconds it ticks 4 time (0, 3, 6, 9) for a total 71.2 to everything within a huge radius.
At my level that damage is low but if combined with other on hit effects I think it could be more interesting (ie the meteors etc.)