There's ways to mitigate the damage. It's rocks falling, typically non-magical bludgeoning damage.
The timers can be pretty sporadic. Sometimes you do have large gaps of time, others, the tremors happen quickly. The randomness is one of the qualities of managing ones resources.
If you don't have bludgeoning resistance, or damage reduction from spells or items, or any of the skills that can avoid the damage to offset those (discipline, parry, tumble being essential skills even a caster considers cross-skilling), then, you are someone who has not prepared for the travel ahead and more preparations are needed. Ghostly Visage is a basic level 2 spell that can be extended into the level 3 slots, any lvl 5/6 arcanist can tolerate the harm to an extent even without needing to make those skill checks.
As for a suggestion to the problem, there is a story as to why the tremors happen, and I would not mind some small quest around the lore that could temporarily add duration between the tremors, even if it would never be a permanent fix, to make travelling in the more combat heavy aspects of below Dvergeheim more manageable.
I think falling rocks used to hit bleeding out folk last I was there, now that was interesting.