When a character is forced to make a saving throw, take Xd12 damage. The Tremor-count is removed on your next turn, after it has “bursted” or if intiative ends. Tremor-stacks will accumulate until a save is being made.
e.g: you can go 4 turns, and take 2 Tremors per turn to suffer 8d12 damage when being made to take a turn.