Here's how to handle the Seismic Smash tank dispel mechanic on the E.D.N.A fight in The Stonevault dungeon.
Stonevault Overview
Seismic Smash inflicts heavy damage on the Tank and leaves them with a debuff called Seismic Reverberation. Seismic Reverberation leaves the Tank with a DoT effect every 3 seconds for 30 seconds. Once dispelled, it grants the Tank Stone Shield, a 50% Damage Reduction buff that lasts for 6 seconds.
Healers will want to handle this dispel is by holding off on dispelling until the next Seismic Smash is about to cast. The cast time of Seismic Smash is 4 seconds leaving Healers with plenty of time to dispel before it goes off.
The reason for dispelling here is because we want the Tank to have the Stone Shield damage reduction on the heaviest damage intake of the fight.
It is also worth mentioning that Tanks can dodge Seismic Smash, but is not recommended because we want the Stone Shield. Tanks can turn their backs to the boss during the cast time to guarantee they don't dodge.
Here's a general timeline of all the mechanics in motion:
Because the debuff lasts 30 seconds, Tanks will always have the Stone Shield Damage Reduction for Seismic Smash if dispelled at the right time. The first Seismic Smash of the fight is the only time Tanks will not have Stone Shield and so it is recommended to use cooldowns/defensives to live that first cast.