For tactics, notes and more information on this class of spells, see High Seism.
Grand Seism one-shots an Archhydra, Arisen undamaged
First, High Maelstrom is used to eliminate the 5 Sirens. The first Grand Seism is completely ineffective, demonstrating that the spell cannot penetrate through walls. The second Grand Seism is correctly placed and removes 8 out of 10 health bars, effectively killing the Archhydra in one shot.
Grand Seism vs Griffin (demonstration)
A well timed Grand Seism can slay a Griffin in one shot.