It was the embodiment of what the human body can reach—the strength to split the world in two and cause earthquakes with a single strike. Kera was divided in half after the unsealed Amelio struck the ground, and not even Arthur expected such strength.
After seeing the stats of Amelio, Arthur assumed the seal took away half of his strength. However, after seeing it for real, Arthur realized it was much more. He always knew that stats did not equate to power, but he never understood how exponential the relationship was.
A mere shockwave made the soldiers and gobkins get thrown away, along with Arthur and the guild masters. Then, as the crack extended to cover the entirety of the city, it broke the pillars. The two sides of the gap, which span tens of meters, became two separate worlds, one rising and the other sinking.