If someone says that a place is calm, they mean that it is free from fighting or public disorder, when trouble has recently occurred there or had been expected.
平静的
Calm is used to refer to a quiet, still, or peaceful atmosphere in a place.
安宁
When the sea calms, it becomes still because the wind stops blowing strongly. When the wind calms, it stops blowing strongly.
(海或风) 平静下来
The calm before the storm 暴风雨前的宁静
calm down 镇定下来