The writer speaks of the deepest part of the sea as if it were the sea's heart. Here he describes an earthquake that causes the mountains to crumble and fall into the sea. This can be stated in active form. Alternate translation: "the mountains should shake so violently that they fall into the depths of the sea" (See: [[rc://en/ta/man/translate/figs-metaphor]] and [[rc://en/ta/man/translate/figs-activepassive]])