I've argued before in this forum that Mark wanted to have Jesus seem to be the messiah whose existence he believed--or pretended to believe--was prophesied, foreshadowed, or prefigured, by persons and events found in Scripture, so he scoured the writings of the prophets for these stories, and adapted them to fit Jesus. I believe the striking parallels below show almost conclusively that Mark's story about Jesus stilling the storm was adapted from Jonah, and is fictional.
In Jonah, a violent storm threatens a ship on which Jonah sleeps, so Mark made a violent storm threaten a ship on which Jesus sleeps. In Jonah, the apprehensive sailors waken Jonah and question his cavalier attitude toward the danger, so Mark made his boat's captain apprehensive also, and had him, too, waken Jesus and question him about his seeming lack of concern. The miraculous calming of the sea in Jonah causes the men to fear the Lord, so Mark has the miraculous calming of his sea make the disciples fear Jesus, too. (Jonah 1:4-16, Mark 4:37-41)
Here are the relevant verses:
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[S]uch a violent storm arose that the ship threatened to break up. (Jonah 1:4)
A furious squall came up, and the waves broke over the boat, so that it was nearly swamped. (Mark 4:37)
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Jonah...fell into a deep sleep. The captain went to him and said, "How can you sleep? (Jonah 1:5-6)
Jesus was…sleeping... The disciples woke him and said to him, "Teacher, don't you care if we drown?" (Mark 4:38)
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[T]he raging sea grew calm. At this the men greatly feared the LORD (Jonah 1:15-16)
Then the wind died down and it was completely calm.They were terrified and asked each other, "Who is this?” (Mark 4:39-41)
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Joseph F. Alward
"Skeptical Views of Christianity and the Bible"