“So they called out to the LORD: “Please, LORD, don’t let us perish because of this man’s life, and don’t charge us with innocent blood! For you, LORD, have done just as you pleased.” 15 Then they picked up Jonah and threw him into the sea, and the sea stopped its raging. 16 The men were seized by great fear of the LORD, and they offered a sacrifice to the LORD and made vows.” Jonah 1:14-16
Note the reaction of the sailors to the great calm after throwing Jonah overboard to a certain death. They were used to experiencing storms at sea, admittedly perhaps not one this bad; but storms at sea were part of the natural world they lived in. However, never was there a sudden calm following one. They received relief more than they could have ever dreamed of, but it produced more fear in them than the violent storm had.
The miracle of a peaceful sea on which to set sail again led them to worship Yahweh alone. Never again would they look to the ineffectual gods they had called upon during the storm. The Lord had proved to them which deity was the true God.
Their fear was the proper response to the Lord’s supernatural intervention.