Yes, I do believe it will be as you say, a one mile wide impact will most likely occur. The reason the sea turns to blood is because it is God’s judgment falling upon mankind. There are thousand of huge asteroids out there that we can not see. For sure one of them has the name earth written all over it.
But we will not be here, praise God, Jesus will save us from the trial that is coming upon those who live on the earth. I pray that I will be counted worthy to leave this place and be with our Lord Jesus when He comes!