Luk 21:26 people fainting with fear and with foreboding of what is coming on the world. For the powers of the heavens will be shaken.
Why is it that only Luke mentions this marine aspect of the birth pangs?
The answer is sublime. Luke's temple discourse has the gentiles as it's target audience, that is all the peoples around the world.
Matthew and Mark's Olivet discourse accounts, a private one with just the disciples, have those living in Jerusalem at the time of the birth pangs as their target audience. As such, they are protected from the worst of the ravages of the marine disturbance by the Mediterranean sea.
If one is disposed to question this, consider:- The other three evangelists are all Jewish, Matthew, Mark and John. These three were directly appointed by the Lord in His earthly ministry. Only Luke "comes in from the cold" of the gentiles.
Luke is the faithful companion of Paul, the apostle to the gentiles.