When reading any of the three Synoptic versions we notice chunks of stock OT theophanic language salted amidst very specific details.
Some scholars have suggested that these chunks represent how the earliest Markan form actually read. That is, the response to the question posed to Jesus consisted largely of boilerplate OT theophanic (manifestations of divinity and judgement) language accompanying the appearance of the Son of Man:
There will be earthquakes ...famines...roaring and tossing of the sea...trumpet, darkness, failing sun and stars etc. Then the appearance of the Son of Man, which is itself a block of text from Daniel.
Exod. 19:16-18...thunder and lightning, with a thick cloud over the mountain, very loud trumpet blast ...mountain[b] trembled violently
Judg 5:4-5..the earth shook, the heavens poured, the clouds, the mountains quaked before the Lord
Is. 29:6..... the Lord Almighty will come with thunder and earthquake and great noise, with windstorm and tempest...
Ps.77:16-18 The waters saw you, God, and writhed; the very depths were convulsed. The clouds', thunder...the earth trembled and quaked.
Ps 18:7-18....the earth shook and trembled;..darkness, lightning. clouds.
Esther 1:1 (LXX)..voices and a noise, thunders and earthquake, tumult upon the earth.
Is 13:10..The stars of heaven and their constellations will not show their light. The rising sun will be darkened and the moon will not give its light.
Ez 32:7,8...When I snuff you out, I will cover the heavens and darken their stars: I will cover the sun with a cloud,and the moon will not give its light. All the shining lights in the heavens I will darken over you;
Is 5:30...In that day they will roar over it like the roaring of the sea. And if one looks at the land, there is only darkness and distress; even the sun will be darkened by clouds.
Joel 2:10,3: 15,16...the earth shakes, the heavens tremble, the sun and moon are darkened. and the stars no longer shine. ...roar, thunder ...army of locusts
Amos 5:18-20,8:9-11...day of the Lord, darkness not light. I make the sun go down at noon and darken the earth in broad daylight....famine
And of course, Rev. draws heavily on passages like these and repeats the imagery to accompany divine judgement/appearances.
Back to Mark 13. Again, a reader can't help but notice a contrast between these chunks of OT theophanic language and very specific and far less colorful descriptions of being flogged, being in courts, betrayal by family, Jerusalem being surrounded by Romans etc.
It would make a great deal of sense to conclude the original form of Mark included only the boilerplate theophanic language, (earthquakes, lightning, famine, cosmic darkness etc.) culminating in the appearance of the Son of man from Daniel.
This has been discussed before, but as time went on and the events of 70CE and 135CE came and went, it would be only natural to literalize some of that language and add to it with details about the Jewish wars throughout the Roaman world, the devastating earthquakes and how Christians were suffering. The theophanic language of God's appearance being accompanied with earthquakes, turned into a prophecy of earthquakes.
It seems more likely Mark 13 was harmonized with the later recensions, Matt and Luke than Mark having been expanded prior to their use of it. It just pushes out the dating too far.
Microsoft Word - Detering Mk 13 JHC 50.DOC (radikalkritik.de)