Eschatological earthquakes

 2 For I will gather all the nations against Jerusalem to battle, and the city shall be taken and the houses plundered and the women raped. Half of the city shall go out into exile, but the rest of the people shall not be cut off from the city. 3 Then the Lord will go out and fight against those nations as when he fights on a day of battle. 4 On that day his feet shall stand on the Mount of Olives that lies before Jerusalem on the east, and the Mount of Olives shall be split in two from east to west by a very wide valley, so that one half of the Mount shall move northward, and the other half southward. 5 And you shall flee to the valley of my mountains, for the valley of the mountains shall reach to Azal. And you shall flee as you fled from the earthquake in the days of Uzziah king of Judah. Then the Lord my God will come, and all the holy ones with him (Zech 14:2-5).

The gist of this oracle is a supernatural earthquake that provides an escape route for Jerusalemites while walling off their retreat from the invaders. The invading army is on the wrong side of the new hill to pursue them.

The oracle trades on the fact that parts of the Middle East are seismically active. To a modern reader, there's nothing surprising about the imagery. Seismologists and geologists study faults which preserve trace evidence of massive ancient earthquakes that reshaped the landscape. And they make projections about future earthquakes. 

But it's anachronistic to read the text that way, in the sense that while the original audience was acquainted with earthquakes (v5), they had no experience of earthquakes sufficiently cataclysmic to transform the topography in the way this text describes. An earthquake that massive would kill all the inhabitants. There'd be no surviving observers to transmit memories of the disaster. 

So the text reflects a knowledge of tectonic activity that's hard to explain if OT prophets were merely children of their time. They never witnessed an earthquake on the scale necessary to have anything remotely resembling the impact described in the text. So how could they extrapolate from lesser earthquakes? That's an issue whether we construe the oracle literally or figuratively.