I have to be careful not to project too much of my own sense of the real world situation into things (as opposed to what's in the text), so feel free to call me on that.
The Concern of the Past as I see it comes from the fact that this single moment (well, a series of events from July to August of 1974) is completely defining the lives of everyone on the island. Something broke, and there's literally no way to get past it. Joanna can't get over the death of her father. The secret society is drawing its inspiration from the Past. And the Turks have their own conception of the Past that is entirely at odds with the narrative the Greeks are telling themselves. There's simply no way they could ever learn to get along without either a) coming to some kind of agreement about what really happened and what it means or b) agreeing to let go of the past. But until then, the island is frozen in a single moment in time (symbolized by abandoned Varosha-- where there are still clothes hanging on lines).
Initially I had jumped to the Element quad, and then Mike pointed out "Interdiction" as the OS Issue was kind of amazing -- everyone is prevented from crossing the Green Line. (EDIT: I almost forgot -- the Turkish invasion itself was an "intervention" -- especially from their point of view.)
Elias is constantly Conceptualizing schemes that cause problems. Some of this could be tied in with broader Manipulations -- or could be a signpost, I guess.
Mike also pointed out that Conceptualizing is also "visualizing". So being forced to Conceptualize the idea of Elias and Joanna together drives Petros crazy. (Okay, I see how this could also sound like Conceiving).
Memories: the romantic relationship between Petros and Joanna is deeply rooted in memory (though this is shown primarily through Petros' POV). The memories of Joanna's father and Petros' attempt to recapture them (by recovering the photograph) is central to the growth of their relationship. But also when Petros learns that the those memories are not all they might seem, there is an implicit threat to the relationship -- what will it do to them if he brings back things that should have been left undiscovered?