To unlock the "SCORCHED EARTH" trophy in Detroit: Become Human, you must allow Connor or Markus to blow up Jericho during the chapter "CROSSROADS".
I am not sure at this point what triggers the option for Connor to detonate the freighter in Markus' place, but I suspect it may simply be whether or not Markus dies before this chapter begins. This guide will be updated when that has been worked out.
So assuming Markus and Connor have both made it to "CROSSROADS", you simply need to let everything play out until Connor confronts Markus. In my playthrough I allowed Connor to become deviant and spare Markus, thereby also earning this trophy:
Eventually when the FBI enter the freighter you will have to make a decision about how to escape. Make sure Markus chooses to detonate Jericho. Make sure to keep Markus alive through several QTEs and decision points until he gets to the bombs. I was able to intervene in each incident along the way and survive just by passing the QTEs. I also chose the left-hand path when you are presented with two escape routes during discovery by the police. Markus will get attacked one last time while trying to arm the bombs. Once he is done, let the rest of the chapter play out as you see fit. As long as the ship explodes at the end you should unlock this trophy when you reach the flowcharts.