[renormalised (Carl)]

The depression is a lot earlier than they are. It would've had to form, partially infill then several series of graben came along, and then they were filled to partially filled, again. Then you have later extension and then compression. All the while there's been craters forming....some are older than the E/W trending graben, they're cut by the graben. Others are younger, they cut the graben off. If you look in the middle of the plain, you'll see two NW/SE tending gashes, only small. They're graben but they've failed to develop anymore than as a short gash through the plain. I'd say they're formed through a slight adjustment of the basement rocks in the area, nothing more than a jostle...you can see one of the earlier E/W graben (a small one) has part of its valley slightly displaced along the trend of those graben I've just mentioned...it's been faulted in that direction.