Light blue on that are shallower water.The Borderland is the area where the shallower water is much wider than elsewhere on the west coast. It also shows deep basins (to 2 km water depth), ridges (to sealevel) and islands (parts of ridges.
I already answered whether quakes are at the edges...but I'll add 2 things: there are very large active strike-slip faults all over the Borderland, and some of these can likely have a M7 or 7.5. And, the outer (western) Borderland, even though it has large faults that are likely active, has not had hardly any measured seismicity...the ones the other day were unusual.....
Chris