Whisk together the water, orange juice, 1/2 cup salt, light brown sugar, garlic powder, oregano, and thyme in a large glass or ceramic bowl. Submerge the pork chops in the brine. Cover the bowl with plastic wrap, and brine in the refrigerator for 1 hour.
Heat grapefruit juice, 1/4 cup brown sugar, and red pepper flakes in a saucepan. Cook and stir until sugar is dissolved and mixture comes to a boil; reduce heat and cook until syrupy, about 15 minutes. Remove 3 tablespoons of the mixture and set aside. Add half of the grapefruit sections to the syrup mixture and cook for 5 to 10 minutes.
Preheat the oven's broiler and set the oven rack about 6 inches from the heat source.
Remove the pork chops from the brine and pat dry. Place the pork chops on a baking sheet lined with tin foil. Brush each side of the chops with the reserved grapefruit juice syrup. Season with salt and pepper. Broil for 7 to 10 minutes on each side and the pork is no longer pink in the center. An instant-read thermometer inserted into the center should read 145 degrees F (63 degrees C).
Place the remaining fresh grapefruit sections on the pork and drizzle relish over the top.