You said that the bay was formed by an earthquake that forced up the crescent shaped mountains in the middle there. This would imply that the bay was not there before the earthquake, right? As such the rivers would have been flowing south (probably southwest IMO) before said quake. In order to get the rivers to flow into the newly created bay and still be plausible, the whole middle section of the continent would have to have been raised in order to force them there OR they'd have to be flowing into the fault zone cracks OR said area would have to have been lowered while leaving the mountains in place. I'm just a river deputy so my 2 cents would be to either flatten that crescent mountain shape into hills, cut back some of the crescent mountains to form some drainage lanes, or move that section further south with some lowlands emptying into the bay. This is more of a question for the geologists, though, so I could be way off.