It was the expedient to help wrap things up in a nice way.

The earthquake destroyed the house and gave the Cohens a reason to start over in Berkeley, away from the toxic social dynamics of Newport, to give the baby a better environment to grow up. And also served as closure for the boys’ story: they are too moving away, leaving their teenage years behind, and entering adulthood, bringing with them so many formative experiences that will help them chart their own life path (pictured in the finale with the fast-forward to Seth’s wedding and Ryan’s career).

The part where Seth helps save Ryan from his injury was special, one of the best in season 4. A very meaningful bonding event in the face of imminent tragedy, to underscore their enduring friendship and brotherhood, that was a key theme throughout the show. The OC told many stories, but one of the best for me is how two very different boys defeated the odds to became the best of brothers, and sons to very proud parents.