A B737-700 crew encounter wake turbulence on the LAX SEAVU TWO ARRIVAL and because the upset distraction and fatigue failed to transition to Runway 24R from the preplanned Runway 25L arrival.

Narrative

While on the SEAVU TWO into LAX we encounter wake turbulence from an aircraft that was ahead of us. The autopilot was disengaged to right the aircraft. At this time ATC gave us our approach clearance. We heard that we had been cleared for the SEAVU TWO ARRIVAL to intercept the 25L localizer and cleared for the approach. We were then told to change frequencies. The next controller asked which localizer we were tracking. We told him 25L. He told us we were supposed to be on 24R. He then told us to turn right 10 degrees and intercept the 24R localizer and cleared for the approach. There were no other problems with the approach. We preplanned to fly the arrival to 25L off of the SEAVU ARRIVAL. We encountered the wake turbulence just as we received our approach clearance. We were also fatigued from flying the flight to LAX. We were also delayed due to last minute maintenance item that had come up just before our push off the gate. This combined with the wake turbulence acting as a distraction at the time the clearance for the approach was given lead to the incorrect approach being flown. Two things can be done to prevent this from occurring in the future. 1. If wake turbulence or any other type of distraction happens when a critical clearance is give the distraction should be stated to the controller and a request for clarification of the clearance should be obtained. 2. SOCAL approach can be asked to give the arrivals a heads up on which runway they can expect to be give before clearing the aircraft for its approach. We have already been given the STAR into the airport but not the runway. If they could give us the runway to expect earlier it would reduce the chances of error during the high workload phase of flight