Hello Cathryn,
OK....GPS stations were a little sparse before 1999 quakes...and the motions afterwards are swamped by post quake effects...they have some of the same problems in California. Also...with sea of Marmara sitting over large area, there are no GPS data there....so where the south branch runs along the south coast, and the north branch is well offshore of the north coast, you can tell what the motion of the blocks is but it is hard to tell how much is on which fault. They have a similar problem with the San Andreas fault and San Jacinto fault...both are locked so displacement is seen over large width...and because the 2 faults are not all that far apart, especially in the north, it is hard to tell from GPS how much slip is on which...
Chris