A rigid block rotation model for the GPS derived velocity field along the Ryukyu arc

Using a GPS derived velocity field, we try to estimate the kinematic features of the Ryukyu arc, and discuss its implications to the spreading of the Okinawa trough. The GPS derived strain rate field implies that internal deformation within the Ryukyu arc is not significant, therefore, we adopt a rigid block rotation model for the motion of the Ryukyu arc. The velocity field in the Ryukyu arc is best explained by a model with three blocks rather than one with only one block. The estimated block rotations predict the spreading along the Okinawa trough. The predicted spreading is slow (10 mm per year) in the north and fast (50 mm per year) in the southwest. The direction of the predicted spreading is normal to the Okinawa trough (N170°E–N180°E) in the southwest, while in the north the direction of the spreading is oblique to the Okinawa trough (N150°E–N180°E).