Interseismic GPS velocities in Sakhalin indicate that the island moves to the west at 3--4 mm/yr with respect to the Eurasian plate, which is about half of the relative Eurasia - North America plate convergence rate. GPS measurements across the central Sakhalin fault system provide evidence of compressive and strike-slip strain accumulation at a rate ≤3 mm/yr. Coseismic vertical displacements produced by the August 4, 2000 Mw 6.8 Uglegorsk earthquake in Sakhalin were analyzed by constrained nonlinear inversion which provided evidence for a reverse faulting mechanism on an east-dipping fault plane.