Postseismic Deformation near the Izmit Earthquake (17 August 1999, M 7.5) Rupture Zone

We present and interpret the results of postseismic, Global Positioning System monitoring of the first 298 days following the 17 August 1999 Izmit earth- quake. Whereas the data suggest some spatial and temporal complexity in the post- seismic motions, the overall pattern can be characterized by time-dependent relaxa- tion functions and suggests exponential decay with an estimated 57-day relaxation time. The very rapid deformation during the first few weeks following the mainshock suggests rapid afterslip on and below the coseismic rupture segments. The exponen- tial decay of the postseismic deformations through the end of the observation period suggests contributions from the lower crustal viscoelastic relaxation.