Extent and distribution of aseismic slip on the Ismetpasa segment of the North Anatolian Fault (Turkey) from Persistent Scatterer InSAR

We use the Persistent Scatterer InSAR (PSI) technique with elastic dislocation models and geology along the creeping section of the North Anatolian Fault (NAF) at Ismetpasa, to map and deduce the velocity field and the aseismic slip distribution. Revealing the spatiotemporal nature of the creep helped us associate the creep with potential lithological controls, hence providing a new perspective to better understand the underlying causes and mechanisms. The PSI analysis of Envisat ASAR images between 2003 and 2010 reveals a clear picture of surface creep along the fault and a new interseismic velocity field transitioning gradually between the creeping and the locked fault sections. The creep rate is found to fluctuate along a 100 km long section of the fault in a manner similar to that along the Hayward fault, reaching a maximum of similar to 20 +/- 2 mm/yr, close to the far field plate velocity (similar to 25 +/- 1.5 mm/yr). At Ismetpas, a, it is in the range of 8 +/- 2 mm/yr, consistent with the previous geodetic observations. The creeping section appears to extend 30 km further east than those previously reported. Modeling of the PSI data reveals a heterogeneous creep distribution at depth with two main patches confined mostly to the uppermost 5 km portion of the seismogenic crust, releasing annually 6.2 X 10(16) Nm (Mw=5.1) geodetic moment. Our analysis combined with previous studies suggests that creep might have commenced as postseismic deformation following the 1944 earthquake and has evolved to stable fault creep with time. There is a correlation between aseismic surface creep and the geology along the fault as it is in major part associated to rocks with low frictional strength such as the andesitic-basaltic, limestone, and serpentine bodies within the fault zone.