Deformation along an apparent seismic barrier: a palaeoseismological study along the North Anatolian Fault

Abstract

An overstep in the North Anatolian Fault, possibly acting as a seismic barrier, was investigated for its structural and palaeoseismological characteristics. Study interests were: i) to find overstep related spatial changes in deformation which would help assess the structure as a long term singularity in the fault; ii) to identify short term, event-triggered changes in structures where the major fault enters the overstep i.e., in an area where seismogenic slip is impeded or even arrested; iii) to investigate whether or not the surface overstep is related to a seismic barrier, and iv) to discuss structures that might possibly be characteristic of barriers. In order to achieve this: a) largescale faults were mapped in the area, b) fault-slip data were measured in 56 outcrops along and within the overstep, and c) trenches were dug at the eastern rim of the overstep where recent earthquake structures had been reported. Derived long term stretching directions and ratios change significantly over the fault step and structures of recent major earthquakes suggest different deformation mechanisms for different events at the same Location e.g. strike-slip, thrust and normal faulting.