Displacements and Kinematics of the February 1, 1944 Gerede Earthquake (North Anatolian Fault System, Turkey): Geodetic and Geological Constraints

Authors: MEHMET EMİN AYHAN, ALİ KOÇYİĞİT

Abstract: The North Anatolian Fault System (NAFS) is an approximately 2-110-km-wide, 1600-km-long right-lateral intra-continental transform fault boundary between the Anatolian platelet and the Eurasian plate. The Gerede fault zone is one of the major active structures in the western section of the NAFS. It is a 1-9-km-wide, 325-km-long and ENE-trending dextral strike-slip fault zone, with a total accumulated offset since its initiation (Late Pliocene) of about 43 km. This offset indicates an average geological slip rate of 16.5 mm/yr. The 1 February 1944 Gerede earthquake occurred within the Gerede fault zone. Based on recent field geological mapping of the rupture traces and offsets on it, the average and peak lateral offsets were measured to be 4.37 m and 7.16 m, respectively. A triangulation network covering the region was first set up between 1936 and 1943. Twentyeigth existing points of the network were reoccupied by GPS receivers between 1995 and 2004. Coseismic displacements for the February 1, 1944 Gerede earthquake were obtained at the reoccupation points by removing interseismic deformation and coseismic displacements of recent earthquakes. Modelling the coseismic displacements in elastic half space resulted in a rupture surface slippage of 4.40 ± 0.11 m and 1.02 ± 0.17 m in dextral and normal dip-slip directions, respectively. The 191-km-long and 16-km-deep rupture surface strikes N76°E and dips at 85° ± 5° both to north and south. In the present study the estimated geodetic scalar moment and moment magnitudes are M_o= 4.02 x 10^{20} Nm and M_w= 7.74, respectively. The rupture surface was extended down dip to a depth of about 28 km, and a significant slip distribution was recovered. Based on both the geodetic and geological data, the recurrence intervals for great seismic events to be sourced from the Gerede fault zone were calculated as 232 ± 25 years and 266 ± 35 years, respectively.

Keywords: North Anatolian Fault System, Gerede fault zone, Gerede earthquake, coseismic deformation, GPS, triangulation

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