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This paper is concerned with the seismotectonics of the North Anatolian Fault in the vicinity of the Orta-Ç ankırı region, and consists of a study of a moderate-sized (Mw ¼ 6. 0) earthquake that occurred on 6 June 2000. The instrumental epicentre of this earthquake is far from the North Anatolian Fault Zone (NAFZ), and rapid focal mechanism solutions of USGS-NEIC and Harvard-CMT also demonstrate that this earthquake is not directly related to the right-lateral movement of the North Anatolian Fault. This earthquake is the only instrumentally recorded event of magnitude (Mw) .5.5 since 1900 between Ankara and Ç ankırı, and therefore provides valuable data to improve our understanding of the neotectonic framework of NW central Anatolia. Field observations carried out in the vicinity of Orta town and neighbouring villages immediately after the earthquake indicated no apparent surface rupture, but the reported damage was most intense in the villages to the SW of Orta. We used teleseismic long-period P-and SH-body waveforms and first-motion polarities of P-waves, broadband P-waves, and InSAR data to determine the source parameters of the 6 June 2000 (Orta-Ç ankırı, t o ¼ 02:41:53.2, Mw ¼ 6. 0) earthquake. We compared the shapes and amplitudes of long-period P-and SH-waveforms recorded by GDSN stations in the distance range 30-908, for which signal amplitudes were large enough, with synthetic waveforms. The best-fitting fault-plane solution of the Orta-Ç ankırı earthquake shows normal faulting with a left-lateral component with no apparent surface rupture in the vicinity of the epicentre. The source parameters and uncertainties of this earthquake were: Nodal Plane 1: strike 28 + 58, dip 468 + 58, rake -298 + 58; Nodal Plane 2: strike 1138, dip 708, rake -1328; principal axes: P ¼ 3388 (488), T ¼ 2328 (148), B ¼ 1318 (398); focal depth 8+2 km (though this does not include uncertainty related to velocity structure), and seismic moment M o ¼ (140-185) Â 10 16 N m. Furthermore, analysis of a coseismic interferogram also allows the source mechanism and location of the earthquake to be determined. The InSAR data suggest that the north-south fault plane (Nodal Plane 1 above) was the one that ruptured during the earthquake. The InSAR mechanism is in good agreement with the minimum misfit solution of P-and SH-waveforms. Although the magnitude of slip was poorly constrained, trade-off with the depth range of faulting accurred such that solutions with a large depth range had small values of slip and vice versa. The misfit was small and the geodetic moment constant for fault slips greater than c.

A catalog for earthquakes that occurred in western Turkey during the period 1964-2010 is compiled for achieving homogeneity for magnitudes. Data are obtained from the International Seismological Center (ISC), where earthquake magnitudes are reported in different scales and come from a variety of sources. For establishing a common magnitude expression, namely an equivalent moment magnitude M w , new relations correlating the different magnitude scales with each other are derived from converting as many as possible of the magnitudes reported in the ISC bulletins. After magnitude conversions, the completeness magnitude M c is sought by modifying the goodness-of-fit method of Wiemer and Wyss (2000) to become more appropriate for datasets with smaller sample size and higher M c thresholds. The study region is divided into four smaller regions on the basis of spatial data homogeneity, while different periods of similar seismic network performance are recognized and tested to seek spatiotemporal variation of M c . The results derived in each case are compared with those yielded by the application of both the original goodness-offit and maximum curvature methods and are found to be quite similar, although there are still cases with a difference exceeding 0.3 magnitude units. The goodness-of-fit method is very sensitive in the selection of the desirable percentage of fitting a power law (90% or 95%), whereas the proposed modification makes it independent of this level selection, and performing better especially for datasets that include events before 1990, when higher completeness magnitudes are evident.Online Material: Earthquake catalog with equivalent moment magnitude for western Turkey.