Source characteristics of the 6 June 2000 Orta–Çankırı (central Turkey) earthquake: a synthesis of seismological, geological and geodetic (InSAR) observations, and internal deformation of the Anatolian plate

Abstract

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.

Shallow and Deep Structure of a Supradetachment Basin Based on Geological, Conventional Deep Seismic Reflection Sections and Gravity Data in the Buyuk Menderes Graben, Western Anatolia

“…This seismicity is closely associated with major tectonic structures in the area. The focal depths of the earthquakes in Western Anatolia range from very shallow to 50 km (Yılmaztürk et al 1999;Akyol et al 2006;Taymaz and Price 1992;Taymaz 1993Taymaz , 1996Taymaz et al 1990Taymaz et al , 1991Taymaz et al , 2007. Large earthquakes in Western Anatolia usually centre close to the base of the brittle upper crust.…”

The Ilica Branch of the Southeastern Eskişehir Fault Zone: An Active Rightlateral Strike-Slip Structure in Central Anatolia, Turkey

“…The thermochronological data from the Uludağ massif suggest that the initiation age of the EFZ dates back to Oligocene times (Okay et al, 2008). The regional importance of the EFZ as an eastern border of the West Anatolian Extensional Province has also been emphasized by Koçyiğit and Özacar (2003), especially in light of the normal fault-induced Sultandağ and Çay earthquakes (Taymaz and Tan, 2001;Başokur et al, 2002;Emre et al, 2003).…”

Interseismic strain accumulation across the central North Anatolian Fault from iteratively unwrapped InSAR measurements

“…There is a relatively sharp change in fault‐parallel velocity south of the NAF (Figure ) that coincides with the B‐B′ profile line. We believe that this is due to a combination of postseismic deformation from the 2000 Orta earthquake ( M w 6) [ Taymaz et al , ], residual atmosphere introduced mainly from ascending track 71, and postseismic deformation from the 1999 Izmit and Düzce earthquakes.…”