A RECENT EXAMPLE OF ACTIVE INTRAPLATE DEFORMATION IN THE CENTRAL ANATOLIA, TURKEY: OBRUK-BOR (NIGDE) EARTHQUAKES

Salt Lake (Tuz GoIti) basin is evident morphological trace in the Central Anatolia which is one of the biggest tectonic lakes in Turkey. Salt Lake basin is NW-SE trending sediment basin and generally restricted by NW-SE trending strike-slip faults which is called the Salt Lake Fault Zone (SLFZ), SLFZ is the biggest faulting zone with 200 km length in the Central Anatolia, Also, SLFZ is a kind of intraplate zone of active deformation characterized by oblique right lateral strike-slip faulting. SLFZ did not produce strong earthquakes last a couple of hundred years which is surrounded by Aksaray Fault and Hasandagi volcanic rise, Seismicity in Salt Lake and surrounding region is quite low, because of inland deformation of Anatolian plate. However recent years several moderate earthquakes (M>5) and aftershocks in the region showed that the rim of the northwest of the SLFZ and especially secondary faults in Bala-Kulu were active parts of the SLFZ. Due to these activities along the SLFZ it is decided to monitor micro seismic activity (M<2.5) by establishing low magnitude threshold seismic network. For this purpose. six broadband seismic stations have been established since 2010 to control the entire region. Obruk-Nigde is located at the southern end of the SLFZ, whose dominant direction is NW-SE. On Sunday 20 September 2020 moderate sized (Mw.5.1) earthquake occurred at the locality approximately 4 km NE of Obruk Village (BorNigde) Central Turkey. The earthquake has been one of the rare earthquakes in the region in the last century. 143 masonry-adobe houses were damaged in village of Obruk of Bor district. The earthquake activity that occurred has activated the secondary NW-SE trending active fault segments parallel to the main fault zone in the region. In this context, the broken fault was in NW-SE direction. The depths of the earthquakes were located in the range of 8-10 km and shallow crustal earthquakes. In this study, focal mechanisms of 8 earthquakes (M>4) are calculated using moment tensor inversion from broadband stations. Fault plane solutions made within the scope of the study reveals that the region continues its tectonic evolution under the influence of the strike-slip regime. Moment Tensor solutions show that mainshock and important aftershocks obviously revealed that the SLFZ is being dominated by NW-SE trending dextral strike-slip faulting. Aftershock locations are correlated with fault plane orientations, Recent earthquakes have revealed the presence and activity of small fault segments parallel to the main fault segments in the SLFZ in the region. The results of the stress tensor analysis conducted within the scope of the study show that the main stress T axis is in the NW-SE direction and the maximum stress P axes are in the NE-SW direction.