Palaeoseismic behaviour of strike-slip faults in slowly deforming regions: palaeoearthquakes and long-term slip history of the Ovacık Fault (eastern Turkey)

The Ovacık Fault (OF) is one of the internal structures of the Anatolian Block, located close to its eastern boundary. Although it shows a very clear surface trace, there are no instrumentally recorded surface rupturing earthquakes on this fault. This study concludes results of the first palaeoseismological trench study on the OF with the evidence for three surface rupturing earthquakes for the last 6 kyr. Structural, stratigraphical and geochronological constraints show that the oldest event happened between 4700 and 3022 BCE, whereas the penultimate event was between 2262 and 1643 BCE. The youngest event happened after 56 BCE, which we could only delimit from below because of the absence of any dateable material from the upper layers of the relevant horizons. The derived mean interevent time of these three palaeoevents is 2400 ± 765 years. We could not correlate any of these palaeoevents with historical earthquakes due to the absence of records in catalogues for the region of interest. Moreover, we used cumulative offsets of the major drainages to calculate the long-term slip rate of 2.7 mm/year since the Pliocene, which exceeds slip rates of other internal faults of Anatolia almost by the factor of two. Our results do not only show significant deformation for the internal parts of Anatolia but also point out a seismic potential of the OF.