Evidence for Long-term Quaternary Tectonic Activity of the Pütürge Segment in the East Anatolian Fault System (EAFS) by Using Luminescence and Radiocarbon Dating Methods

Neotectonics of Eastern Türkiye is mainly characterized by immensely complex deformation patterns driven by the convergence between the Arabian Plate and the Eastern Anatolian Plateau. This apparent convergence accommodates a primary intraplate strike-slip fault system, encompassing the North Anatolian Fault Zone (NAFZ) and the East Anatolian Fault System (EAFS). Recent seismic events, such as the 24 January 2020 (Mw6.8) earthquake and the 6 February 2023 doublet earthquake (Mw7.7 and Mw7.6), dramatically highlight the structural intricacy of the region and signify that the conundrum is much broader than initially thought. The ruptures occurred after the two earthquake sets abruptly terminated the onset of the Pütürge segment residing in the EAFS. The segment splits the Şiro Valley in two and is hypothesized to accumulate strain, potentially driven by aseismic creep.

Our multidisciplinary investigations focus on the deformation and seismic potential of the Pütürge segment, emphasizing critical questions regarding its long-term slip rate, uplift rate, and past earthquake cycle. Geochronological methods, including Optically Stimulated Luminescence (OSL) and Radiocarbon (¹⁴C) dating methods, have been applied to Quaternary River terrace deposits along the Şiro Valley. Three distinct terrace levels (T0, T1, and T2) were identified by measuring stratigraphic sections, with thickness of approximately ~1 m, ~11 m, and ~12 m, respectively. These terraces, shaped by predominantly sinistral strike-slip movement with somewhat oblique components, stand out as geologic archives of tectonic and fluvial activity.  The terrace deposits primarily consist of clays, silts, sands with organic material, gravels, and boulder stemming from the Maden Complex and Pütürge Metamorphics, rich in quartz and feldspar. Preliminary OSL dating employing the single-aliquot regenerative dose (SAR) technique on quartz grains from the T1 terrace yielded ages ranging from 11.42 ± 1.97 ka to 28.18 ± 3.00 ka at the Gölkan site and 12.82 ± 0.95 ka to 30.92 ± 4.85 ka at the Yazıca site, located on the northern and southern margins of the Şiro Valley, respectively. Further analyses of samples from additional terrace levels are still ongoing.

These preliminary yet clear findings suggest that the Pütürge segment has experienced significant post-Quaternary tectonic activity. Furthermore, the seismogenesis of the Pütürge segment, in conjunction with known geological information, raises another issue to consider. The fault's seismicity patterns and parameters will be examined in that sense. Spatial and temporal Gutenberg-Richter recurrence parameters are valuable knowledge that helps us to calculate the return periods of apparent and possible scenario earthquakes. The deformation pattern will be tested to see if it is used as a key indicator of how the Valley is heading through and evolving. As the fieldwork, lab tests, and computational modeling have been underway and are close to finalization, this study aims to present preliminary geochronological dating results inferred from Quaternary fluvial terrace formations. Also, it explores their implications for the seismic hazard and tectonic evolution of the East Anatolian Fault System. This study is fully supported by the Scientific and Technological Research Council of Turkey (TÜBİTAK; Project No:122Y266).