A Surface-Breaking Capable Fault in the Greater Caucasus: New Evidence from the 123-km-Long Kur Fault, Azerbaijan

In this work, we present the results of a structural and geological investigation carried out along the 123-km-long Kur Fault, the frontal structure of the Kura Fold-and-Thrust Belt (Greater Caucasus, Azerbaijan). For the first time, field surveys and paleoseismological trenching revealed a fault plane that reaches the surface along this regional structure, exposing a clear tectonic contact where Lower Pleistocene deposits overthrust Holocene sediments. This observation is crucial, as it demonstrates that the frontal fault of the Greater Caucasus is a capable fault, despite the lack of strong historical earthquakes reported in the area.

In addition to the tectonic contact described above, the Lower Pleistocene deposits exposed in the trench are cut by numerous fault planes, allowing us to reconstruct a stress tensor indicating a purely compressive regime, characterised by reverse dip-slip motion and a horizontal σ₁ oriented NNE–SSW. The orientation of this σ₁ is parallel to both the GPS velocity vectors and the P-axes of available focal mechanisms, suggesting that a NNE–SSW compressional stress field has remained stable from the Pleistocene to the present day. This σ₁ direction is also orthogonal to the regional strike of the Kur Fault (WNW–ESE) and matches the orientation observed at the trench site.

In the same area of the trench site, we identified three distinct river terraces associated with the Kura River. The uppermost and oldest terrace is currently uplifted to 37 m above the modern river level and has been dated to 10 kyr using the OSL method; it displays a tilting of about 5°, consistent with the kinematics of the Kur Fault. The most recent and lowest terrace lies 4–6 m above the present river level, also indicating recent uplift and tilting of the palaeoterraces as a result of active tectonics along the Kur Fault.

Geological evidence from the trench site, combined with uplift data from the river terraces, indicate an average Holocene shortening rate that is greater than the value inferred from GPS measurements. Additionally, the exposed fault plane corresponds to a ~31-km-long segment of the Kur Fault which, based on empirical scaling relationships, is capable of generating an earthquake of approximately M 6.8.

The work was carried out entirely through field data collected during two dedicated campaigns within the framework of the NATO Project G5907 – Science for Peace and Security Programme, which focuses on geohazard assessment around the Shamkir Hydroelectric Power Station (https://shamkirproject.unimib.it/).