Stress Field Pattern in the Northeastern Part of Azerbaijan

Abstract

Azerbaijan is characterized by a strong level of seismicity with earthquakes concentrated within several active areas. In this study, we calculated the source mechanism of earthquakes occurring in the northeastern part of Azerbaijan, by using the digital waveform data recorded by the Republican Seismic Survey Center (RSSC) at the Azerbaijan National Academy of Sciences (ANAS) during the period from 2003 to 2017. Polarity of the first motion of a P-wave was the main criteria for focal mechanism solutions with high reliability. In investigation of the different tectonic deformations and modern stress field pattern in the tectonic areas of the northeastern part of Azerbaijan, the focal mechanism solutions were applied. The results show mainly a thrust faulting mechanism with few events displaying also normal faulting or strike-slip faulting. The World Stress Map (WSM) Create A Stress Map Online (CASMO) and Cataclastic Analysis Method are used in the current research for defining the regional stress field orientations. Western and central parts of the Greater Caucasus ridge are mainly characterized by northeastern–southwestern (NE–SW) tension. In the eastern part, the tension reverses into intensive compression. Additionally, the transformation of sinistral strike-slip motion into predominant right-lateral strike-slip motion can be obviously traced southward from mountain ridges of the Greater Caucasus. The differences between these characteristics are considered for the large tectonic zones (Balaken–Zagatala, Sheki–Oguz–Gabala, Ismailli–Shamakhi). In the Zagatala region of the studied area, the NW–SE orientation of the compression axes is observed, while in the Sheki region, orientation stretches towards N–S and smoothly extends clockwise towards NE–SW orientation in the Caspian Sea. The tension axis is mostly directed towards NE–SW and N–S which is linked with the heat of the Kur depression under the zone of the Greater Caucasus. Significant spatial variations in orientations of the axes of principal stresses in the shear zone and their local weak gentle variations are evidence of a consistent general stress in the NE–SW direction.