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The arc-shaped Bozgush Mountains is a remarkable morphological feature bounded by active faults in northwest Iran. The southern and northern parts of the mountain belt are limited by the South and North Bozgush Fault Zones, which produced numerous destructive earthquakes in historical and instrumental periods. We employed the Sentinel-1A Differential Interferometric Synthetic Aperture Radar (DInSAR) method to map the deformation details of the November 08, 2019, Turkmanchay earthquake (Mw: 5.9) along the South Bozgush Fault Zone to understand the earthquake-triggered surface deformations and seismogenic faulting characteristics. The results of the DInSAR time-series analysis show that subsidence and uplift range from − 5 cm to + 6 cm, respectively. The total line of sight (LOS) displacement was approximately 11 cm. Interferogram fringes and deformation patterns indicate that the direction of the potential seismogenic fault is WNW-ESE. These patterns are consistent with the orientation of the South Bozgush Fault Zone, including primarily right-lateral strike-slip characteristics with reverse components. Continuous patterns of the obtained interferogram fringes indicate that surface rupture did not occur during the earthquake. Our Coulomb failure function results in preferred faults derived from geological structures, indicating that the stress rate was positive and high in several segments of the South and North Bozgush Faults, revealing that the main earthquake event might trigger those faults. The large aftershocks that occurred on the same faults supported our results, and the distribution of aftershocks in the Bozgush Mountains suggests that the WNW-ESE orientation is consistent with the orientation of segments constituting the South Bozgush Fault Zone. [ABSTRACT FROM AUTHOR]

We investigate correlation between the Coulomb stress changes and the spatial distribution of the aftershocks of the 1990 Mw 7.3 Rudbar earthquake that occurred on and off the Rudbar fault. The Coulomb stress changes indicate that the Rudbar mainshock encouraged parts of the Kelishom and Kashachal strike-slip faults (located east of the main rupture), as well as parts of the Manjil Thaist fault (located south of the main rupture). The central part of the Manjil Thrust, which is sandwiched between two stress shadow zones, experienced an increase in Coulomb stress. We observe that the events before and after the Rudbar mainshock have different spatial distribution patterns. We find that most of the aftershocks occurred in an area between the Kabateh and Zardgeli segments where the static Coulomb stress is high, while few aftershocks occurred in the stress shadow zone that extends to the northwest and southeast of the Rudbar rupture. The aftershocks that occurred in the stress shadow zones northwest of the Baklor segment were related to the continuation of the background seismicity after the mainshock. A burst of seismicity following the Rudbar earthquake south of the Zardgeli segment provides evidence for dynamic stress triggering for the aftershocks that affected these regions for the first 1-3 months after the mainshock. We also compare the Coulomb stress changes with the seismicity rate and find that the regions with high seismicity rate are in good agreement with the high stress such as the western end of the Baklor and an area between the Kabateh and Zardgeli segments. To validate the effects of the Coulomb stress on the seismicity rate, we resolved stress changes on the aftershock nodal planes and recognize that the aftershocks located between the Kabateh and Zardgeli segments and the surrounding areas were brought closer to failure. [ABSTRACT FROM AUTHOR]

In this work, we investigate the Mw 5.9 earthquake occurred on 7 November 2019 in the East-Azerbaijan region, in northwestern Iran, which is inserted in the tectonic framework of the East-Azerbaijan Plateau, a complex mountain belt that contains internal major fold-and-thrust belts. We first analyze the Differential Synthetic Aperture Radar Interferometry (DInSAR) measurements obtained by processing the data collected by the Sentinel-1 constellation along ascending and descending orbits; then, we invert the achieved results through analytical modelling, in order to better constrain the geometry and characteristics of the seismogenic source. The retrieved fault model shows a rather shallow seismic structure, with a center depth at about 3 km, approximately NE–SW-striking and southeast-dipping, characterized by a left-lateral strike-slip fault mechanism (strike = 29.17°, dip = 79.29°, rake = −4.94°) and by a maximum slip of 0.80 m. By comparing the inferred fault with the already published geological structures, the retrieved solution reveals a minor fault not reported in the geological maps available in the open literature, whose kinematics is compatible with that of the surrounding structures, with the local and regional stress states and with the performed field observations. Moreover, by taking into account the surrounding geological structures reported in literature, we also use the retrieved fault model to calculate the Coulomb Failure Function at the nearby receiver faults. We show that this event may have encouraged, with a positive loading, the activation of the considered receiver faults. This is also confirmed by the distribution of the aftershocks that occurred near the considered surrounding structures. The analysis of the seismic events nucleated along the left-lateral strike-slip minor faults of the East-Azerbaijan Plateau, such as the one analyzed in this work, is essential to improve our knowledge on the seismic hazard estimation in northwestern Iran. [ABSTRACT FROM AUTHOR]