Abstract
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.
Highlights
On 7 November 2019 (22:47 UTC), a Mw 5.9 earthquake took place in the East-Azerbaijan, in northwestern Iran, about 100 km east of Tabriz, the fourth largest city of Iran, with over two million citizens (Figure 1a)
By comparing our solution with the different focal mechanisms and hypocentral locations provided by the Iranian Seismological Center (IRSC), the United States Geological Survey (USGS), the GEOFON and the CMT, we remark that the geometric parameters of the seismogenic source presented in this study mostly agree with the fault plane solutions proposed by the IRSC
Our model indicates a slip distribution, mainly located near the ground surface, which can explain the displacement field retrieved by the S1 Differential Synthetic Aperture Radar Interferometry (DInSAR) measurements; we can suggest that our solution can be considered compatible with a shallow source of the earthquake occurring in the complex tectonic setting of the Bozgush Range [7,8]
Summary
On 7 November 2019 (22:47 UTC), a Mw 5.9 earthquake took place in the East-Azerbaijan (hereinafter referred to as E-Azerbaijan earthquake), in northwestern Iran, about 100 km east of Tabriz, the fourth largest city of Iran, with over two million citizens (Figure 1a). The mainshock was recorded by different institutions: the Iranian Seismological Center (IRSC) [2], the United States Geological Survey (USGS) [3], the GFZ-Potsdam (GEOFON) [4] and the Harvard Global CMT catalog [5,6], that furnished four different hypocentral locations and focal mechanisms parameters Despite such different solutions, the analysis of the available focal mechanisms and hypocenters suggests that the E-Azerbaijan earthquake nucleated along a strike-slip fault, located within the complex structural setting of the Bozgush Range [7,8] (Figure 1b,c). One of the strongest historical seismic events took place on 22 March 1879, with Mw 6.7 along the South Bozgush Fault (black star in Figure 1b), causing 2000 casualties and heavy damage to the surrounding villages. The reported data are superimposed on the 1 arcsec Shuttle Radar Topography Mission (SRTM) Digital Elevation Model (DEM) of the zone
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