Aftershock Analyses of the Qotur Doublet-Earthquakes on 23 February 2020 in Western-Azarbaijan Province, NW Iran

In determining the mechanism of an earthquake source, two main and auxiliary planes are identified. Proving which plane is really a failure plane has always been of interest to seismologists. Knowledge of these nodal-planes helps a lot to understand the geodynamical model and the stress field in the regional scale. One way to detect the failure plane of an earthquake is to analyze its aftershocks when it has no surface outcrop. In this study, we determine the fracture plane, in other words, the fault causing the Qotur-doublet earthquakes, by analyzing the spatial distribution of aftershocks.The Qotur doublet-earthquakes with magnitudes MN 5.7, 5.9 occurred in 2020 February 23 in western Aarbaijan province near the Iran-Turkey border, and was followed by many aftershocks. We relocated the aftershocks by using the double- difference relocation method (hypoDD). The general pattern of relocated aftershocks distribution shows a seismic zone covering an area of approximately 15×10 km2. The cross-sections through aftershock locations show that the dominant depth range of aftershocks is from ~2 to ~12 km. The results show that the focal depths decrease toward the southeastern part of the region, and deeper-aftershocks are located in the northwestern part. This observation suggests that the causative fault(s) of the Qotur doublet-earthquakes dip toward northwest with striking along the southeast-northwest. According to the mechanism of these double events and their aftershock distribution, the fault causing these events can be a branch of Bahskala fault zone, along the southwest-northeast in the northern part of the Bahskala fault zone.

Aftershock Analyses of the Qotur Doublet-Earthquakes on 23 February 2020 in Western-Azarbaijan Province, NW Iran Keywords:

Qotur , Northwest Iran , Doublet-earthquakes , aftershocks , , relocation , hypoDD