Spatial distribution of b-value on the Mingachevir water reservoir area for seismicity analysis applying the microzonation method of Babayev G. et. al., 2020.

This research aims to distribute b-value estimation spatially on the Mingachevir water reservoir area, a seismically active zone situated in Azerbaijani part of Kur depression. There are several researches proposing a relation between seismicity and b-value (Babayev G. et. al., 2020, Babayev T. et. al., 2023b, Telesca et. al., 2020). It is shown that, b-value is lower in the high-intensity zones, and higher in the low-intensity zones (Babayev T. et. al., 2023b). b-Value is an important parameter of a linear relation that is called Gutenberg-Richter law. Gutenberg-Richter law represents the earthquakes distribution with respect to the magnitude (Gutenberg and Richter, 1942). The relation below (1) presents Gutenberg-Richter law:

(1) log N = a - bM or N = 10^{a - bM},

where N is the number of earthquakes greater and equal than M, the magnitude of the earthquakes, a and b are the real constants.

 b-Value is the slope of this linear relation, in terms of mathematics. It is a parameter reflecting the relative size distribution of earthquakes (Babayev T. et. al., 2023a). Several ways were improved to estimate b-value (El-Isa, Eaton, 2014). We applied linear least-square fitting method to logarithmically binned data since it is preferred due to its instructivity (El-Isa, Eaton, 2014; Milojevic, 2010). In order to obtain spatial distribution of b-value the microzonation method of Babayev G. et. al., 2020 was applied. By use of this method, the area was divided to the grids of 10 km * 10 km. The seismic events in the Mingachevir catalog were clustered to each grid and b-value was estimated for each grid with the events. The microzonation of the study area was done on ArcGIS 10.7 (ESRI, 2018) software and the mapping of b-value spatial variation was done on SURFER software. According to the result of the research, we observe that mainly, in the study area the b-value has a low quantity, which is proposed to be related with higher seismic activity (Babayev G. et. al., 2020 and Babayev T. et. al., 2023b). Still, it varies through the study area and in the northern part of Mingachevir water reservoir, that is close to Southern Greater Caucasus and in the south-eastern part of the reservoir, that is close to Yevlakh region b-value is around 1. b-variations are impacted by tectonic stress (El-Isa, 2013). Wiemer and Wyss, 1997; Wiemer et. al., 1998; Zuniga and Wyss, 2001; Gerstenberger et. al., 2001; Wiemer and Wyss, 2002; Schorlemmer, 2004; Schorlemmer et. al., 2005; Wyss et. al., 2004; Wyss and Matsumura, 2006; Wyss and Stefansson, 2006 propose b-decrease with the increase of the tectonic stress. The studied area is a depression zone under compression between Lesser and Greater Caucasus mountains. The Kur depression forms a reverse fault or subduction zone by moving under the Greater Caucasus at a rate of 8 mm/year with the stress applied by Lesser Caucasus (Aktug et. al., 2009, 2013; Reilinger et. al., 2006). Therefore, lower b-values and high number of seismic events allow us to consider the relation among b-value, seismicity and tectonic factors.