# Integrated Earthquake Catalog of the Eastern Sector of the Russian Arctic
## 3 Results
### Merging Catalogs
#### 3.1.3 Stage 3. Merging RUS and Data from the ISC_Other Catalog  
The ISC catalog contains a large amount of data from Russian agencies (Table 2). Accordingly, at this stage of the merging procedure, a large number of duplicates, including absolute ones, are expected.  
When merging, the catalog RUS obtained at _Stage 2_ was taken as the main one and ISC_Other was taken as the additional. The resulting catalog will be designated RUS_ISC. The preliminary analysis of duplicates was performed with the standard distribution parameters \(\sigma_{T}=0.05\) min, \(\sigma_{X}=15\) km, and \(\sigma_{Y}=15\) km (Figure 7).  
More than 10,000 potential duplicates have been identified, about 5000 of which have the same times and/or epicenters. Such pairs represent the same registration of events by the networks of the GS RAS, which are included in the Russian catalogs and the ISC catalog. They were excluded to determine the variances. We have verified that each of the parameters follows a normal distribution and that the mean is small compared to the standard deviation for all three parameters (_DT_, _DX_, and _DY_) (Figure 7). It was also verified that the variance is almost independent of the event magnitude and time. The final analysis of duplicates was performed with the parameters \(\sigma_{T}=0.032\) min, \(\sigma_{X}=12.3\) km, and \(\sigma_{Y}=12.0\) km. We calculated the metric values between events of the RUS catalog. This made it possible to estimate the probability that the duplicate was determined incorrectly due to the high density of earthquakes.  
Figure 7: Distributions of _DT_, _DX_, and _DY_ for the nearest events from the RUS and ISC_Other catalogs, and the dependence of the standard deviations \(\sigma_{T}\), \(\sigma_{X}\), and \(\sigma_{Y}\) and the mean values \(\overline{DT},\ \overline{DX}\), and \(\overline{DY}\) on the time and magnitude of the events. The red dots and bars are the population mean values and standard deviations, respectively.  
We chose the threshold \(Ro=6.0\) (Figure 8). In this case, in addition to 4802 absolute duplicates, another 5706 potential duplicates are identified. Many pairs of earthquakes have the same time or the same coordinates of the epicenter, and 73 of such pairs have large metric values of \(Ro>6\). An analysis of these pairs indicates that the records in the RUS and ISC catalogs differ in one digit. Most likely, these are technical errors of the era of manual information entry, which were corrected when compiling the catalog _Earthquakes of Northern Eurasia_. These events are considered to be duplicates and they are not included in the integrated catalog, despite the large values of the metric.  
Figure 9 shows the spatio-temporal structure of the duplicates in RUS/ISC_Other and the naturally grouped events in the RUS catalog. The metric values for the earthquakes in the RUS catalog are significantly larger than for the RUS/ISC_Other duplicates. The metric level lines \(Ro=6\) and \(Ro=7.6\) provide close-to-optimal separation of the duplicates and naturally grouped events (the lower cluster of black dots). In total, for the studied territory there are 6411 unique events in the ISC_Other catalog. These events have been added to the RUS catalog. The merged catalog RUS_I  
Figure 8: (**a**) Comparison of the metric distribution for RUS/ISC_Other pairs (blue histogram) and the same metric for RUS/RUS earthquakes (red histogram). (**b**) Threshold optimization: the red line is the probability of missing a duplicate in the model with metric (1), the blue line is the probability of a false duplicate, the black line is the total probability of errors of the first and second kind, the dashed line \(Ro=6.0\) corresponds to an equal number of errors of the first and second kind (number of false duplicates is equal to the number of missed duplicates), the estimate of the total number of errors is approximately 0.3%, and the gray bar shows the range of values for the metric \(Ro=6.7\div 7.6\), minimizing the total number of errors (approximately 0.2%).