# Advanced Unified Earthquake Catalog for North East India
## 6 The Magnitude of Completeness (M\({}_{\rm c}\))  
Dechustered earthquake catalogs for the periods 1737-1963, 1964-1990, 1964-2000, and 1964-2012 have been studied to distinguish temporal differences in earthquake happenings in NE India. Four graphs, corresponding to four different periods, have been plotted to show the relationships between various bin of magnitudes and the corresponding cumulative number of events having an earthquake magnitude greater than the corresponding magnitude of completeness (Figure 17).  
The Magnitude of Completeness M\({}_{\rm c}\) has been calculated by the EMR method [37] for various catalog times using the ZMAP program. M\({}_{\rm c}\) values are seen to decline with the introduction of the newest information throughout time (Table 4). As the detection threshold for the sample area increased from 1964 onwards, the general trend of the 'b' value continuously decreased over time, resulting in the recording of a greater number of smaller magnitude earthquakes in proportion to large magnitude occurrences, as seen in Table 4.  
Figure 16: Aftershocks are removed using magnitude-dependent spatial and temporal frames (dependent occurrences). The asterisks under the window lines are interpreted as dependent occurrences.  
In the M\({}_{\rm w}\) catalog, the EMR approach is used to determine M\({}_{\rm c}\) for various catalog time periods using the ZMAP application. M\({}_{\rm c}\) values are decreasing w.r.t increasing time periods. From 1964 onwards, the detection threshold for the sample region is constantly grown over time, resulting in the recording of a higher number of lower magnitude earthquakes to big magnitude events. The value of M\({}_{\rm c}\) for the M\({}_{\rm w}\) catalog is more than the M\({}_{\rm wg}\) catalog (Table 5). This shows that more earthquakes within a certain region are more complete on the M\({}_{\rm wg}\) scale than the M\({}_{\rm w}\) scale (Table 5).  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Catalog Time Periods** & **M\({}_{\rm c}\)** & **b** & **a** \\ \hline
1737–1963 & 5.6 \(\pm\) 0.23 & 0.74 & 6.5 \\ \hline
1964–1990 & 4.1 \(\pm\) 0.17 & 0.98 & 7.56 \\ \hline
1964–2000 & 4 \(\pm\) 0.17 & 0.85 & 6.86 \\ \hline
1964–2012 & 3.9 \(\pm\) 0.23 & 0.81 & 6.83 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Estimated Mc, ’b,’ and ’a’ values for various catalogs.  
Figure 17: Four different plots showing the cumulative number of earthquake events vs. magnitudes greater than the corresponding magnitude for the following catalog time periods (**a**) 1737–1963, (**b**) 1964–1990, (**c**) 1964–2000, and (**d**) 1964–2012. In addition, these plots show M\({}_{\rm c}\) values determined by the EMR technique.  
Furthermore, the magnitudes of 'M\({}_{\rm c}\)', 'b,' and 'a' values for all the nine seismogenic zones have been determined. Only data on occurrences from 1964 to 2012 are used to calculate M\({}_{\rm c}\) values for distinct seismic zones, while the whole catalog for the period 1737-2012 is used for the estimate of 'b' and 'a' values. Table 6 displays the seismicity parameters for the various seismogenic zones.