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Abstract: We study the frequency-magnitude relationship for earthquakes in the North-eastern (NE) region of India (Eastern Himalayan zone (EHZ) and Indo-Burman convergence (IBCZ) plate boundary system) using the Gutenberg-Richter relationship given as: log N(M)=a-bM (where N is the number of event with magnitude ≥M and a, b are constants). We have also compared our results with the global data set. In our analysis we use earthquakes of magnitude (m_b)>4, recorded between 2001 and 2014, by the Northeast Telemetered Network and the global networks of ISC, USGS and IRIS. Our analysis is done as a two-step process: (a) estimation of the moment magnitude (M_w ) of the earthquake by fitting the P-wave source spectra using a circular fault model; and (b) linear regression to the distribution of frequency of earthquakes within given ranges of moment magnitude using the Gutenberg-Richter relationship. The magnitude of completeness for the set of earthquakes used in our study was found to be (M_w ) 4.5. Accordingly, the range of earthquake magnitude was chosen to be in increments of 0.5 between (M_w ) 4.5 and 7.0. We study the b-value for both interval and cumulative frequency of earthquakes. Our estimated b-value in northeast region of India for the entire dataset is 0.70 (cumulative) and 0.91 (interval) for the periods 2001-2014, where the b-values for whole Earth in the same periods have estimated as 1.08 ± 0.02 (cumulative) and 0.98 ± 0.01 (interval). We observe a distinctive variation in the b-value for plate boundary and intra-plate earthquakes. We sub-divided the region in three zones and estimated the b-values: (i) EHZ with b-values of 0.90 (interval) and 1.07 (cumulative); (ii) IBCZ with b-values of 0.50 (interval) and 0.75 (cumulative); (iii) NE-India (including the Shillong Plateau and Bengal Basin (SPBB)) with b-values of 0.70 (interval) and 0.90 (cumulative). We also explore possible relationship between cumulative b-value and interval b-value in northeast India as well as whole Earth.
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