Mapping the b-Value and its Correlation with the Fractal Dimension in the Northeast Region of India

The northeast region of India, one of the most tectonically complex and high seismicity prone regions in the world, is examined with the power law distribution and fractal dimension of seismicity. About 1250 earthquakes (M 2.0 - 5.0) recorded by the permanent stationsltelemetric networks in the region during the period 1993-96 are analysed in this study. The Gutenberg-Richter power law distribution, b-value, is estimated by least square fit and maximum likelihood methods in the five selected tectonic blocks of the region. The b-values (0.5 - 0.9) obtained for the earthquakes (2.5 ≤ M ≤ 5.0) by both the methods are comparable, and it varies with space and depth. The spatial variations of b-value and the activity level ('a' coostant in the power law relation) are mapped. The maps imaged the higher frequency of earthquake occurrence as well as the higher activity level of the seismogenic structures in the region. The fractal dimensions (D) of spatial distribution of earthquakes in the selected tectonic blocks are calculated using the correlation integral. The estimated D values vary from 1.20 to 1.80.