Estimation of fractal dimension and b-value of earthquakes in the Himalayan region

Abstract

The Himalayan belt is known for seismic activities; however, activities across this belt are not uniform due to various factors, including stress regime, heterogeneity of subsurface material, and the manner by which the major tectonic Indian plate is colliding with the Eurasian plate. In this study, three sample regions spanning northwest to northeast Himalayas (Kashmir, Nepal, and northeast Himalayan regions) were selected, and their b-values and fractal dimensions from the investigation period of 1973–2015 were calculated. Subsequently, the b-value was calculated via the Gutenberg–Richter relation and maximum likelihood method, whereas the fractal dimension or D-value was calculated using the correlation integral technique. Upon subdividing the time duration into six equal interval subsets, a variation in b-value can be observed over the years. The period 1973–2015 was selected to ensure the sufficiency of data in each subset and an adequate number of subsets for comparisons. From the low b-values, possible high-stress regions and asperities can be inferred, and the variation in stress and heterogeneity of material can be observed from the northwest to northeast Himalayas. An increase in b-value was observed on moving from the northwest to northeast Himalayas during the period of investigation. From the D-value, the extent of the epicentre cluster was observed, revealing that the epicentres were far more clustered to a point in Nepal Himalayas than in the two other regions. The spatial distribution of epicentres was more or less in 1D (fractal dimension) in the northeast and northwest Himalayas, indicating their distribution along particular geological linear features, such as major faults. Hence, a comparative study of the three regions was achieved. On the basis of the b-value, the types of fault and tectonics can be predicted, and the frequency of earthquakes in these Himalayan regions can be better understood.