Understanding the Variation of Seismicity in the Eastern Himalayas:
Using Earthquake Frequency-Magnitude Distribution and Fractal Dimension
Abstract
The Eastern Himalayan region, along with its neighboring area is known
to be the part of the ‘Alpine-Himalayan global seismic belt’, a
seismically active area of the world. In the past (1897, 1905, 1934, and
1950) four great earthquakes have triggered in this region with a
magnitude higher than Mw=8.0. The 2011
(Mw= 6.9) Sikkim and 2015 (Mw= 7.8)
Gorkha Nepal earthquakes call attention to the need for a more accurate
understanding of seismic characteristics in the Eastern Himalayan
region. In the present study, analysis of spatial variation of seismic
activity in the Eastern Himalayas and its surroundings is done by
analyzing the variation of seismic parameters and fractal dimension
(Dc). Considering the seismicity data and tectonic
features, the eastern part of the Himalayas is divided into eight
seismic source zones. For the comparison of the seismicity between each
seismic source zone, seismic parameters like average seismic activity
rate at threshold magnitude (λo), maximum possible
earthquake magnitude (Mmax), and ‘b-value’ are
calculated. Seismic parameters of seismic zones are calculated by
considering the incompleteness of earthquake catalogue, for that
sub-catalogue is prepared for each seismic zone, which is complete to
the different threshold of magnitude. The seismotectonic stress
variations in Eastern Himalayas are indicated by the estimated values of
b and Dc. The calculated seismic parameters can be used
directly for seismic hazard analysis of the study area. Keywords:Eastern
Himalayas; Seismicity; Fractal dimension; Seismic source zone