Space time clustering properties of seismicity in the Garhwal-Kumaun Himalaya, India

The earthquake data of Garhwal-Kumaun Himalaya from 2007-2013 have been used to study the spatio-temporal behaviour of seismicity. The b-value analysis under Entire Magnitude Range (EMR) method has been adopted to study spatio-temporal behaviour of seismicity. The fractal dimension (D-c) for the seismicity of the region has been calculated using correlation integral method. The maximum likelihood estimates for whole region provides the b-value as 1.05 +/- 0.05. A significant spatial variation is observed in b-value for Garhwal region, where the value varies in three different spatial domains as 1.42 +/- 0.2, 0.97 +/- 0.08 and 1.17 +/- 0.13 from the northwest Garhwal towards the Kumaun region. An increase is observed in the temporal b-value after the Kharsali earthquake of 22nd July 2007, after which there is a significant lowering of the earthquake magnitude levels in the region. This was subsequently followed by a sudden fall in b-value. The temporal analysis of b-value indicates a significant decrease in b-value in 2009. The b-value decreases from 1.3 +/- 0.1 to 0.86 +/- 0.08 for the period of July 2007 to August 2010 and September 2010 to November 2013, respectively. The correlation integral analysis indicates a straight portion observed in the range between 12.39-45.65 km with fractal dimension D-c= 1.53 +/- 0.04. The observation from correlation integral analysis indicates the presence of a space-time clustering in the area of investigation. The inferences based on spatial and temporal variation in b-value indicate a relative increase in recent seismic activity in the regionA (northwest Garhwal) and C (Kumaun) compared to the region B (southeast Garhwal) with low b-value due to decrease in the number of small magnitude earthquakes probably indicate accumulation of high stresses in the region.