SOURCE PARAMETER AND B-VALUE ESTIMATION OF LOCAL EARTHQUAKES IN KUMAUN REGION, CENTRAL HIMALAYA, INDIA.

The earthquake activities recorded by establishing 5 stations digital radio frequency network in Kumaun Himalaya has been used to estimate source parameters and b-value; the network stations were equipped with five short period triaxial (L4-3D) seismometers and one accelerometer (CMG-5T) deployed at Nainital. A majority of micro-earthquake events attributed between two major tectonic boundaries viz., the Main Boundary Thrust (MBT) in the South and the Main Central Thrust (MCT) in the North shed new light to understanding the nature of seismicity and their relation with regional tectonics of the region. The source parameters viz., seismic moment, source radius and stress drop of local earthquakes have been computed following Brune’s earthquake source model (1970). The values of seismic moment (Mo), Source radius(r) and stress drop (??) of micro seismic events vary from 7.52E+10 (Nm) to 4.93E+15 (Nm), from 97 m to 620m and between 0.01 bars to 134 bars, where the stress drop found in agreement with the other region of Himalaya. The focal depths of most of the events are shallow foci in occurrence as well as, the depth of these events ranges from 10-25 km, confining above the plane of detachment. The b-value also estimated for the region to define the relative size distribution of earthquake event falling in the area. It was found to be low as 0.59±0.11, interpreted as the region is under the high-stress regime. The spatial distribution of earthquake events between MBT and MCT zones in Kumaun region implies that the region is seismotectonically an active segment of Himalayan fold-and-thrust belt.