The aftershock sequence of the March 1999 Chamoli earthquake (M s 6.6) in the western Himalaya is analysed to examine the seismic characteristics of the active fault. About 350 aftershocks recorded by about 40 seismic stations are used to map the b-value and fractal correlation dimension (D c ) in the earthquake source area. The maximum likelihood method is used to estimate the b-value, and the correlation integral method for the fractal correlation dimension. A comparatively higher b-value (0.7) is mapped to the north at the Main Central Thrust (MCT) zone with respect to a lower b-value (0.5) to the south at the Alakananda fault (ANF) zone. The cross section of the b-value imaged the seismically active ANF at depth. The fractal dimension map, on the other hand, identified the ANF with D c *0.8-0.9, that implies a near linear seismogenic structure at the ANF.