The oscillatory behaviour of the aftershocks rate of the 2001 Bhuj earthquake, India: observation and interpretation

A damaging earthquake of M-w 7.7, which struck the Bhuj region of India on January 26, 2001, was followed by a large number of aftershocks. The aftershock data available at Gauribidanur Seismic Array Station (GBA), India, till 869 h following the main shock were compiled. The plot of the aftershocks rate with time was found to be oscillatory decay. There was a sharp decrease of the aftershocks rate in the initial 144 h from the main shock and this paper presents the analysis of the temporal characteristics of aftershock activity during this period. A statistical best fit for the rate of aftershocks is performed using the generalised Omori's law and the exponential decay law. The statistical errors for the exponential fit are found to be lower than that of the generalised Omori's fit. The superimposed oscillations present in the aftershock activity are extracted by differencing the observed aftershock activity from the statistical fits. The frequencies of these oscillations are found to be 0.062 h(-1), 0.078 h(-1), 0.102 h(-1), 0.118 h(-1), 0.141 h(-1), 0.164 h(-1), 0.233 h(-1) and 0.476 h(-1). Some of the plausible causes for this kind of oscillations present in the aftershock activity are also discussed in this, paper.