Abstract
A damaging earthquake of Mw 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. Astatistical 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.
Highlights
The destructive Bhuj earthquake of Mw 7.7 on January 26, 2001, which ravaged through the Kachchh and adjoining regions of India, caused a death toll of 30 000 and loss of property worth more than 10 million US dollars (Gupta et al, 2001)
The ground motion data of the aftershock sequence of this Bhuj earthquake were recorded at Gauribidanur Seismic Array Station (GBA)
The fourier amplitude and phase spectrum of this deterministic signal are shown in fig. 10 as traces ‘b’ and ‘c’ respectively
Summary
The destructive Bhuj earthquake of Mw 7.7 on January 26, 2001, which ravaged through the Kachchh and adjoining regions of India, caused a death toll of 30 000 and loss of property worth more than 10 million US dollars (Gupta et al, 2001). The India Metrological Department (IMD) gave the epicentre of this earthquake as 23.40N and 70.28E with focal. The aftershocks following this major earthquake were recorded at GBA, India, at distance of around 1300 km from the epicentre. The layout of seismometers at GBA station is given in the in-set of fig. 1. In this paper the temporal behavior of the aftershocks in the initial 144 h is analysed
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