The b-value and fractal dimension of local seismicity around Koyna Dam (India)

Earthquakes began to occur in Koyna region (India) soon after the filling of Koyna Dam in 1962. In the present study, three datasets 1964-1993, 1993-1995, and 1996-1997 are analyzed to study the b-value and fractal dimension. The b-value is calculated using the GutenbergRichter relationship and fractal dimension Dcorr. using correlation integral method. The estimated b-value and Dcorr. of this region before 1993 are found to be in good agreement with previously reported studies. In the subsequent years after 1995, the b-value shows an increase. The estimated b-values of this region are found within the limits of global average. Also, the pattern of spatial clustering of earthquakes show increase in clustering and migration along the three zones called North-East Zone, South-East Zone (SEZ), and Warna Seismic Zone. The earthquake events having depth B5 km are largely confined to SEZ. After 1993, the Dcorr. shows decrease, implying that earthquake activity gets clustered. This seismic clustering could be helpful for earthquake forecasting. earthquake prediction. Earthquakes are strongly confined to a few regions. Earth's surface is broken into a mosaic of relatively earthquake- free plates, whosemargins releasemore than 99 % of theworld's seismic energy ( Scholz 1990). Sincemost earthquakes occur repeatedly along certain active segments of faults, it is important for long-term prediction to determine their locations and movement of tectonic plate in the past. The spatial and temporal distribution of the past earthquakes of different sizes recorded historically and by seismic networks ( in existence for only about a century), as well as many aspects of earthquake sources and nearsource characteristics, has been studied in attempts to discover some patterns that might be useful for long- to short-term predictions of future earthquakes. Earthquake epicenters can be considered as to be point events in space and time. If the occurrence of each earthquake is totally uncorrelated with other earthquakes then the distribution of events is called Poisson ( random) distribution with well-understood mathematics. In regional seismicity studies, the distributions are not Poisson ( e. g., Knopoff 1964; Singh and Sanford 1972; Smalley et al. 1987). Just as Poisson process is purely random, fractals geometry exhibiting scale-invariant properties such as scale-invariant clustering is applied to study earthquakes. Fractal geometry reveals that simple algorithms can generate complex forms. This describes temporal or spatial properties of geological patterns. It does not describe the mechanism that produces the fractal scaling, but it helps to sort out the possible mechanism or explanation.