Application of principal component analysis to some earthquake related data in the Koyna region, India

Bearing in mind the recurrence of earthquakes of magnitude 5.0 in the Koyna region, a new approach based on the principal component analysis has been used to study the distinctive characteristics of September 1967, October 1973 and September 1980 earthquakes. For this purpose, 12 parameters were selected to understand their relative loadings on different principal components. It was found that the first principal component had the largest loadings, due to the number of microearthquakes followed by the dilatations of first motion, at Koyna and Pune observatories for the 1967 and 1980 earthquakes, respectively. The loading due to height of the reservoir and the total seismic energy release was conspicuous, but of a lesser extent for the 1967 earthquake. On the other hand, these two parameters had almost negligible loading for the 1980 earthquake. It was found that the first principal component of the 1973 earthquake had the largest loading due to the height of the reservoir, and the reservoir level change followed by ratio of compression/dilatation. Differences in the mechanism of 1973 and 1980 earthquakes were broadly supported by their seismicity patterns.