Evaluation of the Seismicity Index for Nigerian Nuclear Installations

Abstract

Seismic Hazard Assessment (SHA) is a quantitative measure of assessing the seismic hazard or risk involved for a given site. The parameter computed for such an assessment is needed for building engineers or national decision makers especially when it concerns nuclear installations. Even though the International Atomic Energy Agency (IAEA) currently makes it mandatory to provide such an index before undertaking any form of development or construction of a nuclear installation, this computation has not been done for Nigeria. Data over long period of time is usually necessary for a quantitative seismic hazard assessment, but because such information is scarce in Nigeria a fractal approach is therefore used in this research. A SHA index called the b-value is evaluated by determining the fractal dimension of the network of locations of recorded past tremor events within Nigeria. In this work a b-value of 0.43 which quantitatively measures the seismic hazard or risk of a given region is computed for Nigeria. Aeromagnetic data was used in producing analytic signal maps that accurately mapped faults that could have been responsible for causing the earth tremors, and the coordinates of these faults or lineament were used in calculating the fractal dimension of the system of faults. The fractal dimension of 0.8568 was obtained by determining the slope of line of best-fit of the plot of the log of the average number of tremor locations <N(R)> within radius R of each location against log of radius R, which was in turn used to determine the b-value. A b-value of 0.43 obtained indicates that Nigeria is in a less seismically active region and this can be used in the IAEA safety guidelines for nuclear installations.