STRANGE ATTRACTOR CHARACTERISTICS OF EARTHQUAKES IN SHILLONG PLATEAU AND ADJOINING REGIONS

Strange attractor dimensions were determined for two concentric areas of about 220 km (2 degrees) and 440 km (4 degrees) radii around WWSSN station at Shillong based on earthquake data during the period 1964 to 1992. Existence of deterministic chaos for both the areas was support ed by the same fractal dimension of 6.1 and positive value of the larg est Lyapunov exponent. The results have provided justification for del ineating precursory seismicity patterns based on earthquakes up to epi central distance of 440 km on different fault systems. Conspicuous hig her value of the strange attractor dimension in Hindukush, Himalaya an d northeast India than that in Koyna region in the peninsular India su ggests a new criteria for distinction between interplate and intraplat e earthquakes. Differences with subduction zone in Pacific vis-a-vis s tress drop in great earthquakes (M greater than or equal to 8) and imp lications of the chaotic approach in earthquake hazard analysis have a lso been brought out.