Seismicity of the Indian Ocean

The seismicity of the Indian Ocean is primarily confined to the mid-ocean ridge system and its associated rift valley; however, a broad NW-SE band of 29 epicenters is confirmed in the northeastern Indian Ocean—11 of the 29 earthquakes of magnitude 6 or higher. The location of seismic activity on fractures that cut the ridge is shown by the epicenters along the Owen, Prince Edward, and Amsterdam fracture zones and by the epicenters on the fracture at 41°S, 81°E. The seismic activity of the mid-ocean ridge, as shown by the rate of energy release, has been relatively constant since 1922, except for the years 1942 and 1951 when large earthquakes occurred. A solution of the equation Log N = a + b(8 − M), based on data from 76 earthquakes over a period of thirty years, resulted in the values a = −1.78 and b = 0.91 for the mid-ocean ridge system. A table of frequency of occurrence based on this solution shows the frequency of earthquakes to range from fifty years for a magnitude of 8 to one year for a magnitude of 6–6¼.