GLOBAL VARIATION OF SEISMIC ACTIVITY

The global variation in the space-time distribution of great shallow earthquakes is examined using the surface-wave magnitude M and the magnitude Mω obtained from the seismic moment. In the past several decades, the seismic activity was complementary in the regions of low latitude (<40° ) and high latitude (>40° ). During the roughly twentyyear period around 1960, the seismic activity was very high in the high-latitude regions and appreciably low in the low-latitude regions. In particular, it is pointed out that the greatest earthquakes occurred roughly simultaneously in the north and south regions of high latitude around 1960. However, the present time seems to be an active period in the low-latitude regions. These regions account for the larger part of the earth's surface, and sustain a degree of destruction and loss of life that is far out of proportion with the relative energy release in the low and high latitude regions. © 1979.