Active periods in the world's chief seismic belts

Abstract

The existence of active or inactive periods in the world's chief seismic belts, which is one of the fundamental problems in space—time seismicity, is discussed based on space—time diagrams of the world's large shallow earthquakes in the past seventy-year period. In those seismic belts which correspond to zones of convergence between two large rigid plates, even if the seismic belt is very long, a number of large shallow earthquakes occur in succession throughout the belt within a limited period (the active period). This seismic activity seems to change periodically. Except for the northern circum-Pacific belt, the world's chief seismic belts of this type have nearly common active periods. In other seismic zones, which correspond to triple junctions of rigid plates or complex plate-boundary zones, the space—time distribution of large shallow earthquakes does not show such a regular pattern. The activity of these belts is rather continuous. The present results; suggest that large shallow earthquakes are strongly coupled on a global scale. These global-scale interactions of large shallow earthquakes support the hypothesis of rigidplate tectonics.