abstract

On August 16, 22, and 23, 1976, a succession of three large earthquakes (M = 7.2, 6.8, 7.2) occurred in the Sungpan-Pingwu area of Szechuan Province, People's Republic of China. Their successful predictions resulted in a substantial reduction in the loss of lives. The epicenters of these events progressed from north to south along the Huya Fault, a NNW-striking fault between the NE-trending Lungmenshan fracture zone and the north-trending Mienchiang fracture zone in western Szechuan. The greatest intensity reported was IX; isoseismals were crudely elliptical with the long axis parallel to the trend of the Huya Fault. The predictions were made with a reasonably good magnitude window (less than 0.5 magnitude unit), a rather large space window (about 150 km × 150 km), and a remarkably good time window (within a day). The detailed prediction process began with field monitoring some 6 yr before the Sungpan-Pingwu events and ended with the final issuance of warning and mass evacuation.

During the few weeks preceding the earthquakes, about 1,300 observations of noninstrumental anomalies and precursory phenomena were reported by scientists and lay brigades: outgassings, fireballs and other earthquake lights, abnormal animal and plant behavior, and telluric currents.

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