Predicting the 1975 Haicheng Earthquake

The publicized four-stage (long-term, middle-term, short-term, and imminent) prediction of the M 7.3 1975 Haicheng, China, earthquake once generated worldwide fascination. Yet the prediction process has remained mysterious because of lack of reports on real-time documentation and details of how warnings were issued. In the present work, study of declassified Chinese documents and interviews of key witnesses have allowed us to reconstruct this important history. Our findings indicate that there were two official middle-term predictions but no official short- term prediction. On the day of the earthquake, a county government issued a specific evacuation order, and actual actions taken by provincial scientists and government officials also effectively constituted an imminent prediction. These efforts saved thousands of lives, but the local construction style and time of the earthquake also contributed to minimizing fatalities. Evacuation was extremely uneven across the disaster region, and critical decisions were often made at very local levels. The most important precursor was a foreshock sequence, but other anomalies such as geodetic deformation, changes in groundwater level, color, and chemistry, and peculiar animal behavior also played a role.