Earthquake Prediction and Warning

Abstract

A destructive earthquake of magnitude 7.3, occurring near Haicheng, Liaoning Province, China on 4 February 1975, was forecast successfully. Many lives were saved by an evacuation warning issued several hours prior to its occurrence. By contrast, another earthquake of magnitude 7.5, hitting the Tangshan area, Hopei Province on 28 July 1976, does not seem to have been predicted. It is believed that many thousands of lives were lost there although no official announcement was ever made about the damage or loss of life. These two Chinese earthquake indicate exactly the present status of prediction. Pre-earthquake indicators are manifold; they are land deformation, seismic activity, seismic wave velocity, changes in geomagnetic and geoelectric fields a well as variations in earth resistivity, gravity, underground water and so forth. Monitoring and analysis of precursory indicators have led us to conclude that there are at least two kinds. The logarithmic time of a long-term precursor is proportional to the magnitude of main shock. It amounts to seven-eight years for a magnitude 7 earthquake and 40–50 days for a magnitude 5 earthquake. Furthermore, indicators having a precursor time of several hours can sometimes be observed. Combining these precur or with periodicity of large shock a apparent from historical record and the accumulation of crustal strain as monitored by repeated geodetic surveys, allows a certain degree of earthquake prediction. These indicators seem to be supplemented by geophysical precursors of another kind and by specific anomalous animal behaviour. Even when a fairly accurate prediction of a damaging earthquake can be achieved, it will be no easy matter to issue a warning to the public because of the anticipated social unrest. Economic loss due to a warning may even exceed the damage caused by the earthquake itself, although many lives will certainly be saved by an accurate prediction.