Foreshocks and earthquake prediction

Abstract

If a group of foreshocks can be distinguished from ordinary seismic activities, it would contribute to earthquake prediction. In the case of two Japanese earthquakes, which were preceded by immediate foreshocks, the coefficient “ b” in the magnitude versus frequency equation was significantly smaller than that of the aftershocks or of the ordinary seismic activity in the region. The same characteristics were also found for the Chilean earthquake of 1960. Very large earthquakes can also take place without any immediate foreshocks. The great Kanto earthquake of 1923 was not preceded by any immediate foreshocks. However, the seismic activity in the general region became abnormally high from one year prior to the earthquake. Whether large earthquakes in a specific region are preceded by foreshocks or not, or, if not, what kind of foregoing activity is noticeable may probably vary from one seismic region to another. Therefore, detailed seismic data over a long period of time will be necessary to know the regional characteristic of foreshocks or foregoing activity. To achieve earthquake prediction, the physical process of accumulation and release of seismic energy must eventually be made known as well as statistical data.