This refers to a seismic law which states that there is a constant empirical relationship between the frequency of earthquakes in a region and their magnitudes. According to Danish physicist Per Bak who explained the law in his 1996 book, How Nature Works, for every 1,000 earthquakes of magnitude 4, for instance, there are 100 earthquakes of magnitude 5, 10 earthquakes of magnitude 6 and so on. The law has been used to argue that seemingly unpredictable events actually follow a simple pattern. It was formulated by American seismologists Charles Francis Richter and Beno Gutenberg in their 1956 paper, “Magnitude and energy of earthquakes”.