QUANTITATIVE STUDIES OF GLOBAL SEISMICITY (2)--DISCUSSION ON GLOBAL EARTHQUAKES (M6) FROM 1964 TO 1983

In this paper, the seismicity indexes of global earthquakes (M6) during 1964-1983 are calculated, using data of ISC and USGS. The authors suggest a method suitable for working out a set of regression formulas between mb and Ms. Calculation shows that the seismicity level of global shallow earthquakes during the years of 1964-1965, 1968, 1971, 1975-1976 is higher than normal, and especially more conspicuous is the peak for the years 1975-1976. The year 1984 has taken the place of 1954 in the 20th century as the year of lowest level in global shallow seismicity. According to the actual value of A(b) calculated, the deep seismicity level reaches the highest point in 1971 and drops to the lowest point in 1977. In the time interval of 1977-1983 the global shallow seismicty decreases continuously while the deep seismicity increases with fluctuations.