VARIATION OF b – VALUE IN THE EARTHQUAKE FREQUENCY – MAGNITUDE DISTRIBUTION WITH DEPTH IN THE INTRAPLATE REGIONS

Abstract

We map the earthquake frequency – magnitude distribution ( b value ) as a function o depth in the intraplate regions of the earth. About 590 well – located events in the different intraplate regions are selected for this analysis. The earthquake data sets are separated in 10 km zones from 0 to 40 km depth. The b-value of the intraplate regions ranges from 0.72 to 1.20. There is a clear tendency for decrease in b- value in Africa, Asia, North America and Globally, and increase in b-value in Australia and Europe . The low b-values and low seismicity at depth range of 20-30 km may be associated with low degree of heterogeneity and high rheological strength in the Crust. The result shows that the b-value increases below the depth range of 20-30 km in Africa, Asia, North America and Globally and decreases in Australia and Europe. We found that there is high seismicity below the depth range of 20-30 km. Such high seismicity with high b-values may be associated with high heterogeneity as well as with low strength in the crust.