Variation of regional Gutenberg-Richter law parameter before and after large earthquakes in some earthquake prone zones around the world

This paper presents variation of Gutenberg-Richter law parameter b for epicentral regions of large earthquakes in different earthquake prone areas in the world like Japan, California, Sichuan province (China), North-Eastern India, Maule (Chile), L'Aquila (Italy), Off-west-coast of New Zealand, Sumatra (2004 tsunami region) from both clustered and de-clustered catalogs. A decreasing trend of b before major earthquakes is observed in most cases and after a large event the b value shows an increasing trend. It is shown that the variation of b for foreshock and aftershock of a large event in a region also follows the same trend. (author)