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Values of b and p: their variations and relation to physical processes for earthquakes in Japan

Synopsis This work reviews some results obtained already for the variations of the seismicity parameters b and p in different seismogenic and tectonic regions in Japan. We bring as well new evidence that the time and space changes in seismicity parameters are correlating well with the crustal structure and/or some parameters of the earthquake process. In the first part of the paper we show that several seismicity precursors (clear b-value changes, quiescence and clustering) occurred about two years before the 1995 Kobe earthquake and they correlate well with other geophysical premonitory phenomena of the major event. The precursory phenomena occurred in a relatively large area, which corresponds probably with the preparation zone of the future event. In the second part, we analyze the b and p value spatial and temporal distribution for the aftershocks of the 2000 Tottori earthquake. The results indicate significant correlations between the spatio-temporal pattern of b and p and the stress distribution after the main shock, as well as the crustal structure. The swarm-like seismic sequences occurred in 1989, 1990 and 1997 showed significant precursory b and p values. In the third part of the paper we analyze the seismicity during the 1998 Hida Mountain earthquake swarm. The double-differencerelocated events are analyzed for their frequency-magnitude distribution and stress changes. While again the b-value is significantly different in south comparing with the north part of the epicentral area, the physical interpretation is difficult and complex. The changes in the Coulomb failure stress (∆CFF) can explain the b-value distribution features, but the crustal structure may be also important. The seismicity distribution and migration, in relation with ∆CFF is also discussed. We refer as well to other world-wide studies.