Variations of b-values preceding large earthquakes in the Andaman-Sumatra subduction zone

摘要

Fifteen largest earthquakes, M_w ≥ 7, occurring between 2000 and 2010 in the Andaman-Sumatra region are studied. The available USGS list of events used is complete for a threshold magnitude M_c = 4.5 and contains 6973 shocks. Spatial and temporal variation of b-values, in the Gutenberg-Richter formula log N = a - bM, was investigated in six selected epicentral regions. The technique of moving spatial- and time-windows was applied. Deduced b-values show large variations from 0.55 to 2.40. The 15 largest events all took place within regions of low b and were preceded by significant drops in b-values. Observed correspondence between low b and the occurrence of large earthquakes suggests that b{t) has a potential which could be employed in a medium term (months, years) earthquake prediction.