Articles written in Journal of Earth System Science
Volume 116 Issue 3 June 2007 pp 215-223
We analyse the seismicity pattern including 𝑏-value in the north Sumatra–Great Nicobar region from 1976 to 2004. The analysis suggests that there were a number of significant, intermediate and short-term precursors before the magnitude 7.6 earthquake of 2 November 2002. However, they were not found to be so prominent prior to the magnitude 9.0 earthquake of 26 December 2004 though downward migration of activity and a 50-day short-term quiescence was observed before the event. The various precursors identified include post-seismic and intermediate-term quiescence of 13 and 10 years respectively, between the 1976 (magnitude 6.3) and 2002 earthquakes with two years (1990–1991) of increase in background seismicity; renewed seismicity, downward migration of seismic activity and foreshocks in 2002, just before the mainshock. Spatial variation in 𝑏-value with time indicates precursory changes in the form of high 𝑏-value zone near the epicenter preceding the mainshocks of 2004 and 2002 and temporal rise in 𝑏-value in the epicentral area before the 2002 earthquake.
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