Seismicity pattern in north Sumatra-Great Nicobar region: In search of precursor for the 26 December 2004 earthquake |
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| Authors: | Sujit Dasgupta Basab Mukhopadhyay Auditeya Bhattacharya |
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| Institution: | (1) Geological Survey of India, 27 Jawaharlal Nehru Road, Kolkata, 700 016, India |
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| Abstract: | 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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| Keywords: | Seismicity seismic quiescence b-value foreshocks Sumatra-Great Nicobar region |
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