Time clustering of earthquakes in the SumatraAndaman and Himalayan regions
Increased frequency of earthquakes in the Sumatra–Andaman region in the past 10 years reflects time clustering of earthquakes and does not necessarily imply low recurrence interval of earthquake in the region. Time clustering of earthquakes can occur either due to the stress change (either through static or dynamic stress transfer) caused by the occurrence of a great earthquake in the region, or it could just be a chance in which earthquake occurrence is almost simultaneous in two or more segments, despite differences in the earthquake cycle due to difference in the phase of strain accumulation, rheology, plate convergence rate, etc. in these segments. We note that the Himalaya and the adjoining regions too showed earthquake time clustering during 1897–1950.
http://www.ias.ac.in/currsci/10apr2011/1068.pdf