Answer:
Since 1900 and prior to the December 26 earthquake,
the largest earthquake along the subduction zone from
southern Sumatra to the Andaman Islands occurred in 2000
and had a magnitude of 7.9. A magnitude 8.4 earthquake
occurred in 1797, a magnitude 8.5 in 1861 and a
magnitude 8.7 in 1833 . All three ruptured sections of
the subduction zone to the south of the recent
earthquake. Interestingly, the 1797 and 1833 quakes are
believed to have ruptured roughly the same area with
only 36 years separating the events. Paleoseismic
evidence shows that great earthquakes or earthquake
couplets occur about every 230 years.
