Was the 2004 Sumatra-Andaman earthquake the first
mega-event in the region? Seismological data indicate
that earthquakes with M 7.5 and 7.9 occurred in the
Nicobar Islands and an M 7.7 earthquake occurred in the
Andaman Islands in 1941. These past earthquakes
had been considered as the maximum earthquakes in the
Andaman and Nicobar Islands. Instrumental seismological
data are available since the last century. Historical records
of damage from past earthquakes or tsunamis are kept for
more than 1000 years in some countries like China or
Japan. In other places, such historical earthquake
data exist only for less than a few centuries, which may
not be long enough to record the history of large earthquakes.
Geological records such as traces of coastal sea level change or deposits brought by tsunami, called tsunami
deposit, are used to study older earthquakes.
Such a study area is called paleoseismology.