Variability in size and recurrence interval is likely a
characteristic nature of great earthquakes in subduction
zones. Historical and geological data in other subduction
zones indicate that recurrence patterns of past
great earthquakes are highly variable. For
example, in southern Chile, historical records indicate
that past earthquakes occurred in 1575, 1737, 1837 and
1960, with an average recurrence interval of 130 years.
However, the geological evidence or tsunami deposits
were found only from the 1960 and 1575 earthquakes
as well as older earthquakes, yielding the recurrence
interval of ~300 years based on paleoseismological studies.
The 2011 Tohoku earthquake added another example
of such variability.