Probabilities of future earthquakes can be estimated
from past earthquake data. Earthquake probabilities in a
certain time window, for example in the next 30 years,
can be calculated by fitting inter-earthquake times with
a probabilistic density function. If earthquakes occur
randomly in time, or a fault does not have any memory
of past earthquakes, the Poisson process is assumed to
compute the time-independent probabilities; i.e., the
probability of the next earthquake is constant through
time, depending solely on the average recurrence interval.
Alternatively, earthquake probabilities may increase
with time, if similar size earthquakes recur more or less
regularly (called characteristic earthquakes). The elastic
rebound theory explains that an earthquake occurs when
the accumulated stress at the plate boundary reaches
certain limit. In such a case, statistical distributions such
as log-normal distribution or Brownian passage model
, with the average recurrence interval and the
date of most recent events, are used to calculate the
time-dependent probabilities.