Earthquake probabilities
Spreadsheet to calculate the conditional probability of
an earthquake given the date of the last earthquake, a time window,
and the assumed mean and standard deviation of recurrence times.
A range of probabilities comes out of using
three simple commonly used models:
1) Assuming that the recurrence of large earthquakes
are described by a time-independent Poisson process, such that
a future earthquake is equally likely immediately after the past one
and much later. The probability that an earthquake will occur in
the next t years is approximately t/T, where T is the
assumed mean recurrence time.
Because Poisson processes have no "memory," this model assumes
that a future earthquake is equally likely immediately after one occurs
and much later.
2) Assuming time-dependent models in which
a probability distribution describes
the time between earthquakes. In such models the conditional probability
of the next large earthquake, given that it has not yet happened, varies
with time. The probability is small shortly
after the past one, and then increases with time. The spreadsheet
assumes the the recurrence times are described by either
a Gaussian or lognormal distribution with a specified mean
and standard deviation.
For an example of the effect of different models and
parameters on the estimated probability of large
earthquakes in the New Madrid seismic zone
click here