# Temporal occurrence models¶

Module `openquake.hazardlib.tom` contains implementations of probability density functions for earthquake temporal occurrence modeling.

class `openquake.hazardlib.tom.``PoissonTOM`(time_span)[source]

Poissonian temporal occurrence model.

Parameters: time_span – The time interval of interest, in years. ValueError – If `time_span` is not positive.
`get_probability_no_exceedance`(occurrence_rate, poes)[source]

Compute and return, for a number of ground motion levels and sites, the probability that a rupture with annual occurrence rate given by `occurrence_rate` and able to cause ground motion values higher than a given level at a site with probability `poes`, does not cause any exceedance in the time window specified by the `time_span` parameter given in the constructor.

The probability is computed using the following formula

```(1 - e ** (-occurrence_rate * time_span)) ** poes
```
Parameters: occurrence_rate – The average number of events per year. poes – 2D numpy array containing conditional probabilities the the a rupture occurrence causes a ground shaking value exceeding a ground motion level at a site. First dimension represent sites, second dimension intensity measure levels. `poes` can be obtained calling the `method`. 2D numpy array containing probabilities of no exceedance. First dimension represents sites, second dimensions intensity measure levels.
`get_probability_one_occurrence`(occurrence_rate)[source]

Calculate and return the probability of event to occur once within the time range defined by the constructor’s `time_span` parameter value.

`get_probability_one_or_more_occurrences`(occurrence_rate)[source]

Calculate and return the probability of event to happen one or more times within the time range defined by constructor’s `time_span` parameter value.

Calculates probability as `1 - e ** (-occurrence_rate*time_span)`.

Parameters: occurrence_rate – The average number of events per year. Float value between 0 and 1 inclusive.
`sample_number_of_occurrences`(occurrence_rate)[source]

Draw a random sample from the distribution and return a number of events to occur.

Method uses numpy random generator, which needs to be seeded outside of this method in order to get reproducible results.

Parameters: occurrence_rate – The average number of events per year. Sampled integer number of events to occur within model’s time span.