For the Poisson model the addition of fault sources to the smoothed seismicity raises the hazard by 50% at locations where the smoothed seismicity contributes the highest hazard and up to 100% at locations where the hazard from smoothed seismicity is low. For the strongest aperiodicity parameter (smallest α), the hazard may further increase 60%–80% or more or may decrease by as much as 20% depending on the recency of the last event on the fault that dominates the hazard at a given site.
What is the effect of Time-Dependent Source Model using Brownian passage time recurrence model on the Probabilistic Seismic Hazard?.
Various statistical models have been proposed for the computation of the probability
density function for earthquake recurrence, such as Gaussian, log-normal, Weibull, Gamma, and Brownian Probability Time-dependent model (BPT).
The Poisson model is standard practice for most probabilistic seismic-hazard analyses. The BPT model requires a minimum of two parameters as well as knowledge of the time of the most recent rupture. One parameter is the mean-recurrence interval, μ, and the other describes the variability of recurrence intervals and can be related to the variance of the distribution. This variability of recurrence intervals is described as the aperiodicity, α, which is related to the mean divided by the standard deviation.
The behavior of a BPT model depends strongly on the value of α. For smaller values of α, fBPT(t) is more periodic, is strongly peaked, and remains close to zero longer. For larger values, the time in which the earthquake is very unlikely, the delay or dead time, becomes shorter, and fBPT(t) becomes increasingly Poisson like. The hazard function increases with decreasing values of α and becomes Poisson like with increasing values that approach 1.0.
In general, as α decreases (periodicity increases), the deaggregation indicates that the hazard is highest near faults with the highest earthquakes rates. This effect is strongest for the long-period (1 sec) ground motions.
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