What is Epsilon?

TODO need about-deaggregation; check Ex 7 link

What are ε and ε₀?

The ground motion, Y, that might be recorded at a specific site from an earthquake 'source' with a given magnitude and distance is typically modeled as a log-normal variate such that the logarithm of Y, which we denote y, has a normal distribution, with mean, μ, and standard deviation, σ. Epsilon is defined as the standardized y at a site from a specific source: ε = (y – μ) ∕ σ. Because we compute the probability of exceeding some ground motion at a site, p₀, in probabilisitic seismic hazard analysis, our deaggregation tools instead report ε₀ = (y₀ – μ) ∕ σ.