.. _classical-psha-intro:
Classical PSHA
==============
Analysis Input data for the classical *Probabilistic Seismic Hazard Analysis* consist of a PSHA input model provided
together with calculation settings.
The main calculators used to perform this analysis are the following:
1. *Logic Tree Processor*
The Logic Tree Processor (LTP) takes as an input the *Probabilistic Seismic Hazard Analysis* Input Model and creates a
Seismic Source Model. The LTP uses the information in the Initial Seismic Source Models and the Seismic Source Logic
Tree to create a Seismic Source Input Model (i.e. a model describing geometry and activity rates of each source
without any epistemic uncertainty).
Following a procedure similar to the one just described the Logic Tree Processor creates a Ground Motion model (i.e.
a data structure that associates to each tectonic region considered in the calculation a Ground Motion Prediction
Equation).
2. *Earthquake Rupture Forecast Calculator*
The produced Seismic Source Input Model becomes an input information for the Earthquake Rupture Forecast (ERF)
calculator which creates a list earthquake ruptures admitted by the source model, each one characterized by a
probability of occurrence over a specified time span.
3. *Classical PSHA Calculator*
The classical PSHA calculator uses the ERF and the Ground Motion model to compute hazard curves on each site
specified in the calculation settings.
The reader interested in learning more about the science behaind this calculator can explore the
:ref:`Underlying Science ` tab.