Site-specific classical calculations

Starting from version 3.9, the engine offers some optimizations for site specific classical calculations.

Rupture collapsing

If you have multiple sites and you have set the pointsource_distance parameter in the job.ini, then the nodal plane distributions and hypocenter distributions will be collapsed for far away ruptures, as we discussed in the section about common mistakes. If you have a single site, and if you have set in the job.ini the parameter

collapse_level = 1

an additional collapsing will be applied, that will further reduce the effective number of ruptures, even in the case of trivial nodal plane distributions and hypocenter distributions. This additional collapsing takes the ruptures that are more distant than the pointsource_distance from the site of interest, groups them by magnitude and distance, and take only one representative per bin. The number of distance bins is determined by the parameter point_rupture_bins, which has a default of 20, and which can be tuned in the job.ini file. This reduces greatly the number of ruptures at the cost of a minor loss in precision.

By setting collapse_level = 2 one can get even a greater collapsing, which for the moment is left undocumented.

There is a discussion of the mechanism in the MultiPointClassicalPSHA demo. Here we will just show a plot displaying the hazard curve without pointsource_distance (with ID=-2) and with pointsource_distance=200 km (with ID=-1). As you see they are nearly identical but the second calculation is ten times faster.