UCERF3 ERFs Available in OpenSHA

UCERF3 is a complex model comprised of many logic tree branches. Multiple ERFs are implemented in OpenSHA allowing users to access either a single logic tree branch or a mean model. This page describes the different ERFs available and their uses/caveats.

Fault System Solution ERF

Class name: scratch.UCERF3.erf.FaultSystemSolutionERF

This is the base class of all UCERF3 related ERFs, although it is also applicable to any FaultSystemSolution. It allows you to browse for a solution zip file, such as the branch averaged fault system solutions explained below

Branch Averaged Fault System Solutions

These solutions are an approximate mean model for a single Fault Model. Each rupture rate, magnitude, and rate is the weighted mean of all 720 time independent logic tree branches for that Fault Model. This means that magnitude and rake variability is discarded for a single mean value. Additionally, fault geometries can vary between logic tree branches due to aseismicity factors - this solution uses aseismicity factors derived from branch averaged slip rates. They are useful for quick calculations, but can vary substantially from the true model especially near dipping faults with variable aseismicity among logic tree branches.

Time independent hazard curves calculated with these solutions will differ from true mean (curves that were calculated for each logic tree branch independently then averaged) by 0-7%. Gridded seismicity contained in these solutions is weight averaged and captures the true mean perfectly.

They can be downloaded here:

• Fault Model 3.1: ​http://opensha.usc.edu/ftp/kmilner/ucerf3/2013_05_10-ucerf3p3-production-10runs/2013_05_10-ucerf3p3-production-10runs_COMPOUND_SOL_FM3_1_MEAN_BRANCH_AVG_SOL.zip
• Fault Model 3.2: ​http://opensha.usc.edu/ftp/kmilner/ucerf3/2013_05_10-ucerf3p3-production-10runs/2013_05_10-ucerf3p3-production-10runs_COMPOUND_SOL_FM3_2_MEAN_BRANCH_AVG_SOL.zip

UCERF3 Single Branch ERF

Class name: scratch.UCERF3.erf.UCERF3_CompoundSol_ERF

This ERF allows you to select a single logic tree branch from the 1440 time independent UCERF3 logic tree branches for calculations. It will download the full UCERF3 compound fault system solution which contains results from each individual logic tree branch (described here, can be downloaded ​here). This can take some time (as it is an 810 MB file), so the file is cached in "~/.opensha/ucerf3_erf" where "~/" is the users home directory. This location can be changed by setting the "uc3.store" property at runtime.

MeanUCERF3 ERF

Class name: scratch.UCERF3.erf.mean.MeanUCERF3

This is a full "true mean" fault system solution. It is similar to the branch averaged fault system solution described above, but instead uses duplicate versions of each rupture whenever a key property (rake, magnitude, area) changes. This retains all variability allowing for quick reproduction of mean UCERF3 results with a minimum set of ruptures. It also allows for the user to, optionally, apply certain approximations to reduce the rupture count (and thus hazard curve compute time) at the expense of accuracy. These approximations are described below:

Upper Depth Tolerance

Some sections have varying upper depths on different branches due to variable aseismicity values. This parameter combines upper depths within the given tolerance to reduce the subsection (and thus rupture) count. The "Use Mean Upper Depth" parameter allows you to use the average upper depth (default uses the shallower depth).

Note with time dependence: Time dependent UCERF3 is incompatible certain settings of this parameter. It must be set sufficiently high (e.g. 10 km) in order to prevent multiple instances of a subsection (and thus incorrect recurrence intervals).