This is a modification of gmsim_v16.1.1 based on developments during the work of Robin Lee in 2017/2018. This is the version used in Lee et al. (2019):
Using an LF Vs30ref that is based on the Vs value of the ground surface grid point in the 3D velocity model as opposed to a constant value of 500m/s.
This change was implemented to ensure that the LF simulation (emod3d) outputs had the correct and consistent CB14 amplification applied to it.
Background
Due to limitations of the 3D velocity models used, the LF simulation results are not usually output at reference velocities which are equal to the true site velocities. This is the reason empirical CB14 site amplification is used ( in addition to accounting for nonlinear effects in soft soils). However, the reference velocity used previously was always 500m/s (corresponding to a basin site within a velocity model with a minimum velocity of 500m/s enforced). When rock sites are present, their reference velocities in the LF simulations from the 3D velocity model are usually above 500m/s, hence the use of a constant 500m/s is not necessarily appropriate. Therefore the Vs30ref values that should be used are at the ground surface grid points in the 3D velocity model where the waveforms are output.
Computational Implementation
The Binary Workflow that is currently used extracts these values from the corresponding 3D velocity model using the numpy memmap function.
The default (no arg) behavior is to use Vs30ref from the 3D velocity model.
Therefore the root_defaults.yaml file should look like the following for a 100m grid run, with no lfvsref set:
If you wanted to use lfvsref: 500.0 (or any other constant value) then it must be added under the bb heading in the version's root_defaults.yaml file. This would correspond to gmsim_v16.1.1.