inparam.source.yaml

time axis

time_axis:
    record_length: 1800.
    enforced_dt: NONE
    Courant_number: 1.0
    integrator: NEWMARK

The default courant_number of 1.0 is very unlikely to be stable: start with something like 0.6 and increase once you know it is working.

*** What is the units of record_length?

---

sources

list_of_sources:
    - VIRGINIA_201108231751A:
        location:
            latitude_longitude: [37.91, -77.93]
            depth: 12e3
            ellipticity: true
            depth_below_solid_surface: true
            undulated_geometry: true
        mechanism:
            type: MOMENT_TENSOR
            data: [4.71e24, 3.81e22, -4.74e24, 3.99e23, -8.05e23, -1.23e24]
            unit: 1e-7
        source_time_function:
            class_name: GaussianSTF
            half_duration: 50.
            decay_factor: 1.628
            time_shift: 0.
            use_derivative_integral: ERF
            ascii_data_file: stf.txt
            padding: FIRST_LAST
            nc_var_times
            nc_var_data: stf_data
            padding: FIRST_LAST
            chunk_size: NONE

The key that you use, e.g., VIRGINIA_201108231751A is arbitrary. We normally use the CMT Catalogue designator for the earthquake in question.

We recommend sticking to specifying the location using latitude_longitude, remembering that north and east are positive and depth is in metres – this is important!

The ellipticity correction is easy to change and makes little difference unless you need very exact arrival times.

We will come back to depth_below_solid_surface and undulated_geometry in the 3D models section.

You are most likely to use the mechanism: type: MOMENT_TENSOR, in which case you should input the data as the components of the moment tensor in the order given by CMTSOLUTION. Remember that CMT uses the non-SI unit of dyne-cm, so you need to add a correction factor by setting unit to 1e-7 to turn this into N-m.

For most purposes (seismogram generation), you can do everything involving the source-time function (STF) after the simulation is complete in post-processing. In this case, set half_duration to 0.0 and the code will make the width of the STF something like 5x’s the timestep (much less than the mesh period, i.e. a delta function). Note that in a model like this, this is as good as you are going to get – the half-duration cannot be exactly 0.00000, but the difference is miniscule and irrelevant.

Leave class_name as GaussianSTF and use_derivative_integral as either ERF or GAUSSIAN depending on whether you want displacement or velocity output. We will come back to how to process the output in a later section.

If you are doing something like wavefield visualisation, then you need to set the STF before you do the simulation. In that case, you can set the half-duration and decay factor as you want, or use netcdf_STF or STREAM_STF (NetCDF vs. ASCII - more on this later) to read in a particular source-time function that you want to use, for example one downloaded from SCARDEC.

A general note of caution: although you can use any STF you want for seismogram generation, and then deconvolve it out before reconvolving with a new STF, we find that this is rarely a sensible option as it ends up producing numerical artefacts. If you are not sure what STF to use, use a delta function (as described above) and deal with it later.