# 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](../models/index.md) 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.