In ShakyGround the models are made up of a series of "sheets". Each sheet is related to a specific item of the model, i. e., the seismic source, the geological structure, the response spectra and the general conditions for the calculus. A further sheet concerns the way how ShakyGround will report the results. We’ve adopted the concept of the sheets in order to provide a safe input, helping to avoid misspellings or the use of incorrect parameters. The sheets can be stored in ShakyGround’s catalog and re-used for the creation of new models.

The first sheet contains the seismic source parameters and its position with respect to the receiver. With the buttons on the right side the users specifies the random fluctuation of the parameters.

The user can re-use a previously defined source clicking the box "Sources in Catalog". ShakyGround allows him to scroll the sources presented in the catalog and to inspect the corresponding source parameters. Otherwise he can specify a new name in the box "Source Name:", enter a new set of parameters, and finally save the new source in the catalog.

The Layer sheet is made up of two levels. In the box "Stratigraphy" one can load an already existing geological model consisting of a number of layers. The user can define a new layer passing to the box "Layer name" or the subsequent ones. Note the buttons on the right side. Similar to the source parameter sheet the user can use these buttons in order to specify the bandwidth of the random fluctuation of the corresponding parameters. Clicking the "Insert" button the new layer can be inserted at any position of the layer stack. An already existing layer can be shifted to any place within the layer stack by clicking it in the box at the bottom and using the "Up" and "Down" buttons.

Of course the new geological model can be saved in the catalog with a new name or overwriting the existing one. Particularly in zonation projects the strategy of using pre-defined stratigraphies is very effective and safe, since the user can recombine with little effort typical geological conditions at the surface and in the structure underneath.

In the response spectrum sheet the user specifies how to calculate the response spectra. Besides the frequency bounds and resolution (see box "Frequencies"), the type of the response spectrum has to be selected (box "Type of Response Spectrum"). The default is set to Acceleration as required by most seismic regulations, but occasionally velocity or displacement response spectra are requested. The default value for the damping is set to 0.05, i. e., 5% of the critical damping. This damping value is usually considered in standard seismic regulations, but occasionally damping values of 1%, 2%, or 10% are requested, too.

The "General" sheet contains basic information about how to perform the calculations. In the box "Seismogram Information" the user must specify the length of the seismogram and the sampling frequency. In the box "Simulation Parameters" the user selects the number of simulations carried out for the model and the seed value for the generator of the pseudo random numbers. Two further items (box "Statistics Source" and "Statistics Layers") concern the mode how ShakyGround varies the model parameters randomly within the ranges selected in the source parameter and layer sheets. ShakyGround allows to vary source and geotechnical parameters according to a uniform or, alternatively, a Gaussian distribution.

ShakyGround allows to place the receiver either at the surface or at some interface within the layer stack. With this option ShakyGround matches the request to consider the case of an edifice whose base is supposed to be situated at some depth. The box on the left schematically displays the geological model. Clicking the an item in this box the user specifies where to place the receiver position. The default, of course, is set to the surface.

Finally, ShakyGround wants to know what the output should look like. By default ShakyGround writes only a general output. If wanted it is possible to see the results of every single simulation selecting 'Write single Time series to disk" and "Write single Response spectra to disk". Often a short output, with a report about calculated signal parameters and response spectra, will be sufficient. Clicking "Write single Time series to disk" each single synthetic seismogram is written to disk and can be visualized at the end of a ShakyGround run. The same holds for the Response spectra. The possibility of inspecting the single time series and response spectra can be used in order to check whether ShakyGround works properly and the choice of the parameters has been suitable. Since the time series and response spectra are written as plane ASCII files it will be easy to transport them to other sophisticated data processing and visualization packages.