Data Input

The users can start a project typing in its name and, if needed, the customer’s name (see figure 1).

Figure 1. The Project Screen

After saving the data, the project is created and the user can start the data entry. Each project can be made by many different “models”. In SHAKYGROUND, “models” are made up of a series of “sheets”, and each of them is related to a specific item of the model, e.g. the seismic source, the geological structure, the response spectra and the general conditions for the calculus. A further sheet supports the configuration of the results. Such “sheets“ concept has been adopted to provide a safe input, to avoid either misspellings or the use of incorrect parameters. The sheets can be stored in the program catalog and re-used for the creation of new models.
The first sheet focuses on the seismic source parameters and their position with respect to the receiver. The random fluctuation of the parameters may also be specified. The user can re-use a previously defined source by scrolling the sources presented in the catalog (“Sources in Catalog” box) and accessing the corresponding source parameters. Otherwise one 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.

Figure 2. The Source Sheet

The software works together with Google Earth to allow for an easy location of an earthquake. The map of the event is presented in a browser screen on the right hand part of the “Source Sheet” window.

Figure 3. The Strata Sheet

The “Strata” sheet (Figure 3) is made up of two levels. In the box “Stratigraphy” one can select an already existing geological model consisting of a number of layers. The user can define a new layer by using the box “Layer name” or the table below. A already explained for the source parameter sheet, the user can here specify the random fluctuation of the layer parameters. By clicking on the “Insert” button, the new layer is inserted in the layer stack. Any layers can be moved within the layer stack by selecting it in the box at the bottom and using the “Up” and “Down” buttons.

The created geological model can be saved in the catalog with a new name or overwriting an existing one. For zoning projects, the strategy of using pre-defined stratigraphies is particularly effective and safe, since with little effort the user can recombine typical geological conditions at the surface and in the structure underneath.

SHAKYGROUND allows to place the receiver either at the surface or at some interface within the layer stack. With this option the tool allows analysing the case of a building whose base is supposed to be situated at some depth. The default position is set at the ground surface.

The “Additional Data” sheet (Figure 4) contains three different areas: Response Spectrum, General and Output.

Figure 4. The “Additional Data” Sheet

In the “response spectrum” section the user can specify some settings used by the model for calculating the response spectra (type of the response spectrum, frequency bounds and resolution). The default response spectrum is “Acceleration” as required by most seismic regulations, but when needed velocity or displacement response spectra can be selected. 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% have also to be used.

The “General” section of the 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 the program varies the model parameters randomly within the ranges selected in the source parameter and layer sheets. It is possible to configure the model to calculate source and geotechnical parameters according to a uniform or a Gaussian distribution.

The “Output” section is used to specify how SHAKYGROUND should handle the output. Usually a short output, with a report about calculated signal parameters and response spectra, is sufficient. By ticking on “Write single Time series to disk”, the program is configures to write each single synthetic seismogram is on the computer hard disk: such dataset and can be visualized at the end of the run. The same applies for the Response spectra. These features enable the user to access the single time series and response spectra, thus verifying the good choice of the parameters and the performances of the model. Since the time series and response spectra are recorded as plane ASCII files, they can be easily imported by other sophisticated data processing and visualization packages.

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