Easy HVSR > Graphics > Stationarity map

Stationarity map

This map is present in the "Selection" and "Spectral analysis" windows. This map shows the H/V spectral ratio of each window. It is, in fact, organized in such a way that along the abscissas axis are present the initial temporal instants of each window, while in the ordinate, the frequencies analyzed. The color map represents, in each point, the spectral width for a given frequency of the H/V spectral ratio associated with a given window selected, according to a color coding.

The usefulness of this graphic is the ability to verify that the H/V spectral ratio of all windows has a homogeneous behavior. In other words, this map should show a trend of the spectral amplitudes constant in time, and thus a thickening of the spectral amplitudes along the same frequencies.

With the help of this graphic the user can choose to discard the windows whose spectral content presents some anomalies compared to the average, which has content of some importance even at frequencies where the other spectral ratios do not show significant values. The presence of these windows does nothing but increase the width of the confidence interval of the final H/V average curve, or it will damage the credibility. This usually takes place at low frequencies, ie below 1 Hz, where the ambient noises are of natural origin and their source is very far in comparison to the sources of anthropogenic origin (much closer) that can easily disturb the contents of the natural sources at low frequency.

To select the spectrum of one of the windows, just click on it, and automatically the corresponding window will be highlighted in the graphics of the traces and in the windows table.