7.1.4 H/V computation and output format

Frequency Domain

H/V computation

To start the H/V computation you must have load a 3-components signal in the signal viewer and define the processing parameters under the H/V tool box (see the processing parameters and windowing sections). You can also load the processing parameters from a log file (click on the "Load parameters" button and select the log file from the browser). Once you have done it, click on the "Start" button. The time computation depends on your computer facilities and/or the number of signal to process.

H/V output

Once the computation of the H/V ratio is finished, an on-screen results sheet entitled 'HV results' appears (see Figure 1). there is one sheet per 3-components signal. The presentation of this sheet is always the same: the average H/V ratio (i.e. the H/V ratio computed with the quadratic mean of both horizontal Fourier amplitude spectra) and the standard deviation are shown on the top of the sheet (Figure 1), while the N/V and the E/V ratio are shown in the middle and in the bottom, respectively. 'N/V' ratio means the North-South to vertical Fourier amplitude spectral ratio, and 'E/V' means the East-West to vertical Fourier amplitude spectral ratio. By default the X axis (frequency) is shown in logarithmic scale and the Y axis (th H/V ratio amplitude) in linear scale. You can change it by activating the H/V plot (click inside the plot) and click on menu "Format/X(Y) axis properties". Then click on the "Format" tab and turn on/off the "Log" option. By navigating in the different tabs, you can also change the appearance of the figure (axis limits, axis length, labeling ...).

The Fourier amplitude spectra is shown in the same way in a sheet entitled 'Spectral amplitudes'. The smoothed Fourier amplitude spectra for the vertical, the North-South, and the East-West components are shown, respectively, at the top, middle and bottom of the sheet. You have acess to the same parameters as the H/V sheet to change the appearance of the figure.

H/V ratio output

Figure 1: H/V ratio output

At your own convenience you can choose how to plot the H/V results. In the H/V results sheet, click on menu "Format/Option". The options tool box window is now open (Figure 2). You can turn on/off several options (Table 1) for the three ratios (H/V, N/V and E/V) all together or individually. To turn on/off the option, simply check/uncheck the corresponfing box.

Options for plotting H/V results

Figure 2: Options for plotting H/V results

Table 1: description of the options to plot the H/V ratio
Option Description
T10 Define the reliable frequency range of the H/V computation. Frequencies lower than the minimum reliable frequency are hachured in red. The minimum reliable frequency is estimated from the window length: Fmin= 10/(average window length); see Figure 3
Frequency limits Define the average H/V ratio peak frequency and the standard deviation estimated from the H/V ratio computed from all windows. A gray rectangle centered at the average H/V ratio frequency peak (Fhv) is plotted on the H/V curve. The size of the rectangle is defined by the standard deviation (std): Fmin=Fhv/std and Fmax=Fhv*std; see Figure 3
All windows Plot in color H/V ratio curves computed from each window. The same color scale as H/V curves is used to highlight the corresponding windows in the signal viewer. By this way, one can easily identify which time window produce H/V curve; see Figure 4
Average Plot the average H/V ratio curve
Stddev Plot the standard deviation derived from all H/V ratios
Option descriptions

Figure 3: Reliable frequency range and average H/V ratio frequency peak

Option descriptions

Figure 4: (top) H/V curves computed from all time windows; (bottom) corresponding time windows

H/V summary

If more than two H/V ratios are computed at the same time, then an on-screen H/V summary appears at the end of the computation (Figure 5). All average H/V ratio curves are displayed in the same time. For each station, the H/V amplitude is displayed according to the distance from the reference station (the first station in the list) and frequency. The distance between each station and the reference station is given by sqrt(dx*dx+dy*dy), where dx and dy are the relative distance bewteen stations along the X (East) and Y (North) direction. Then a map with X,Y coordinates of station and the H/V peak frequency plotted with color circle is displayed.

H/V summary

Figure 4: H/V summary: all H/V curves (top), H/V amplitude plotted according to the distance from the reference station and frequency (middle), map with X,Y coordinates of station and the H/V peak frequency plotted with color circle (bottom)


To restrict manually the interval for searching the H/V peak frequency click on menu "Tools/Adjust frequency peak" and set the minimum and the maximum frequency interval. You can also add a new peak frequency band in case of multiple peaks on H/V curves.

To compare two H/V curves using the student-t-test, click on "Tools/Statistical comparison". Select the curve (average H/V, N/E or E/V) and the reference curve. Give the value of the "Test's significance". See the SESAME Final report WP02 on H/V techniques: experimental conditions (D08.02) for more details on the student-t-test.

To switch between H/V and spectra sheets, click on menu "Tools/Spectral amplitudes" or "Tools/HV results".

To derivate or integrate the Fourier spectra amplitudes, click on "Tools/Derivate or Integrate".

Saving the results

To save the H/V and spectra curves as text files (*.hv and *.spec), click on menu "File/Save results as ..." in the H/V or spectra sheet.

To save the sheet as XML text file (*.page), click on menu "File/Save as ..." in the H/V or spectra sheet.

To save the make-up of the sheet as XML text file (*.mkup), click on menu "Format/Save make-up ..." in the H/V or spectra sheet.

To export the sheet as an image file (*bmp, *.jpeg, *png ...), click on menu "File/Export image" in the H/V or spectra sheet.

When H/V is launched with signals displayed in a table, the .hv and .spec files are directly saved in a directory.