Geopsy: H/V and Spectrum Toolboxes: Processing Tab

Processing tab giving access to smoothing, parameters (for windows) and how is processed the H/V (available only for H/V computing)

Here are described the different possibilities offered in this tab. This tab is divided in two areas:

-Parameters area

-Horizontal components

Parameters area

Processing tab giving access to smoothing, parameters (for windows) and how is processed the H/V (available only for H/V computing)

This area, common for H/V and Spectrum computings, is divided in three different parts with three different objectives :

Smoothing

Fixing which smoothing will be applied to the windows (2 first lines). During the computing of H/V or Spectrum, the Fourier spectra can be smoothed (it is strongly recommanded) in the goal to clarify the global aspect of the curves.

For Spectrum, each Fourier spectrum (coming from a window) is smoothed and then the averaged curve is computed.

For H/V, the horizontal Fourier spectra (NS and EW, coming from a synchronous window) are first added and then the smoothing is applied on the merged horizontal Fourier spectrum and on the vertical Fourier spectrum.

There are 4 possibilities for the smoothing:

1. no smoothing. This can be sometime usefull to have a rough idea about Fourier spectra;
2. Konno and Ohmachi smoothing. This smoothing use a constant bandwidth in a logarithmic scale and is strongly recommanded because this smoothing function preserves the different number of points at low and high frequency. This smoothing is controled by a smoothing constant varying in-between 0 and 100. A constant of 0 gives a very strong smoothing, when a constant of 100 a very soft smoothing, more details;
3. Constant smoothing. This smoothing function has a triangular shape centered on the current frequency and its width is equal to "Band width" given by the user. This band width varies from 0 (soft smoothing) to 100 (strong smoothing);
4. Proportional smoothing. This smoothing function has a triangular shape and its width depends upon the current frequency. The half width is defined by percentage*frequency. The value of "percentage" cannot be greater or equal to 100% (strong smoothing).

Whatever the smoothing method used, even if the impact of the smoothing is minimized, the result will be different from a processing without smoothing.

Taper

Fixing the use or not of a cosine taper on the individual window.

In the goal to minimize the border effect due to the extraction of a window and so improve its properties in the frequency domain, it is strongly recommended to use a taper to avoid the creation of parasit frequencies.

Filter

Fixing the use or not of a filter on the whole signal.

This option allows to filter the signal before the extraction of the time windows.

To the contrary of the Waveform menu filter there is only a "High pass" filter allowed, rejecting frequencies below a given value

Be carefull with this option. As the signal is high pass filtered, the results below the choosen frequency will display a lake of data.
If the studied frequency is close to 1 Hz and it is applied this filter at 2 Hz, the results will lead to bad data in the frequency of interest
and then to flaky interpretation.

Horizontal components area

This area is devoted to indicate how the H/V has to be computed. There are 3 different methods that can be applied.

Processing tab giving access to smoothing, parameters (for windows) and how is processed the H/V (available only for H/V computing)

Squared average

Fourier amplitude spectra (for each window) combination of horizontal spectra (for each window) smooth of H and V (for each window) computation of H/V

Total horizontal energy

Fourier amplitude spectra (for each window) combination of horizontal spectra (for each window) smooth of H and V (for each window) computation of H/V

Directional energy

Konno K. and T. Ohmachi, 1998. Ground motion characteristics estimated from spectral ratio between horizontal and vertical components of microtremors. Bull. seism. Soc. Am., 88-1, 228-241