H/V spectral ratio

This a short tutorial presenting a step-by-step H/V method procedure.

Introduction

H/V curve example

The technique originally proposed by Nogoshi and Igarashi , and wide-spread by Nakamura, consists in estimating the ratio between the Fourier amplitude spectra of the horizontal (H) to vertical (V) components of ambient noise vibrations recorded at one single station.

This tool is used to obtain Horizontal to Vertical (H/V) spectral ratios from any type of vibration signals (ambient vibrations, earthquake…). The example used for explanations is an ambient vibration recording.

All parameters necessary to process signal data are set up in the Toolbox.

The reference document for the H/V processing is the SESAME user guidelines, which is strongly recommended for further reading .

As for the other tools, the data can be processed:

• from a graphic viewer, to verify the windowing and to display the results;
• from a table. In this case, Geopsy will display only the resulting curves.

Getting ready

• Download the compressed signal file.
• Load and view these downloaded signals.
• Select H/V spectral ratio in menu Tools (drag&drop alternative way to start a tool)

Window selection

General sub-tab in Time tab of the H/V toolbox

• Make sure that the H/V Toolbox is displaying the Time tab, and that parameters are set as in the example window. The Anti-triggering on raw signal button has to be checked.
• To ensure that parameters are alright, it is possible to download the tutorial parameter file and to load the toolbox parameters.

Raw signal sub-tab in Time tab of the toolbox with the anti-trigger parameters

• Click on the Raw signal sub-tab in Time tab, to check that the anti-trigger parameters, used to get rid of saturated signal, are as in the example window.

Select pop-up menu

• Click on the Select button and select Auto.

Number of selected windows

• The number of selected windows appears at the bottom right corner of the Time tab.
  The number of windows should be as in the example.

Selected windows

• Selected windows should appear as green rectangles on the Signal viewer.

• More options for selecting windows are available.

Processing parameters

Processing tab in toolbox

• Click on the Processing tab, and make sure that parameters are as in the example window.

Output parameters

Output tab in toolbox

• Make sure that you are in the Output tab, and that parameters are as in the example window.

Data processing

• Click on the Start button at the bottom of the toolbox, whatever tab is displayed.

No selected windows pop-up window

• If no window selection has been performed, a pup-up window appears.

Simply click on the Yes button and processing will follow its way.

Results

Signal display

Signal display with colored windows used for computing H/V matching with colours of individual H/V curves presented below

• Selected windows are colored, matching colours in he H/V graphics, i.e. colour of individual H/V curves have the same colour as the signal windows.

H/V curve

H/V curve

• The blak curve represents H/V geometrically averaged over all colored individual H/V curves The two dashed lines represent H/V standard deviation.
• The grey area represent the averaged peak frequency and its standard deviation. The frequency value is at the limit between the dark grey and light grey areas.

Peak frequency and standard deviation values

• Use the cursor to get values on the H/V curve. The exact value of the H/V peak frequency and its standard deviation may be obtained by sliding the cursor onto the H/V curve title (Strong_peak) in the upper right corner above the graphics.

Changing H/V graphics appearance

Pop-up menu to restore a make-up

• It is possible to change the appearance of the H/V graphics at the user's will, using a make-up.
• As an example, first download the compressed make up file.
• Then right click in the left hand margin of the H/V graphics.
• Select Restore make-up in the pop-up menu and then select HV_Makeup.mkup file.

New H/V graphics appearance change after applying a make-up

• The appearance of the H/V graphics is now at the user's taste.

Saving results

Pop-up menu to save H/V graphics

• The H/V graphics may be saved in various image formats.
• Right click in the left hand margin of the H/V graphics.
• In the pop-up menu choose Export image.

Directory were to save H/V graphics

• Choose a destination folder, image format, and file name.