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H/V curve example

General sub­tab in Time tab of the H/V toolbox

H/V spectral ratioFrom GeopsyWiki

This a short tutorial presenting a step­by­step H/V method procedure, using some of the main parameters.

For a more detailed description of the Toolboxes parameters see H/V and Spectrum Toolboxes

Contents1 Introduction2 Getting ready3 Window selection4 Processing parameters5 Output parameters6 Data processing7 Results

7.1 Signal display7.2 H/V curve

8 Changing H/V graphics appearance9 Saving results

9.1 Image formats9.2 Numerical values

10 References

Introduction

The technique originally proposed by Nogoshi and Igarashi [1], and wide­spread by Nakamura[2],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 vibrationrecording.

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

For H/V processing, the data should have:

3 signals: North­South, East­West and Vertical;a common name (see here to modify the name of the component);enought common samples in time to be processed.

So, the user has to be careful when the 3 signals of a same recording are loaded from 3 different files.In some early versions (before 2010­06­01), failing to fulfill those conditions may lead to results basedon silently stacked signals, for instance, when signal Name is no set in file header (e.g. column textfiles without header).

As for the other tools, the data may 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.

The reference document for the H/V processing is the SESAME user guidelines, which is stronglyrecommended for further reading [3].

Getting readyDownload 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 selectionMake sure that the H/V Toolbox is displaying the Time tab, and that parameters are set as in the example window.The Anti­triggering 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 toolboxparameters.

Click on the Raw signal sub­tab in Time tab, to check that the anti­trigger parameters, used to get rid of saturated signal, are as in the example window.

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Raw signal sub­tab in Time tab of the toolbox withthe anti­trigger parameters

Select pop­upmenu

Number of selected windows

Selected windows

Click on the Select button and select Auto.

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 should appear as green rectangles on the Signal viewer.Notice that the selected windows are common for the three components.

More options for selecting windows are available.

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

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Processing tab in toolbox

Output tab in toolbox

No selected windows pop­up window

Signal display with colored windows used forcomputing H/V matching with colours of individualH/V curves presented below

Output parametersMake 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.

If no window selection has been performed, a pop­up window appears.

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

ResultsSignal display

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

H/V curve

The black curve represents H/V geometrically averaged over all colored individual H/V curves. The two dashed lines represent the 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.

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H/V curve

Peak frequency and standard deviation values

Pop­up menu to restore a make­up

New H/V graphics appearance change afterapplying a make­up

Pop­up menu to save H/V graphics

Directory were to save H/V graphics

Use the cursor to get information on the H/V peak. By sliding the cursor onto the H/V graph or title, the followinginformation appear in a yellow frame: data file name, exact value of the H/V peak frequency and its standarddeviation, exact value of the H/V peak amplitude and its standard deviation, and interpretation category.

Changing H/V graphics appearanceIt is possible to change the appearance of the H/V graphics at the user's will, using a make­up.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 make­up in the pop­up menu and then select HV_Makeup.mkup file.

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

Saving resultsThe H/V graphics may be saved in various image formats.

Image formats

Right click in the left hand margin of the H/V graphics.In the pop­up menu choose Export image.

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

Numerical values

Numerical values can be saved in .hv text files.

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Select all stations to saveGo to menu Tools/Save results

It works the same way as the Output section of the toolbox.

References1. ↑ Nogoshi M. and Igarashi T. (1971) On the amplitude characteristics of microtremor (part 2) (in Japanese with english abstract). Journal of seismological Society of

Japan, 24, 26­40.2. ↑ Nakamura, Y. (1989) A method for dynamic characteristics estimation of subsurface using microtremor on the ground surface. Quaterly Report of the Railway

Technical Research Institue 30 (1), 25­30.3. ↑ Guidelines for the implementation of the H/V spectral ratio technique on ambient vibrations measurements, processing and interpretation, [1] (http://SESAME­

FP5.obs.ujf­grenoble.fr) , 62 pages, April 2005

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This page was last modified on 8 January 2013, at 16:49.Content is available under GNU Free Documentation License 1.2.