منبع : سیویل استارز
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Site effects associated with local geological conditions constitute an important part of any seismic hazard assessment. Many examples of catastrophic consequences of earthquakes have demonstrated the importance of reliable analyses procedures and techniques in earthquake hazard assessment and in earthquake risk mitigation strategies. Ambient vibration recordings combined with the H/V spectral ratio technique have been proposed to help in characterising local site effects. This document presents practical user guidelines and software for the implementation of the H/V spectral ratio technique on ambient vibrations.
The H/V spectral ratio method is an experimental technique to evaluate some characteristics of soft-sedimentary (soil) deposits. Due to its low-cost both for the survey and analysis, the H/V technique has been frequently adopted in seismic microzonation investigations. However, it should be pointed out that the H/V technique alone is not sufficient to characterise the complexity of site effects and in particular the absolute values of seismic amplification. The method has proven to be useful to estimate the fundamental period of soil deposits. However, measurements and the analysis should be performed with caution. The main recommended application of the H/V technique in microzonation studies is to map the fundamental period of the site and help constrain the geological and geotechnical models used for numerical computations. In addition, this technique is also useful in calibrating site response studies at specific locations.
These practical guidelines recommend procedures for field experiment design, data processing and interpretation of the results for the implementation of the H/V spectral ratio technique using ambient vibrations. The recommendations given here are the result of a consensus reached by the participants of the European research project SESAME (Contract. No. EVG1-CT-2000-00026), and are based on comprehensive and detailed research work conducted during three years.
It is highly recommended that prior to planning a measurement campaign on ambient vibrations, a local geological survey, especially on Quaternary deposits, should be performed. Interpretation of the H/V results will be greatly enhanced when combined with geological, geophysical and geotechnical information.
In spite of its limitations, the H/V technique is a very useful tool for microzonation and site response studies. This technique is most effective in estimating the natural frequency of soft soil sites when there is a large impedance contrast with the underlying bedrock. The method is especially recommended in areas of low and moderate seismicity, due to the lack of significant earthquake recordings, as compared to high seismicity areas
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