Surface soil classification was derived using the method developed by Allen and Wald (2009) which uses topographic data as a proxy for site conditions. The soil maps derived using this methodology show the shear wave velocity of seismic waves in the top 30 meters of soil, which is denoted as Vs30. High values of Vs30 (e.g., greater than 760m/s) refer to hard rock site conditions, which show no significant amplification of incipient seismic waves. Very low values of Vs30 (e.g., lower than 180m/s) refer to very soft soil sites where significant amplification is expected. Average medium to stiff soil conditions have Vs30 values in the 300 to 500m/s range. Although these maps are developed according to the current state-of-the-art approach, it should be noted that in some cases discrepancies may be found between the values of Vs30 estimated by this method and those that may be measured in the field. Data Source: Soils are derived from topographic slope using methodology by Allen and Wald [2009] based on SRTM4 data. The resolution is 9-arc second. The data cover all of the 15 countries. Compiled by AIR Worldwide.
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