• The Journal of Engineering Geology
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• v.24 no.2
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• pp.273-281
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• 2014

In most current seismic design codes, design earthquake ground motions are defined by a reference spectrum, based on bedrock and site amplification factors that quantify the geotechnical dynamic conditions. Earthquake engineering bedrock is the fundamental geotechnical formation where the seismic waves are attenuated without amplification. To better define bedrock in an earthquake engineering context, shear wave velocity ($V_S$ ) data obtained from in-situ seismic tests were examined for several rock strata in Korea; these data were categorized by borehole drilling investigations. The $V_S$ values for most soft rock data in Korea are > 750 m/s, which is the threshold $V_S$ value for identifying engineering bedrock from a strong motion station. Conversely, VS values are < 750 m/s for 60% of $V_S$ data in weathered rock in Korea. Thus, the soft (or harder) rock strata below the weathered rock layer in Korea can be regarded as earthquake engineering bedrock.