Mapping Vs30 in Taiwan

The average shear-wave velocity of the upper 30 meters of a soil profile (Vs30) is a key indicator of site response dominating the ground-motion amplification. The primary purpose of this study is to map the distribution of Vs30 in Taiwan using available data and multivariate geostatistical techniques. Data from 230 boring and PS logging at soil and soft rock strong-motion station sites were used to establish the spatial relationship between the shear-wave velocity (Vs) and the N value of standard penetration test (SPT-N). The resultant model was then used to estimate the shear-wave velocity at each depth of a borehole from the Geo2005 database of the Central Geological Survey (CGS) of Taiwan. Finally, a geostatistical method called "kriging with varying local means" was applied to generate a Vs30 distribution map of Taiwan. The site classification results can be updated for Taiwan's strong-motion stations based on this new Vs30 map and actual site measurements.