Parametrical Model for Estimating VS30 from Shallow Borehole Profiles Using a Database for China

ABSTRACT Employing extrapolation models to estimate the time-averaged shear-wave velocity to 30 m (VS30) from a shallow borehole profile is an effective way to expand the VS30 data volume and a necessary initial step for developing VS30 proxy models. Past extrapolation model studies have relied only on shallow borehole shear-wave velocity (VS) profiles to estimate VS30. In this study, we enhance the model by accounting for additional parameters including location slope, geologic age, and geotechnical class. We first compile a new borehole profile database (BPDB) that contains information about 8831 boreholes in China. Using this BPDB, we analyze the VS characteristics of strata for various location slopes, geologic ages, and geotechnical classes. The result shows that the location slope and geologic age have significantly different effects on the VS characteristics, whereas the differences for sand, silt, and clay are small. We build a parameter classification scheme that classifies the location slope into six groups, the geologic age into seven hierarchical types, and the geotechnical class into four hierarchical types. This scheme ensures that each group/type has its distinctive VS characteristic. We evaluate five existing VS models and choose the model that shows the best performance on the BPDB as the “prototype” model. We classify the BPDB boreholes by the parameter classification scheme and use the form of “prototype” model to develop a parametrical model that consists of 33 single-parameter-value models. For a shallow borehole (<30 m), if its location slope, geologic age, or geotechnical class is available besides its VS profile, applying the parametrical model will get more accurate estimated VS30 and model uncertainty estimation than those of existing models that only utilize the information of the VS profile.