What is V_S30?

V_S30 is average shear-wave velocity of the top 30 m of the earth. It is an important parameter used in classifying sites in building codes. It is widely applied in earthquake engineering, including ground-motion prediction equations, earthquake loss estimation, earthquake insurance, etc.

V_S30 is computed by dividing 30 m by the travel time from the surface to 30 m.

where d_i = the thickness of any layer between 0 and 30 m, V_si = the shear wave velocity in m/s, and the sum of d_i is 30m.

Why do we need a extrapolated V_S30?

Although V_S30 is a simplified index for the characterization of soil properties, it is impractical to conduct the requisite densely spaced direct measurements for large areas. For a number of reasons, V_S profiles are often not available to a depth of 30 m. Therefore, in terms of the applications to hazard mapping, earthquake fatality/loss impact estimation, earthquake insurance models, and so forth, which are designed to use at regional or even national scales, it is sometimes necessary to estimate V_S30 from shallow borehole profiles at the same site to expand the data volume.

How accurate does a extrapolated V_S30 hold?

V_S30 extrapolation can help expand the data volume while inevitably introducing uncertainty into the extrapolated result. Here, the uncertainty is presented by the model RMSE, which is defined by:

in which i means the ith sample data used in developing the extrapolation model, and n is the total number of samples.

What model is the extrapolation method of this website based on?

The extrapolation method of this website is based on the scientific article: Zhou Jian., Xiaojun. Li, Zhijun. Dai, and Kun. Chen (2021). Parametrical Model for Estimating V_S30 from Shallow Borehole Profiles Using a Database, Bull. Seismol. Soc. Am. 111(3) 1199-1220.

Link：https://doi.org/10.1785/0120200178

https://www.researchgate.net/profile/Jian-Zhou-125

Abstract：Employing extrapolation models to estimate the time-averaged shear-wave velocity to 30 m (V_S30) from a shallow borehole profile is an effective way to expand the V_S30 data volume and a necessary initial step for developing V_S30 proxy models. Past extrapolation model studies have relied only on shallow borehole shear-wave velocity (V_S) profiles to estimate V_S30. 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 V_S 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 V_S characteristic. We evaluate five existing V_S 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 V_S profile, applying the parametrical model will get more accurate estimated V_S30 and model uncertainty estimation than those of existing models that only utilize the information of the V_S profile.

How can the information of location slope, geotechnical profile, and geologic profile of a borehole benefits the V_S30 extrapolation?

Besides the V_S profile, the method introduced in the article ‘Parametrical Model for Estimating V_S30 from Shallow Borehole Profiles Using a Database for China’ using location slope, geologic age, and geotechnical class as supplemental parameters to enhance the performance of the extrapolation model. In the article, 33 single parameter-value models correspond to 33 different supplemental parameter values.

For a shallow borehole (<30 m), if its location slope, geologic age profile, or geotechnical class profile are available besides its V_S profile, applying these parameters in the model will get more accurate estimated V_S30 and model uncertainty estimation than only using the information of the V_S profile.

Can this tool extrapolate V_S20 or V_S of other depth values?

Unfortunately, currently the tool on this website does not has the function of extrapolating V_S20 or average shear-wave velocity of other depth values. But we are working on developing a more general model to do that.

Can this tool extrapolate the V_S profile of a borehole?

Unfortunately, currently the tool on this website does not has the function of extrapolating the V_S profile of deeper layers of a borehole. But we are working on developing a more general model to do that.