This study investigates the correlation between shear wave velocity (VS) and standard penetration test blow counts (SPT-N value) in all soil types, gravelly soil, sandy soil and clayey soil for Mashhad city in the north eastern region of Iran. The VS data used were measured through downhole method in 84 construction projects (in 88 boreholes). From among collected data, 424 pairs of VS-SPT recorded in one depth were used for regression analysis. The obtained results showed that the N-value had a critical role in estimating VS and soil type was less effective in this regard. These findings are in line with the findings of the previous studies. Regression equations obtained in this study were compared with correlations from previous studies. There was a relative similarity between the previously published and the new regression equations for Iranian soils. Although almost all correlations follow a similar trend, there are significant differences between new equations and correlations reported for other countries. The regression coefficients of the new equations show the acceptable capability of the suggested correlations in estimating VS through SPT-N value. Therefore, these equations can be used to estimate VS for the soils of the current study area and for other similar areas. Moreover, VS30 was used for site classification of the study area as per National Earthquake Hazard Reduction Program (NEHRP) guidelines and it was shown that a major portion of the city comes under site class C and other locations are categorized as site class D.
