Empirical correlations of shear wave velocity (Vs) and penetration resistance (SPT-N) for different soils in an earthquake-prone area (Erbaa-Turkey)

The seismicity of the northern part of Turkey is mainly controlled by the North Anatolian Fault zone (NAFZ). The NAFZ is one of the worldʹs most active seismic zones, and has produced destructive earthquakes and related hazards in the northern region of Turkey. Several earthquakes and earthquake-related hazards have occurred along different segments of this fault zone in the recent past. The study area, Erbaa town, is located along the eastern segment of North Anatolian Fault Zone (NAFZ) and is one of the largest towns of Tokat Province in the Middle Black Sea Region of Turkey. The center of Erbaa is located on the left embankment of the Kelkit River. After the disastrous 1942 (Ms = 7.2) and 1943 (Ms = 7.6) earthquakes, the settlement was shifted southwards. art of a seismic microzonation study of the Erbaa area, shear wave velocity (Vs) values of the geological units exposed in this area were required for site response analyses. The geological units in the study area consist mainly of alluvial and Pliocene units. These layers were evaluated on the basis of drilling, in-situ (SPT, SCPTU and SPT-based uphole) and laboratory testing. In this study, empirical correlations between shear wave velocity (Vs) and standard penetration test blow counts (SPT-N) were considered in order to define shear wave velocity profiles for the study area. The relationships between shear wave velocity, Standard Penetration Test (SPT) blow-counts and the soil properties were evaluated as functions of depth. SPT-based uphole tests were performed to measure shear wave velocity during drilling operations in some of the borings. The SPT-based Vs values were computed with different empirical formulas and compared with the measured SPT–based uphole Vs measurements. The empirical correlations were found to require modification to provide the best correlation for this site. The depth factor was considered during the development of new empirical equations. Therefore, a site-specific formula was proposed in order to obtain Vs profiles for all layers in the study area.