A new Vs30 prediction strategy taking geology, terrain, and saturation into account: application to Türkiye

Okay, Hakan Bora
Various parameters are used for geotechnical characterization of site conditions. Among them, most widely used one is average shear wave velocity in upper 30 meters (Vs30). So far, many different proxy-based approaches are proposed to predict Vs30 across large-scale areas where geophysical measurements are limited or absent. In this study, elevation and slope of Vs30 measurement locations in Türkiye and California are determined using high-resolution digital elevation model along with their geologic unit and terrain classes. Their correlation with measurements indicate that Vs30 is sensitive to various site properties and thus should be treated as multi-factor dependent parameter. In order to improve accuracy, new Vs30 prediction strategy is developed. In this approach, geologic units are classified into 4 sedimentary rock classes according to their ages (Quaternary-Pliocene, Miocene, Paleogene, Pre-Paleogene) and 3 non-sedimentary rock classes (Intrusive, Extrusive, Metamorphic).Vs30 measurements from Quaternary-Pliocene rocks are most abundant and characterized by large data scatter thus further divided into 2 terrain classes (Mountain/Hill, Plain/Terrace). Since reduction in Vs30 due to fluid saturation is pronounced especially in unconsolidated young units, Quaternary-Pliocene rocks are also differentiated as saturated if water table less than 30 m and unsaturated otherwise. In the absence of borehole measurements, flat areas with height difference less than 30 m from surface water bodies (sea, lake, and major rivers) are mapped out in Türkiye as saturated using water level rise analysis. After elimination of outliers, slope and elevation based Vs30 prediction equations are developed separately for sub-classes of Quaternary-Pliocene, Miocene, and Paleogene aged sedimentary rocks using linear regression with multivariable while Vs30 is fixed to class average in others. Our prediction strategy performed better in young units than others and provided a new, more accurate Vs30 map of Türkiye.


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Citation Formats
H. B. Okay, “A new Vs30 prediction strategy taking geology, terrain, and saturation into account: application to Türkiye,” M.S. - Master of Science, Middle East Technical University, 2022.