SEISMIC SITE CLASSIFICATION OF NAN CITY, NORTHERN THAILAND

Abstract

The primary goal of this study is to generate the NEHRP soil classification map for Nan City using the average shear wave velocity values (Vs₍₃₀₎) derived from the multichannel analysis of surface wave (MASW) data. The secondary goal is to use the Vs₍₃₀₎ data to create the preliminary site amplification map of the area. For this work, MASW data were acquired at 36 preselected sites in the Nan City area. After generating the NEHRP map, it is found that soil class D is present mostly in the central and southeast part of the area, while soil class C is found mainly in the western, eastern, and southern parts. A major part of the city is located on soil class D. The soil amplification map indicates higher amplification in the central and southeast part of the city, where the soil consisted mainly of soft sediments from the alluvial plain and the river terrace. The western, eastern, and southern parts of Nan City had a relatively low amplification, perhaps because the sediment in this part is relatively thin or the bedrock is shallow. The results of the study imply that the major part of Nan city may experience earthquake ground shaking due to amplification of the soft soils.