Geology and topography based Vs30 map for Sylhet City of Bangladesh

Time-averaged shear wave velocity of the soil layers to a depth of 30 m (Vs30) is primarily estimated by different geophysical and geotechnical site investigation techniques, such as downhole and crosshole seismics (DS and CS), spectral analysis of surface waves (SASW), multichannel analysis of surface waves (MASW), and the standard penetration test (SPT). Sufficiently dense field measurements of the Vs30 using these techniques are not feasible for VS30 mapping at a regional scale. Therefore, secondary information, such as geological and topographical constrains are used as proxies to predict the Vs30 for mapping purposes. In the present study, a Vs30 map for Sylhet City has been prepared based on the geological and topographical constrains. The map has five Vs30 units having a distinct mean Vs30 value for each unit. This Vs30 map can be used as an effective proxy to estimate site response of the soil layers in Sylhet City.