Seismic Site Characterization and Vs30 Mapping in Semarang City, Indonesia using Multichannel Analysis of Surface Waves

Semarang, Indonesia, is a densely populated city with high seismicity due to active fault zones such as the Semarang and Ungaran faults. Local site characterization is essential for seismic hazard assessment and as a reference for urban development. This study applied the Multichannel Analysis of Surface Waves (MASW) method at 140 locations across Semarang to estimate shear wave velocity (Vs) structure and calculate the average shear wave velocity in the upper 30 m (Vs30). Data acquisition was conducted by using a 24‐channel linear array with 2‐m geophone spacing and a 10 kg sledgehammer source. The results reveal distinct spatial variations in site conditions. Based on NEHRP Site Classification, the southern part of Semarang is primarily classified as Site Class D (medium soils), while the northern part is dominated by softer soils, classified as Site Class E (Soft soil). These results correlate well with borehole data and local geology, confirming the reliability of MASW for seismic site characterization. The areas that consist of soft soils will be more vulnerable to seismic wave amplification, which causes greater seismic risk. This study provides crucial input for the development of seismic microzonation, building code refinement, and seismic risk reduction programs in Semarang city. The methodology and findings can also serve as a reference for other urban areas with similar geological and seismic settings.