IDENTIFYING THE LOW VELOCITY LAYER IN GELORA BANDUNG LAUTAN API STADIUM, GEDEBAGE, BANDUNG USING MULTICHANNEL ANALYSIS OF SURFACE WAVES (MASW) METHOD

Abstract

Gedebage, located in the Bandung area, is historically part of an ancient lake basin surrounded by multiple fault zones. As the lowest point of the former lake, this region has accumulated ancient lake sediments composed primarily of low velocity lithologies such as clay, sandstone, and gravel. The purpose of this study is to characterize the subsurface conditions in the Gedebage area, particularly to assess soil classification and its implications for seismic vulnerability. The Multichannel Analysis of Surface Waves (MASW) method was employed due to its effectiveness in identifying shallow subsurface materials and its applicability in assessing soil stiffness for earthquake disaster mitigation. Five survey lines were deployed in and around the main stadium area. The results show that the Gedebage subsurface generally consists of soft to medium soils, with the softest materials located within the top 5 meters. Notably, the second and fourth lines positioned outside the main football field recorded the lowest velocities, with a minimum of 110 m/s, indicating soft soil. In contrast, the first line situated within the stadium showed a significantly higher least velocity of 174 m/s. Low velocity layer has a direct relationship with the amplification from the subsurface, site classification based on Vs30 is used to define the expected ground motion amplification due to local soil conditions. A lower Vs30 corresponds to softer soils or a low velocity layer. The Vs30 values further support these findings, with the first line measuring 238 m/s, while the second and fourth lines registered 185 m/s and 178 m/s, respectively. Overall, this study provides valuable insight into the geotechnical characteristics of Gedebage and supports the use of MASW as a practical method for seismic site classification and mitigation planning in urban development on soft sedimentary basins.