Analysis of earthquake-prone areas based on the seismic wave velocity, young's modulus, shear modulus, and Poisson’s ratio for disaster risk reduction in Bengkulu city, Indonesia

Bengkulu City is the capital of Bengkulu Province, Indonesia. This city is situated adjacent to a Subduction zone and is intersected by several faults. The goals of this study are to determine the depth of the highly compacted soil layers as well as the wave velocity at a depth of 30 m (Vs30) to identify and map the area based on its mechanical characteristics indicated by various parameters such as the seismic wave velocity, Young’s modulus, shear modulus, and Poisson’s ratio. Data acquisition was carried out using a digital seismograph instrument. Field information for the seismic shots was collected for analysis using the Win-MASW 5.0 Professional Software. These mechanical parameters serve as the foundation for data processing and interpretation of the structure of the underlying rock and soil layers. The study findings indicate that the sub districts of Muara Bangkahulu, Ratu Agung, Sungai Serut, and Teluk Segara are all areas with a heightened potential for earthquake hazards. The soil in Bengkulu City is categorized into three groups based on the Vs30 values: soft soil, stiff soil, and a very dense soil layer found at depths ranging from 2.8 to 31.5 m below the surface. The presence of subduction zones influences the formation of tectonic plate buckling which causes the landforms in this area to undulate. The presence of faults at the study location can also reduce the density of the surrounding rocks. In basin areas that are buried by sediment and low rock density, this influences the low Vs30 value. The Vs30 value is also correlated with other rock mechanical parameters. In rocks with low density, apart from having a low Vs30 value and also having a seismic wave velocity value, Young’s modulus and shear modulus are low, but Poisson’s ratio value is high. This condition can influence the threat of greater earthquakes and high seismic vulnerability. Efforts needed to reduce disaster risk are to avoid areas that have high seismic vulnerability which are characterized by low seismic wave velocity, Young’s modulus and shear modulus values, but high Poisson’s ratio values.