Identification of bedrock depth along a downstream segment of Muara Bangkahulu River, Bengkulu City, Indonesia

The downstream area of Muara Bangkahulu River is now becoming one of the developing areas in Bengkulu City. In connection with the limited geological information in the study area, this paper identifies bedrock depth along the river’s downstream segment. This study is initiated by collecting site investigation data, including soil profile and ambient noise measurement. The inversion analysis using the Monte Carlo simulated annealing method generates a one-dimensional shear wave velocity profile. The results indicate that areas located near the coastline which are developed as tourism areas are categorised as having high-seismic vulnerability. In contrast, the trading market which is close to the river is categorised as having very high seismic vulnerability. In addition, the study area is categorised as Site Classes C and D. A larger vulnerability level is generally found in areas having low V_s30 and Site Class D. The results indicate that soft rock or engineering bedrock is identified at a depth of 5 to 91 m depth, medium rock at a depth of 10 to 222 m, and hard at a depth of 40 to 289 m. Information on bedrock depth could be implemented to simulate seismic wave propagation for further study.