Seismic microzonation in Bengkulu City, Indonesia: insights for resilient planning after 2000 Mw 7.9 and 2007 Mw 8.4 earthquakes

Abstract

Bengkulu city, located in the western part of Sumatra, is characterized by the prevalence of alluvial deposits. In certain areas, local site effects on soft alluvial sediments such as clay, sand, silt, mud, and gravel can amplify ground movements caused by significant seismic waves. Consequently, a comprehensive site effect study was conducted with closer measurement points to establish a more detailed seismic microzonation. In order to evaluate how the soil reacts to seismic activity, the HVSR method is performed to analyze the ambient soil noise within the study area. Field measurements reveal variations in the predominant frequency (ranging from 0.4 to 16.5 Hz), HVSR amplification (ranging from 0.3 to 12.3), and K_g distribution (ranging from 0.02 to 239.26), respectively. Furthermore, the PGA Kanai method was utilized to estimate soil shear strain (GSS) in the study area, using data from the 2000 Bengkulu-Enggano Earthquake (Mw 7.9) and the 2007 Bengkulu-Mentawai Earthquake (Mw 8.4). The analysis indicated a consistent distribution of K_g values with GSS and PGA values, alongside Modified Mercalli Intensity (MMI) values, exhibiting correlation coefficients greater than 0.9. This suggests that Bengkulu City faces a moderate to high vulnerability to severe damage from earthquakes. The closer examination of HVSR data at finer measurement points aids in identifying exposure to new hazards and contributes valuable insights for formulating regional planning policies centered on disaster risk reduction and enhancing existing strategies in Bengkulu City.